Title of Invention	METHOD OF MAKING MERCAPTOALKYLALKOXYSILANES
Abstract	In a first embodiment of a process for making mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, are mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts.

Title of Invention

METHOD OF MAKING MERCAPTOALKYLALKOXYSILANES

Abstract

In a first embodiment of a process for making mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, are mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts.

Full Text	METHOD OF MAKING MERCAPTOALKYLALKOXYSILANES [0001] This invention relates to the synthesis of mercapto-functional organosilicon compounds =Si-(CH2)nSH, more particularly mercaptoalkylalkoxysilanes such as mercaptopropyltrialkoxy silane (MPTAS), using phase transfer catalysts. The process is capable of producing high purity mercaptopropyltriethoxysilane (MPTES), for example. Mercaptoalkylalkoxysilanes made by the process generally have a formula corresponding to Z-Alk-SH in which Z is one of a group consisting of—SiR12R2, —SiR1R22, and—SiR23; in which R1 is an alkyl group with 1-12 carbon atoms, a cyclohexyl group, or a phenyl group; R2 is an alkoxy group containing 1-12 carbon atoms; and Alk represents a divalent hydrocarbon radical having 1-18 carbon atoms and containing no unsaturation. [0002] Sulfur containing organosilicon compounds are known to be useful as reactive coupling agents between rubber and silica fillers, for improving the properties of cured rubber. They are also known to be useful as adhesion promoters, for adhering rubber compositions to substrates such as glass and metal. However, many sulfur containing organosilicon compounds are difficult to make in good yield, because undesirable byproducts are produced from various side reactions occurring when traditional methods are employed. [0003] For example, US Patent 3,590,065 (June 29, 1971) relates to a reaction between a haloalkylalkoxysilane and a thio-urea in the presence of ammonia. However, the necessity of handling bulky by-products such as guanidine hydrochloride is the major disadvantage associated with this particular method. [0004] US Patent 3,849,471 (November 19, 1974) is directed to another method involving reactions between haloalkylalkoxysilanes and hydrogen sulfide gas in the presence of amines. However, this reaction is carried out under a high pressure, and also has the disadvantage of producing a fluffy by-product salt which is difficult to filter from the end product. [0005] US Patent 3,890,213 (June 17, 1975) relates to yet another method involving reactions between hydrogen sulfide and alkenylalkoxysilanes. However, the major disadvantage associated with this method is that the mercaptosilane product itself can become associated with the alkenylalkoxysilane to form copious amounts of sulfide side products. [0006] In British Patent 1,102,251 (February 7, 1968), a method is described involving the reaction of sodium methoxide and hydrogen sulfide to produce sodium hydrosulfide, which is then further reacted with an haloalkylalkoxysilane. The disadvantage associated with this particular method however, is that the reaction of sodium methoxide with H2S produces sodium sulfide as a by-product, which in turn leads to large amounts of polysulfide silanes in the end product. [0007] US Patent 5,583,245 ((December 10, 1996) describes a process for making compounds generally corresponding to the formula Z-Alk-Sn-Alk-Z, in which Z and Alk are the same as defined above, and in which n is 2-8. According to the process in the '245 patent, a compound of the formula Z-Alk-X where X is chlorine or bromine, is reacted with an ammonium hydrosulfide or an alkali metal hydrosulfide, and sulfur, using a phase transfer catalyst, in an aqueous phase. [0008] The '245 patent teaches that an additional reactant corresponding to Alk-X may be present, where an unsymmetrical compound corresponding to Alk-Sn-Alk-Z is desired, in addition to bis type end products. While the '245 patent does describe a method for preparing MPTES in a 64.9 % yield by reacting (i) sodium hydrosulfide flakes and (ii) chloropropyltriethoxysilane (CPTES), in a saturated sodium chloride solution and toluene solvent, in the presence of a phase transfer catalyst, the yield of MPTES was not optimal. [0009] While US Patent 5,840,952 ((November 24, 1998) describes a method of making mercaptopropylalkoxysilanes in good yield, by purging hydrogen sulfide gas in a sodium sulfide solution in methanol, and then reacting it with chloropropyltrimethoxysilane (CPTMS) in an anhydrous system, the disadvantage associated with this process is that sodium sulfide used must first be dehydrated. Another disadvantage of the '952 patent is that it requires the use of high pressure, i.e., 600 psi/4,140 kilopascal (kPa) hydrogen sulfide gas, to reduce sodium sulfide to sodium hydrosulfide. [0010] In a prior copending application assigned to the same assignee as the present invention, i.e., US Patent Application Serial No. 09/895,719, filed June 29, 2001, and entitled "Preparation of Sulfur Containing Organosilicon Compounds Using a Buffered Phase Transfer Catalysis Process", there is described a process based on phase transfer catalysis. However, this process is directed to the production of bis-type sulfido silanes ?Si-S-Si?, which generally correspond to the formula (RO)3_mRmSi-Alk-Sn-Alk-SiRm(OR)3-m, wherein R is a monovalent hydrocarbon group with 1-12 carbon atoms; Alk represents a divalent hydrocarbon group with 1-18 carbon atoms; m is 0-2; and n is 1-8. According to the process described in the copending application, (A) a sulfide compound M2Sn or MHS wherein H is hydrogen, M is ammonium or an alkali metal, and n is as defined above, is reacted with (B) a silane compound corresponding to (RO)3-mRmSi-Alk-X, wherein X is Cl, Br or I, m is the same as defined above, and (C) sulfur, in the presence of a phase transfer catalyst, in an aqueous phase containing a buffering agent. However, no method is described in the copending application for making mercapto-functional organosilicon compounds, i.e., compounds containing the group =Si-(CH2)nSH. [0011] The copending application, however, results in sulfidosilanes instead of mercaptosilanes. This is because of the presence of elemental sulfur in the copending application, and the use of different buffering agents in the copending application than the buffering agents (i.e., pH adjusting agents) used in the present application. In addition, pH is a controlling factor in these applications as to what is being prepared. The difference is based on (i) establishment of the equilibrium and (iii) the fact that the disulfide anion is undetectable at a pH of about 9 or less. [0012] Another way to view the difference is that when it is desired to make mercaptosilanes, rather than sulfidosilanes, the alkalinity of the reaction mixture must remain at a pH in the range of 4 to 9. Higher concentrations of alkalinity lead to disulfide anion formation from the mercaptide anion already present, without adding elemental sulfur. When it is desired to make the disulfide, it is necessary for the system to remain high in alkalinity, to inhibit any equilibrium leading to NaHS formation. As these reactants naturally react and form a neutral NaCl, the alkalinity of the brine will lessen over time, and can become low enough so that SH will form. [0013] So the present application differs from the copending application in that (i) different pH adjusting agents are employed, (ii) the pH is different, i.e., a pH of 4 to 9, preferably a pH of 5-8, and more preferably a pH of 5 to less than 7, instead of a pH of 7-14, and (iii) the order of addition of the reactants is not the same. The result is that at the lower pH of 4 to less than 7, any sulfide present is converted to mercaptan in the aqueous phase. [0014] The process of the present invention further differs from processes described above, in that it is capable of providing high yields of mercaptosilanes under mild conditions, without the use of solvents, toxic gas, and strictly anhydrous conditions. In addition, it is more economical, environment friendly, and capable of utilizing relatively inexpensive starting materials. When there is any byproduct present, it is simply an alkali metal salt, which can be easily removed by dissolution during the water and phase separation sequence of the process. [0015] Other advantages provided by the present invention over the prior art include the benefit that the mercaptoalkylalkoxy silane yield is significantly increased when chloroalkylalkoxysilanes are reacted with an aqueous solution of sodium hydrosulfide in the presence of (i) a phase transfer catalyst and (ii) gases which form an acidic solution in water to control the pH of the aqueous phase, at a pressure of 10-200 psi/69-1,380 kPa, preferably 25-100 psi/173-690 kPa. Some particularly suitable gases are hydrogen sulfide, carbon dioxide, and sulfur dioxide. The reaction can be carried out without requiring use of a solvent, and no extra salt is needed to saturate the aqueous phase to prevent hydrolysis of any alkoxy groups present on silicon atoms in the molecule. [0016] Most significantly, however, the order of addition of the reactants plays an important role in the product yield and quality. Thus, it was surprising to discover that the mercaptoalkylalkoxysilane yield can be increased when the NaHS solution is added to a mixture of the haloalkylalkoxysilane and the anhydrous phase transfer catalyst at the reaction temperature. In this regard, anhydrous pH adjusting salts may be required to be added to the organic reaction mixture before the NaHS addition, to control any potential side reactions. In those instances where it is desired to carry out the reaction under pressure conditions, the reactor is pressurized with H2S, CO2, and/or SO2, before addition of the NaHS to the haloalkylalkoxysilane/catalyst mixture. The anhydrous salt of a mineral acid and the phase transfer catalyst can then be mixed with the haloalkylalkoxysilane, before adding the sodium hydrosulfide. This feature will tend to minimize any hydrolysis of alkoxy groups on silicon. [0017] Lastly, the presence of side products of species such as 3,3'bis(triethoxysilylpropyl)monosulfide (TESPM) and 3,3'bis(triethoxysilylpropyl)disulfide (TESPD), are significantly reduced when mineral acids and their salts are used in the process. Thus, the acids and the pH adjusting agents having pH values of less than seven, react with disodium sulfide impurities in the aqueous solution of sodium hydrosulfide, and produce sodium hydrosulfide and hydrogen sulfide gas. The maintenance of a positive pressure of H2S in the existing headspace will prevent the formation of the sulfide species, by shifting the equilibrium between NaHS and sodium sulfide (Na2S), toward NaHS in the aqueous phase. [0018] This invention is directed to a process for making high purity mercaptoalkylalkoxysilanes using a phase transfer catalyst, by forming a mixture of (i) an haloalkylalkoxysilane and (ii) a phase transfer catalyst, prior to the addition of (iii) a sulfide compound such as sodium hydrosulfide. The reaction will occur without requiring that there be present in the haloalkylalkoxysilane phase, a concentrated sodium chloride salt solution with the sodium hydrosulfide, or an organic solvent. The formation of byproducts can also be reduced by the addition of certain pH adjusting agents having a pH of less than seven to the mixture containing the haloalkylalkoxysilane and the phase transfer catalyst. In particular, the process is directed to the reaction of an aqueous solution of sodium hydrosulfide with CPTES in the presence of a phase transfer catalyst, and a pH adjusting agent of a pH of 4 to 9, preferably a pH of 5-8, and more preferably a pH of 5 to less than 7. Thus, it was surprisingly discovered that both the order of addition of the reactants, and the addition of certain pH adjusting agents in the reaction mixture, significantly increased the yield of MPTES by minimizing formation of undesirable end products such as TESPM and TESPD. [0019] As an additional feature, the invention is directed to the use of certain pH adjusting agents which are acidic in their nature in an aqueous solution, such as SO2 (sulfur dioxide), CO2 (carbon dioxide), H2S (hydrogen sulfide), H3PO4 (phosphoric acid), H3BO3 (boric acid), and HCl (hydrochloric acid). These materials improve the yield by minimizing the production of any undesirable byproduct such as TESPM and TESPD. [0020] In a first embodiment of the process for making the mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. [0021] In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, and anhydrous salts thereof, are mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts. [0022] Following is a list of acronyms used in this application: CPTES - Chloropropyltriethoxysilane CPTMS - Chloropropyltrimethoxysilane MPT AS - Mercaptopropyltrialkoxysilane MPTES - Mercaptopropyltriethoxysilane TBAB - Tetrabutylammonium Bromide TBAC - Tetrabutylammonium Chloride TESPD - 3,3'bis(triethoxysilylpropyl)disulfide TESPM - 3,3'bis(triethoxysilylpropyl)monosulfide [0023] These and other features of the invention will become apparent from a consideration of the following detailed description. DETAILED DESCRIPTION OF THE INVENTION [0024] The synthesis of mercapto-functional alkoxysilanes is carried out via a reaction using a phase transfer catalysis process in an aqueous/organic medium. The use of small amounts of gases such as H2S, CO2, and SO2, as well as the use of the other pH adjusting agents of the invention which are all acidic in nature in the aqueous phase, during the reaction, minimizes the production of undesirable end products such as TESPM and TESPD. Therefore, the yield of a mercaptopropyltrialkoxysilane can be significantly increased to more than 90 percent. As noted, it was also surprisingly discovered that a positive pressure of H2S or CO2 during the reaction of (i) chloropropyltriethoxysilane with (ii) a sodium hydrosulfide solution and (iii) tetrabutylammonium bromide catalyst (TBAB) minimized TESPM and TESPD to less than 1.0 weight percent, compared to about 10 weight percent when no pressure was maintained. [0025] In this regard, it is believed that the H2S or CO2 pressure causes a reduction in the pH of the aqueous phase either by the dissolution of H2S, or there occurs an intermediate reaction of CO2 with H2O to form carbonic acid. In any event, at a reduced pH, the di- sodium sulfide impurities are converted to sodium hydrosulfide, and minimize TESPM formation. Thus, when a sodium hydrosulfide aqueous solution was added to a heated reactor pressurized with H2S gas and containing TBAB and CPTES, the organic phase after filtration included more than 90 weight percent of desired end product MPTES, and less than one weight percent of undesired species TESPM and TESPD. [0026] Accordingly, the first sequence of steps of the process involves mixing a phase transfer catalyst with an haloalkylalkoxysilane. Phase transfer catalysts suitable for use according to the invention are quaternary onium cations. Some representative examples of quaternary onium salts yielding quaternary ammonium cations that can be used as phase transfer catalysts are described in US 5,405,985 (April 11, 1995), among which are tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraphenylarsonium bromide, and tetraphenylarsonium chloride. The '985 patent is considered as being incorporated herein by reference. The preferred quaternary onium salts according to this invention are TBAB and TBAC, most preferably TBAB. These materials are available commercially from chemical suppliers such as Sigma-Aldrich, Milwaukee, Wisconsin. While the amount of phase transfer catalyst used in the process can vary, it is preferably used in an amount of 0.1-10 weight percent, most preferably 0.5-2 weight percent, based on the amount of haloalkylalkoxysilane being used in the process. [0027] Haloalkylalkoxysilanes for purposes of this invention are those organosilicon compounds having a structure generally corresponding to the formula (RO)3_mRmSi-Alk-X, wherein each R is an independently selected hydrocarbon group containing 1-12 carbon atoms, such as methyl, ethyl, propyl, butyl, isobutyl, cyclohexyl, or phenyl. Preferably, R is a methyl or ethyl group, m can be 0, 1, or 2, but preferably m is zero. Alk represents a divalent hydrocarbon group containing 1-18 carbon atoms, preferably 2-4 carbon atoms, such as ethylene, propylene, butylene, or isobutylene. Preferably, Alk is a propylene group. X is one of the halogen atoms, i.e., fluorine, chlorine, bromine, or iodine, preferably chlorine. Some representative examples of haloalkylalkoxysilanes suitable for use in this invention include chloropropyltriethoxysilane, chloropropyltrimethoxysilane, chloroethyltriethoxysilane, chlorobutyltriethoxysilane, chloroisobutylmethyldiethoxy silane, chloroisobutylmethyldimethoxysilane, and chloropropyldimethylethoxysilane. The haloalkylalkoxysilane compound most preferred is chloropropyltriethoxysilane. [0028] The second sequential step of the process is addition of a sulfide compound. The sulfide compound is a composition having a structure corresponding to the formula M2Sn or MHS, or mixtures thereof, wherein M represents an alkali metal or ammonium group, and H is hydrogen. While the alkali metal can be potassium, sodium, rubidium, or cesium, sodium is preferred. Representative of some preferred compositions of the type MHS include compositions such as NaHS, KHS, and NH4HS, with NaHS being most preferred. The NaHS composition can be used in the form of NaHS flakes containing 71.5-74.5 weight percent NaHS, or an NaHS liquor containing 45-60 weight percent NaHS. Such materials are available commercially from PPG Industries, Inc., Pittsburgh, Pennsylvania. Optionally, compositions of the type M2Sn can be used, when it is desired to avoid the necessity of dissolving solid or flake forms. Suitable compositions of this type include Na2S, K2S, Cs2S, (NH4)2S, Na2S2, Na2S3, Na2S4, Na2S6, K2S2 K2S3? K2S4, K2S6, and (NH4)2S2. A particularly preferred sulfide composition is a solution containing 25-72 weight percent of NaHS, preferably 45-60 weight percent NaHS, also available from PPG Industries, Inc., Pittsburgh, Pennsylvania. [0029] If desired, sulfur (S) can be added as an optional ingredient. A suitable sulfur is elemental sulfur in the form of an 100 mesh refined sulfur powder available from Sigma- Aldrich, Milwaukee, Wisconsin. While the amount of sulfur and sulfide compound can vary, it can be present in a molar ratio corresponding to S/M2Sn or S/MHS of 0 to 2.0, preferably zero. [0030] In the preferred embodiment, the phase transfer catalyst and haloalkylalkoxysilane are combined with a pH adjusting agent which is only slightly acidic in nature or one that is diluted to such an extent as to be only slightly acidic. The pH adjusting agent can be SO2 (sulfur dioxide), CO2 (carbon dioxide), H2S (hydrogen sulfide), H3PO4 (phosphoric acid), H3BO3 (boric acid), or HCl (hydrochloric acid). While the amount of pH adjusting agent added to the aqueous phase can vary, it is generally present in a molar amount of 0.01 to 1.0 mole per mole of M2Sn or MHS being used in the process, preferably 0.01 to 0.3 mole per mole of M2Sn or MHS being used in the process. [0031] The process is carried out in an aqueous/organic phase containing the haloalkylalkoxysilane, phase transfer catalyst, pH adjusting agent, and sulfide compound. While the amount of water used to create the aqueous phase can vary, it is preferably based on the amount of haloalkylalkoxysilane being used in the process. The water can be added directly, or it can be present indirectly, as the water present in small amounts in starting materials. In any case, the total amount of water for purposes of the invention should include all water added directly or indirectly. Accordingly, the total amount of water used to create the aqueous phase is 1-100 weight percent of the amount of haloalkylalkoxysilane being used in the process, preferably 2.5-70 weight percent, most preferably 20-40 weight percent. [0032] Although not being willing to be bound by any particular theory, it is believed that that the addition of only certain pH adjusting agents, i.e., the pH adjusting agents noted above, to the aqueous phase during the process, controls the pH of the reaction medium so as to directly affect product formation and minimizes any potential of undesired side reactions. Thus, the pH is controlled by addition of such pH adjusting agents at rates and concentrations so as to maintain the pH during the reaction in the range of 4 to 9, preferably in the range of 5-8, and more preferably in the range of 5 to less than 7. The haloalkylalkoxysilane compound is added to the aqueous phase at such a rate so as to control the exothermic reaction, and at the same time maintain a temperature in the range of 40-110 °C. Preferably the reaction temperature is maintained at 60-95 °C. The progress of the reaction can be monitored by determining the consumption of the haloalkylalkoxysilane. The amount of catalyst being used as well as the reaction temperature will affect the reaction time necessary for its completion. [0033] At the end of the reaction, a product mixture is produced containing an organic phase, an aqueous phase, and possibly some precipitated solid materials that includes salts formed during the reaction. The organic phase contains the mercaptoalkylalkoxysilane, and separation of the mercaptoalkylalkoxysilane from the product mixture can be obtained simply by phase separation of the organic phase from the aqueous phase, or if precipitated salts are formed during the reaction, the salts can be separated first by filtering or decanting prior to the phase separation. Water or a dilute acidic solution can be added to the product mixture prior to separation, as the addition of water or a dilute acidic solution tends to enhance phase separation by dissolving precipitated salts. [0034] The amount of water or dilute acidic solution added during this step can vary from 10-50 weight percent based on the weight of the haloalkylalkoxysilane, preferably 20-40 weight percent, and most preferably 25-35 weight percent. When a dilute acidic solution is used, it can contain HCl, HNO3, or H2SO4, for example, having normal (N) concentrations of 0.000001-5, preferably 0.01-1. The dilute acidic solution can also be prepared by adding a chlorosilane to water, i.e., =Si-Cl + H-OH ? ?Si-OH + HCl. [0035] Following addition of water or a dilute acidic solution to the product mixture, the mercaptoalkylalkoxysilane can be isolated from the product mixture by phase separating the organic phase from the aqueous phase. The organic phase containing the mercaptoalkylalkoxysilane can also be subjected to a drying step. One example of drying is to treat the organic phase under vacuum to remove any volatile organic materials present, along with the residual water. The drying can be to simply heat the organic phase to a temperature of 20-160 °C under a reduced pressure of 5-35 mm Hg (0.67 to 4.65 kPa), preferably 90-120 °C at 5-25 mm Hg (0.67 to 3.33 kPa). Alternatively, drying of the organic phase can be obtained using a thin film stripper to remove volatile organic materials as well as residual water in the organic phase. [0036] Yet another drying technique is to contact the organic phase containing the mercaptoalkylalkoxysilane with a desiccant. The desiccant can be any solid material known to be capable of removing trace quantities of water from organic phases. Representative desiccants are typically ionic hygroscopic compositions such as sodium sulfate, magnesium sulfate, as well as the silicate based compositions such as zeolites, silica, and alumina/silicates. Preferred desiccants are sodium sulfate or magnesium sulfate, and sodium sulfate is most preferred. [0037] The dried organic phase can then be subjected to additional steps to further improve its final purity and appearance. Thus, the organic phase containing the mercaptoalkylalkoxysilane can be heated under vacuum to strip low boiling components such as ethanol, water, tributylamine, and dissolved H2S gas, For example, the organic phase, when heated to 30-100 °C at 10-200 mm Hg/1.3-27 kPa vacuum, provides a clear product which has a better shelf life. The organic phase, after stripping the low boiling components can also be distilled under high vacuum, i.e., 1-20 mm Hg/0.133-2.7 kPa, to provide highly pure mercaptoalkylalkoxysilanes. As a result, the long-term storage stability of the mercaptoalkylalkoxysilane is enhanced, i.e., the composition does not change with time or result in products containing undesirable solid precipitates. [0038] The following examples are set forth to illustrate the invention in more detail. In particular, they teach those skilled in the art how to obtain the primary benefits of the present invention, i.e., increase the yield of MPTES and reduce side product species such as TESPM and TESPD. [0039] The purpose of this example is to show no reduction in TESPM formation when none of the pH adjusting agents of the invention are employed. Thus, in a three neck round bottom flask equipped with an addition funnel, condenser, stirrer and thermometer, was added with 100 g (1.26 moles) of NaHS flakes containing 61.7 percent by weight NaHS and 6.07 weight percent Na2S, and 75.62 g of deionized (DI) water. The mixture was heated to 70 °C and mixed to make a bright yellow solution of NaHS. Then, 9.0 g (0.0094 mole) tetrabutylammonium bromide solution containing 25 weight percent active was added and mixed. The color of the mixture changed to dark brown, and an oily layer of catalyst intermediate formed at the interface. Then 317.6 g (1.32 mole) chloropropyltriethoxysilane was added slowly in 8 minutes while mixing at 500 rpm. The reaction temperature increased to 82 °C due to an exotherm. The reaction was carried out for 3 hours at 80 °C, and 139.6 g of deionized water was added after cooling the mixture to 50 °C to dissolve the sodium chloride salt byproduct. After conducting a phase separation, 287.7 g of an organic phase was collected. It contained 8.4 weight percent of unreacted CPTES, 61.7 weight percent of mercaptopropyltriethoxysilane, 9.6 weight percent of TESPM, and 17.82 weight percent of TESPD, as determined by Gas Chromatograhy (GC) analysis. [0040] This example is the reverse of Example 1, and shows that the product gelled. Thus, the order of addition in Example 1 was reversed, and a solution of sodium hydrosulfide flake was prepared by adding 76.2 g of water to 100.11 g of sodium hydrosulfide flakes. The solution was added slowly via an addition funnel to a reaction mixture containing 317.6 g of chloropropyltriethoxysilane and 3.1 g of solid tetrabutylammonium bromide at 67 °C. The reaction mixture gelled within 5 minutes of the NaHS addition. [0041] The purpose of this example is to show that while the addition of sulfur reduced the formation of TESPM, the formation of TESPD increased. Thus, in a similar reaction to the one in Example 1, the ratio of sulfur to NaHS was increased to 0.05 to convert the TESPM into TESPD. NaHS flakes (146.3 g., 1.83 mole), sulfur (2.92 g, 0.092 mole), and 100 g DI water, were mixed in a glass-jacketed reactor and heated to 70 °C. TBAB solution (14.4 g, 0.011 mole) was added and mixed. Instantly, an oily omega phase was formed at the surface. CPTES (400 g, 1.66 mole) was added at a rate of about 30 ml/min. The reaction temperature increased to 94 °C due to the exotherm, and some gel was observed in the organic phase. 380.1 g (95 percent by weight of CPTES) organic phase was collected after a three hour reaction. The gas chromatography analysis showed 1.5 percent CPTES, 66.7 percent MPTES, 3.37 percent TESPM, and 27.9 percent TESPD. [0042] This example is the same as Example 3 except that a salt was added so that no gelation would occur in the organic phase. However, while the formation of TESPM was reduced, the formation of TESPD increased. Accordingly, an excess amount of NaHS flakes were used, and NaCl salt was added to saturate the aqueous phase before the addition of CPTES. The sulfur/NaHS ratio was 0.05. The catalyst solution was also added after the CPTES addition was completed. Thus, NaHS flakes (100 g., 1.248 mole), NaCl 87.7 g, sulfur (2.0 g, 0.063 mole), and 161.5 g of water, were mixed and heated to 60 °C. CPTES (161.5 g., 0.671 mole) was added slowly and mixed at 300 rpm. A 25 weight percent solution of TBAB catalyst was added to the reaction mixture at 65 °C. A slight exotherm was observed, and the reaction was completed in about 5 hours. The GC analysis of the organic phase showed that it contained 0.35 weight percent CPTES, 62.2 weight percent MPTES, 1.1 weight percent TESPM, and 34.1 weight percent TESPD. The product was stable. The MPTES yield was less due to side reactions when sodium hydrosulfide flakes were used. [0043] This example shows the benefits obtained by using a solution of NaHS instead of NaHS flakes. In this example, the yield of MPTES was increased while the amount of the TESPM and TESPD byproducts decreased, by using the NaHS solution. Thus, NaHS flakes were replaced with a solution containing 45 weight percent of NaHS. No additional water was used in the aqueous phase as the NaHS solution contained water. Thus, a solution containing 45 weight percent NaHS (143 g., 1.15 mole) and 50 weight percent of a TBAB solution (99.6 g, 0.015 mole) were added into a glass reactor, mixed, and heated to 70 °C. CPTES (240.8 g., 1.0 mole) was slowly added to maintain the reaction temperature below 80 °C. After 5 hours, the reaction mixture was cooled to room temperature, and water was added to dissolve the NaCl salt in the aqueous phase. 229 g. of a light yellow organic phase was collected (95 weight percent based on CPTES), and analyzed. The GC analysis showed that it contained 1.6 weight percent CPTES, 84 weight percent MPTES, 6.9 weight percent TESPM, and 1.4 weight percent TESPD. No gel was found in the product. Color in the product was removed by treating it with 1-2 weight percent activated carbon black and clay. [0044] The NaHS/CPTES ratio in this example was changed from 1.15 to 1.30. All other conditions were similar to Example 5. An increase in rate of reaction was observed with an increase in NaHS concentration in the reaction mixture. No significant change was observed in the product composition. The reaction was completed in 3 hours. The GC analysis results showed 0.8 weight percent CPTES, 82.3 weight percent MPTES, 6.6 weight percent TESPM, and 0.8 weight percent TESPD. [0045] Example 6 was repeated, except the order of addition of the reactants was reversed. Thus, CPTES (240.8 g., 1.0 mole) and solid TBAB (4.82 g., 0.015 mole) were added into a glass reactor, mixed, and heated to 70 °C. A solution containing 45 weight percent NaHS (160.4 g., 1.30 mole) was added using an addition funnel in about 20 minutes. A slight exotherm was observed during the initial addition of NaHS. The reaction was stopped after 4 hours, and the byproduct NaCl was dissolved in water. The organic phase recovered after the phase separation was 225.5 g. (93.6 weight percent based on CPTES). The product composition by GC analysis showed that it contained 0.83 weight percent CPTES, 84.2 weight percent MPTES, 6.79 weight percent TESPM, and 0.7 weight percent TESPD. There was a slight improvement in MPTES yield by changing the order of addition of the sodium hydrosulfide. The GC analysis also showed a lower content of hydrolyzed oligomers than the GC analysis in Example 6. [0046] The purpose of this example is to further minimize the TESPM formation and to increase the MPTES yield. Accordingly, an HCl solution was added dropwise to an NaHS solution during its reaction with CPTES at atmospheric pressure. Hydrogen sulfide gas formed in the reaction was neutralized in a caustic scrubber. 150.1 g (1.2 mole) of a 45 percent by weight NaHS solution, and 9.63 g (0.015 mole) of a 50 percent by weight TBAB catalyst solution, was added to the reactor, mixed, and heated to 65 °C. 100 g (0.15 mole) of a 1.3 molar HCl solution, and 240.0 g (1.0 mole) of CPTES, were added simultaneously from two addition funnels, at a rate such that the addition of CPTES was completed in 15 minutes, and the addition of HCl was complete in about an hour. The reaction was continued at 70 °C for 5 hours. GC data showed 11.4 weight percent of unreacted CPTES remaining, and therefore 12.48 g (0.1002 mole) of an NaHS solution was again added and reacted for 5 hours. The organic phase was separated after cooling and filtered through a 0.45 micron filter disc. Gas chromatographic (GC) analysis of the organic phase showed that the product contained 2.6 weight percent of CPTES, 91.0 weight percent of MPTES, 1.99 weight percent of TESPM, and 2.34 weight percent of TESPD. [0047] A 50 percent by weight solution of NaHSC4 was added to an NaHS solution during its reaction with CPTES. 325 g (2.69 mole) of an NaHS solution, and 8.2 g (0.0124 mole) of a TBAB solution, were added to a glass reactor, mixed, and heated to 75 °C. The addition dropwise of NaHSO4 solution was initiated just prior to the addition of CPTES. 497.8 g (2.07 mole) of CPTES was added to the reaction mixture in 8 minutes. The addition of the NaHSO4 solution was complete in 30 minutes. The organic phase was separated after a 5 hour reaction and analyzed by GC. The product contained 2.0 percent by weight of CPTES, 87.6 percent by weight of MPTES, 2.7 percent by weight of TESPM, and 0.7 percent by weight of TESPD. The product was distilled under vacuum to provide a 95.4 percent pure MPTES at a yield of about 84 percent, based on the amount of CPTES employed. [0048] Boric acid was used in this example to lower the pH of the reaction mixture. The order of addition of CPTES and NaHS as compared to Example 10 was also reversed to minimize any potential formation of a gel. Thus, 206.3 g (0.86 mole) of CPTES, 4.13 g (0.013 mole) of solid TBAB, and 51.4 g (0.83 mole) of H3BO3, were mixed in ajacketed glass reactor and heated to 65 °C. 100.0 g (0.83 mole) of an NaHS solution was slowly added with a dropping funnel over a time interval of 30 minutes. Froth and foaming were observed due to the reaction of NaHS and boric acid. Additional NaHS solution and TBAB catalyst were added after reaction with CPTES for 3-4 hours. After a total reaction time of 6 hours, the reaction mixture was cooled, filtered, and phase separated. The product composition by GC analysis was determined to be 1.2 percent by weight of CPTES, 89.3 percent by weight of MPTES, 2.8 percent by weight of TESPM, and 0.2 percent by weight of TESPD. [0049] Sodium di-hydrogen phosphate monohydrate was used as a pH adjusting agent in this example to reduce the formation of TESPM in the product. Thus, 27.6 g (0.2 mole) of NaH2PO4.H2O was added to a reactor. 157.4 g (1.30 mole) of a 45 percent by weight solution of NaHS was slowly added to avoid any violent reaction between NaHS and dihydrogen phosphate. H2S gas was evolved from the reaction, and was trapped in a caustic scrubber. 9.63 g (0.015 mole) of a TBAB solution was added, and mixed for 5 minutes. A very dark green omega phase of a catalyst intermediate formed instantly. The reaction mixture was slowly heated to 70 °C, and 240.8 g (1.0 mole) of CPTES was added over 15 minutes. The reaction was continued for 4 hours at 70 °C. Upon its cooling and phase separation, a 227.6 gram organic phase was obtained. The organic phase yield was 94.5 percent, based on the amount of CPTES used in the reaction. GC results of the organic phase showed 2.8 percent of CPTES, 89.6 percent of MPTES, 4.5 percent of TESPM, and 1.15 percent of TESPD. [0050] In this example, sodium acetate trihydrate was mixed with an NaHS solution to reduce the pH of the aqueous phase and to minimize the formation of TESPM. Thus, equimolar amounts of sodium acetate and NaHS were added to a reactor and mixed. No change in the pH was observed. The reaction was carried out using a slight molar excess of CPTES, and in the presence of the TBAB catalyst, as described above in Examples 8-11. GC results of the final product showed no effect on TESPM reduction, however. The product contained 83.1 percent by weight of MPTES and 7.38 percent by weight of TESPM. [0051] In the following examples, a series of experiments were performed using H2S as pH adjusting agent, at different H2S pressure, to control the pH of reaction mixture and improve the yield of MPTES. [0052] A pressure reactor containing NaHS solution was pressurized with H2S gas to 10 psi at room temperature before reacting it with CPTES in presence of a TBAB catalyst. The H2S gas in water had a pH of 4.2, and reacted with Na2S byproducts in the aqueous phase to provide NaHS. It also prevented Na2S formation by maintaining the pH below 9. The positive pressure of H2S during the reaction also minimized hydrolysis of any alkoxy groups and polymer formation [0053] Thus, 139.4 g (1.15 mole) of NaHS solution was added to the reactor and the reactor was sealed. The reactor was then charged with 10 psi/69 kPa H2S and the contents were mixed for 5 minutes. A pressure drop was initially observed due to the H2S solubility in water and its reaction with Na2S. The NaHS was heated to 70 °C, and 9.6 g (0.015 mole) of a 50 weight percent solution of TBAB and 240.8 g (1.0 mole) of CPTES were fed consecutively into the reactor using a pressure syringe. The reaction was continued for 3.5 hours at 80 °C before being cooled. Deionized water was added to the reaction mixture to dissolve any NaCl salt byproduct, and the organic phase was recovered by phase separation. The GC composition consisted of 1.8 weight percent of CPTES, 87.5 weight percent of MPTES, 4.6 weight percent of TESPM, and 1.5 weight percent of TESPD. The yield was 90 percent. [0054] Except for the 50 psi/345 kPa H2S pressure, all other conditions were the same as Example 13. The reaction was completed in 5 hours. The product composition was 0.4 weight percent of CPTES, 93.0 weight percent of MPTES, 1.9 weight percent of TESPM, and 0.08 weight percent of TESPD. The product yield was 93.3 percent. [0055] Except for the 100 psi/690 kPa H2S pressure, all other conditions were the same as Examples 13 and 14. The product composition after a 5 hour reaction was 0.5 weight percent of CPTES, 89.8 weight percent of MPTES, 0.8 weight percent of TESPM, and 0.3 weight percent of TESPD. The yield was 95.3 percent. It can be seen that the yield of MPTES was improved by suppressing any byproduct formation through control of the pH by the H2S gas. [0056] This example is the same as Example 14 except that the order of addition of the reactants is reversed. Also, a solid TBAB catalyst was used to avoid the hydrolysis of CPTES. Thus, 240.8 g (1.0 mole) of CPTES and 4.8 g (0.015 mole) of solid TBAB catalyst were loaded into a pressure reactor and the reactor was sealed. The reactor was pressurized with H2S until the pressure stabilized at 50 psi/345 kPa. The H2S valve was closed, and the reaction mixture was heated to 70 °C while mixing the contents at 500 rpm. 139.2 g (1.15 mole) of an NaHS solution was then slowly added to the reactor at a rate of about 10 ml/min using a pressure syringe pump. The reaction temperature increased to 80 °C due to the exothermic reaction. After 5 hours of reaction at 80°C, the mixture was cooled to 30 °C and any salt byproducts were dissolved in 69 g of deionized water. Upon cooling and phase separation, a 229 gram organic phase was obtained. The organic phase yield was 95.4 percent based on the amount of CPTES used in the reaction. GC results of the organic phase showed 0.9 percent of CPTES, 93.3 percent of MPTES, 0.4 percent of TESPM, and 1.0 percent of TESPD. Thus, it can be seen that the yield of MPTES was increased when H2S gas was used in this example of a reverse addition process. [0057] In the following examples, a series of experiments were performed using CO2 as the pH adjusting agent, at different CO2 pressure, to control the pH of reaction mixture and improve the yield of MPTES. [0058] A pressure reactor containing an NaHS solution was pressurized with CO2 gas to 25 psi/173 kPa at room temperature before reacting it with CPTES in presence of a TBAB catalyst. The CO2 gas in water was slightly acidic due to the formation of carbonic acid, which in turn reacts with any Na2S byproduct in the NaHS solution to minimize TESPM formation, and to improve the overall yield of MPTES. Maintaining a positive pressure of CO2 during the reaction also minimized any hydrolysis of alkoxy groups and polymer formation. [0059] Thus, and similar to Example 12, 139.2 g (1.15 mole) of an NaHS solution was charged to the pressure reactor and the reactor was sealed. 10 psi/69 kPa CO2 pressure was applied and the contents were mixed for 5 minutes. The reaction mixture was heated to 70 °C and 9.6 g (0.015 mole) of aTBAB solution and 240.8 g (1.0 mole) of CPTES were added to the reactor by a pressure syringe at a controlled rate. The reaction was continued for 5 hours at 80 °C. The progress of the reaction was monitored by the GC analysis of the organic phase and the consumption of CPTES. After cooling the reaction mixture and phase separation, the organic phase was stripped to remove any low boilers and analyzed by GC. The product contained 0.3 weight percent of CPTES, 92.1 weight percent of MPTES, 2.3 weight percent of TESPM, and 0.5 weight percent of TESPD. The yield was 91.1 percent based on the amount of CPTES used. [0060] Except for CO2 pressure being increased to 50 psi/345 kPa, all other conditions were the same as Example 16. After phase separation, the organic phase was analyzed by GC, and it contained 0.5 weight percent of CPTES, 88.8 weight percent of MPTES, 1.3 weight percent of TESPM, and 2.6 weight percent of TESPD. Similar good results were obtained when the CO2 was continuously fed to the reactor during a reaction at 50 psi/345 kPa. [0061] Example 18 was repeated, except that the reaction was performed at 100 psi/690 kPa CO2 pressure. The pressure increased to 135 psi/932 kPa when the reaction mixture was heated to 70 °C. The pressure dropped during the CPTES addition as the NaHS was consumed in the reaction. The organic phase was isolated after completion of the reaction and analyzed. The product contained 2.3 weight percent of CPTES, 88.2 weight percent of MPTES, 0.9 weight percent of TESPM, and 2.8 weight percent of TESPD. Color in the product was removed by treatment with activated carbon black. [0062] Example 16 was repeated, except that the reaction was carried out under a 50 psi/345 kPa CO2 gas pressure. NaCl and NaHCO3 salts were produced in the reaction. Upon cooling and phase separation, a 222.8 gram organic phase was obtained. The organic phase yield was 92.8 percent based on the amount of CPTES used in the reaction. GC results of the organic phase showed 0.8 percent of CPTES, 92.4 percent of MPTES, 1.2 percent of TESPM, and 0.5 percent of TESPD. [0063] The organic phase was also distilled under vacuum, and the product was collected at 68 °C/1 mm Hg/0.133 kPa. After complete distillation, a small amount of solid polymer residue remained in the pot. The distillate contained 0.9 weight percent of CPTES and 98.0 weight percent of MPTES. [0064] Other variations may be made in compounds, compositions, and methods described herein without departing from the essential features of the invention. The embodiments of the invention specifically illustrated herein are exemplary only and not intended as limitations on their scope except as defined in the appended claims. We claim: 1. A process for making mercaptoalkylalkoxysilanes comprising the sequential steps of: first, mixing (i) a pH adjusting agent and (ii) a sulfide containing compound of the formula M2Sn or MHS where M is an alkali metal or an ammonium group and H is hydrogen, in an aqueous phase, to provide a pH in the range of 4-9 of the aqueous phase, second, adding (iii) a phase transfer catalyst to the aqueous phase, third, adding (iv) a haloalkylalkoxysilane to the aqueous phase, to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and Fourth, separating the desired mercaptoalkylalkoxysilanes from the water soluble byproducts. 2. The process according to Claim 1 in which the pH adjusting agent is sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, or hydrochloric acid. 3. The process according to Claim 2 in which the pH adjusting agent is carbon dioxide or hydrogen sulfide. 4. The process according to Claim 3 in which the pressure of the carbon dioxide or hydrogen sulfide is 10-200 psi/69-1,380 kPa. 5. The process according to Claim 4 in which the pressure is 25-100 psi/173-690 kPa. 6. The process according to Claim 1 in which the pH in the aqueous phase is 5-8. 7. The process according to Claim 6 in which the pH in the aqueous phase is 5 to less than 7. 8. The process according to Claim 1 in which the reaction temperature is 40-110 °C. 9. The process according to Claim 8 in which the reaction temperature is 60-95 °C. 10. The process according to Claim 1 in which the haloalkylalkoxysilane has the formula (RO)3-mRmSi-Alk-X wherein each R is a hydrocarbon group containing 1-12 garbon atoms; m is 0, 1, or 2; Alk represents a divalent hydrocarbon group containing 1-18 carbon atoms; and X is chlorine, bromine, or iodine. 11. The process according to Claim 10 in which the haloalkylalkoxysilane is chloropropyltriethoxysilane, chloropropyltrimethoxy silane, chloroethyltriethoxysilane, chlorobutyltriethoxy silane, chloroisobutylmethyldiethoxysilane, chloroisobutylmethyldimethoxy silane, or chloropropyldimethylethoxysilane. 12. The process according to Claim 11 in which the haloalkylalkoxysilane is chloropropyltriethoxysilane. 13. The process according to Claim 1 in which the sulfide-containing compound is sodium hydrosulfide, potassium hydrosulfide, or ammonium hydrosulfide, disodium sulfide, dipotassium sulfide or diammonium sulfide. 14. The process according to Claim 13 in which the sulfide-containing compound is sodium hydrosulfide. 15. The process according to Claim 14 in which the sodium hydrosulfide is an aqueous solution containing 25-72 percent of sodium hydrosulfide. 16. The process according to Claim 15 in which the aqueous solution contains 40-50 percent of sodium hydrosulfide. 17. The process according to Claim 1 in which the phase transfer catalyst is a quaternary onium salt. 18. The process according to Claim 17 in which the phase transfer catalyst is tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraphenylarsonium bromide, or tetraphenylarsonium chloride. 19. The process according to Claim 18 in which the phase transfer catalyst is tetrabutylammonium bromide. 20. The process according to Claim 1 in which the aqueous phase is saturated with sodium chloride. 21. The process according to Claim 1 in which the aqueous phase in the first step of the process is free of sodium chloride. 22. A process for making mercaptoalkylalkoxysilanes comprising the sequential steps of: first, mixing together (i) a haloalkylalkoxysilane, (ii) a phase transfer catalyst, and (iii) an anhydrous pH adjusting agent, second, adding an aqueous solution of a sulfide containing compound or mixture of compounds of the formula M2Sn or MHS where M represents an alkali metal or ammonium group and H represents hydrogen, to form an aqueous reaction mixture with a pH in the range of 4-9 containing mercaptoalkylalkoxysilanes and water soluble byproducts, and third, separating the desired mercaptoalklyalkoxysilanes from the water soluble byproducts. 23. The process according to Claim 22 in which the pH adjusting agent is sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, or hydrochloric acid. 24. The process according to Claim 23 in which the pH adjusting agent is carbon dioxide or hydrogen sulfide. 25. The process according to Claim 24 in which the pressure of the carbon dioxide or hydrogen sulfide is 10-200 psi/69-1,380 kPa. 26. The process according to Claim 25 in which the pressure is 25-100 psi/173-690 kPa. 27. The process according to Claim 22 in which the pH is 5-8. 28. The process according to Claim 27 in which the pH is 5 to less than 7. 29. The process according to Claim 22 in which the reaction temperature is 40-110 °C. 30. The process according to Claim 29 in which the reaction temperature is 60-95 °C. 31. The process according to Claim 22 in which the haloalkylalkoxysilane has the formula (RO)3-mRmSi-Alk-X wherein each R is a hydrocarbon group containing 1-12 carbon atoms; m is 0, 1, or 2; Alk represents a divalent hydrocarbon group containing 1-18 carbon atoms; and X is chlorine, bromine, or iodine. 32. The process according to Claim 31 in which the haloalkylalkoxysilane is chloropropyltriethoxysilane, chloropropyltrimethoxy silane, chloroethyltriethoxysilane, chlorobutyltriethoxy silane, chloroisobutylmethyldiethoxysilane, chloroisobutylmethyldimethoxy silane, or chloropropyldimethylethoxysilane. 33. The process according to Claim 32 in which the haloalkylalkoxysilane is chloropropyltriethoxysilane. 34. The process according to Claim 22 in which the sulfide-containing compound is sodium hydrosulfide, potassium hydrosulfide, or ammonium hydrosulfide, disodium sulfide, dipotassium sulfide or diammonium sulfide. 35. The process according to Claim 34 in which the sulfide-containing compound is sodium hydrosulfide. 36. The process according to Claim 35 in which the aqueous solution contains 25-72 percent of sodium hydrosulfide. 37. The process according to Claim 36 in which the aqueous solution contains 40-50 percent of sodium hydrosulfide. 38. The process according to Claim 22 in which the phase transfer catalyst is a quaternary onium salt. 39. The process according to Claim 38 in which the phase transfer catalyst is tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraphenylarsonium bromide, or tetraphenylarsonium chloride. 40. The process according to Claim 39 in which the phase transfer catalyst is tetrabutylammonium bromide. 41. The process according to Claim 22 in which the aqueous reaction mixture is saturated with sodium chloride. 42. The process according to Claim 22 in which the mixture in the first step of the process is free of sodium chloride. In a first embodiment of a process for making mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, are mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts.

Full Text

METHOD OF MAKING MERCAPTOALKYLALKOXYSILANES
[0001] This invention relates to the synthesis of mercapto-functional organosilicon
compounds =Si-(CH2)nSH, more particularly mercaptoalkylalkoxysilanes such as
mercaptopropyltrialkoxy silane (MPTAS), using phase transfer catalysts. The process is
capable of producing high purity mercaptopropyltriethoxysilane (MPTES), for example.
Mercaptoalkylalkoxysilanes made by the process generally have a formula corresponding to
Z-Alk-SH in which Z is one of a group consisting of—SiR12R2, —SiR1R22, and—SiR23;
in which R1 is an alkyl group with 1-12 carbon atoms, a cyclohexyl group, or a phenyl group;
R2 is an alkoxy group containing 1-12 carbon atoms; and Alk represents a divalent
hydrocarbon radical having 1-18 carbon atoms and containing no unsaturation.
[0002] Sulfur containing organosilicon compounds are known to be useful as reactive
coupling agents between rubber and silica fillers, for improving the properties of cured
rubber. They are also known to be useful as adhesion promoters, for adhering rubber
compositions to substrates such as glass and metal. However, many sulfur containing
organosilicon compounds are difficult to make in good yield, because undesirable byproducts
are produced from various side reactions occurring when traditional methods are employed.
[0003] For example, US Patent 3,590,065 (June 29, 1971) relates to a reaction between a
haloalkylalkoxysilane and a thio-urea in the presence of ammonia. However, the necessity of
handling bulky by-products such as guanidine hydrochloride is the major disadvantage
associated with this particular method.
[0004] US Patent 3,849,471 (November 19, 1974) is directed to another method involving
reactions between haloalkylalkoxysilanes and hydrogen sulfide gas in the presence of amines.
However, this reaction is carried out under a high pressure, and also has the disadvantage of
producing a fluffy by-product salt which is difficult to filter from the end product.
[0005] US Patent 3,890,213 (June 17, 1975) relates to yet another method involving
reactions between hydrogen sulfide and alkenylalkoxysilanes. However, the major
disadvantage associated with this method is that the mercaptosilane product itself can become
associated with the alkenylalkoxysilane to form copious amounts of sulfide side products.
[0006] In British Patent 1,102,251 (February 7, 1968), a method is described involving the
reaction of sodium methoxide and hydrogen sulfide to produce sodium hydrosulfide, which is
then further reacted with an haloalkylalkoxysilane. The disadvantage associated with this
particular method however, is that the reaction of sodium methoxide with H2S produces
sodium sulfide as a by-product, which in turn leads to large amounts of polysulfide silanes in
the end product.
[0007] US Patent 5,583,245 ((December 10, 1996) describes a process for making
compounds generally corresponding to the formula Z-Alk-Sn-Alk-Z, in which Z and Alk are
the same as defined above, and in which n is 2-8. According to the process in the '245 patent,
a compound of the formula Z-Alk-X where X is chlorine or bromine, is reacted with an
ammonium hydrosulfide or an alkali metal hydrosulfide, and sulfur, using a phase transfer
catalyst, in an aqueous phase.
[0008] The '245 patent teaches that an additional reactant corresponding to Alk-X may be
present, where an unsymmetrical compound corresponding to Alk-Sn-Alk-Z is desired, in
addition to bis type end products. While the '245 patent does describe a method for preparing
MPTES in a 64.9 % yield by reacting (i) sodium hydrosulfide flakes and (ii)
chloropropyltriethoxysilane (CPTES), in a saturated sodium chloride solution and toluene
solvent, in the presence of a phase transfer catalyst, the yield of MPTES was not optimal.
[0009] While US Patent 5,840,952 ((November 24, 1998) describes a method of making
mercaptopropylalkoxysilanes in good yield, by purging hydrogen sulfide gas in a sodium
sulfide solution in methanol, and then reacting it with chloropropyltrimethoxysilane
(CPTMS) in an anhydrous system, the disadvantage associated with this process is that
sodium sulfide used must first be dehydrated. Another disadvantage of the '952 patent is that
it requires the use of high pressure, i.e., 600 psi/4,140 kilopascal (kPa) hydrogen sulfide gas,
to reduce sodium sulfide to sodium hydrosulfide.
[0010] In a prior copending application assigned to the same assignee as the present
invention, i.e., US Patent Application Serial No. 09/895,719, filed June 29, 2001, and entitled
"Preparation of Sulfur Containing Organosilicon Compounds Using a Buffered Phase
Transfer Catalysis Process", there is described a process based on phase transfer catalysis.
However, this process is directed to the production of bis-type sulfido silanes ?Si-S-Si?,
which generally correspond to the formula (RO)3_mRmSi-Alk-Sn-Alk-SiRm(OR)3-m,
wherein R is a monovalent hydrocarbon group with 1-12 carbon atoms; Alk represents a
divalent hydrocarbon group with 1-18 carbon atoms; m is 0-2; and n is 1-8. According to the
process described in the copending application, (A) a sulfide compound M2Sn or MHS
wherein H is hydrogen, M is ammonium or an alkali metal, and n is as defined above, is
reacted with (B) a silane compound corresponding to (RO)3-mRmSi-Alk-X, wherein X is Cl,
Br or I, m is the same as defined above, and (C) sulfur, in the presence of a phase transfer
catalyst, in an aqueous phase containing a buffering agent. However, no method is described
in the copending application for making mercapto-functional organosilicon compounds, i.e.,
compounds containing the group =Si-(CH2)nSH.
[0011] The copending application, however, results in sulfidosilanes instead of
mercaptosilanes. This is because of the presence of elemental sulfur in the copending
application, and the use of different buffering agents in the copending application than the
buffering agents (i.e., pH adjusting agents) used in the present application. In addition, pH is
a controlling factor in these applications as to what is being prepared. The difference is based
on (i) establishment of the equilibrium

and (iii) the fact that the disulfide anion is undetectable at a pH of about 9 or less.
[0012] Another way to view the difference is that when it is desired to make
mercaptosilanes, rather than sulfidosilanes, the alkalinity of the reaction mixture must remain
at a pH in the range of 4 to 9. Higher concentrations of alkalinity lead to disulfide anion
formation from the mercaptide anion already present, without adding elemental sulfur. When
it is desired to make the disulfide, it is necessary for the system to remain high in alkalinity,
to inhibit any equilibrium leading to NaHS formation. As these reactants naturally react and
form a neutral NaCl, the alkalinity of the brine will lessen over time, and can become low
enough so that SH will form.
[0013] So the present application differs from the copending application in that (i) different
pH adjusting agents are employed, (ii) the pH is different, i.e., a pH of 4 to 9, preferably a pH
of 5-8, and more preferably a pH of 5 to less than 7, instead of a pH of 7-14, and (iii) the
order of addition of the reactants is not the same. The result is that at the lower pH of 4 to less
than 7, any sulfide present is converted to mercaptan in the aqueous phase.
[0014] The process of the present invention further differs from processes described above,
in that it is capable of providing high yields of mercaptosilanes under mild conditions,
without the use of solvents, toxic gas, and strictly anhydrous conditions. In addition, it is
more economical, environment friendly, and capable of utilizing relatively inexpensive
starting materials. When there is any byproduct present, it is simply an alkali metal salt,
which can be easily removed by dissolution during the water and phase separation sequence
of the process.
[0015] Other advantages provided by the present invention over the prior art include the
benefit that the mercaptoalkylalkoxy silane yield is significantly increased when
chloroalkylalkoxysilanes are reacted with an aqueous solution of sodium hydrosulfide in the
presence of (i) a phase transfer catalyst and (ii) gases which form an acidic solution in water
to control the pH of the aqueous phase, at a pressure of 10-200 psi/69-1,380 kPa, preferably
25-100 psi/173-690 kPa. Some particularly suitable gases are hydrogen sulfide, carbon
dioxide, and sulfur dioxide. The reaction can be carried out without requiring use of a
solvent, and no extra salt is needed to saturate the aqueous phase to prevent hydrolysis of any
alkoxy groups present on silicon atoms in the molecule.
[0016] Most significantly, however, the order of addition of the reactants plays an
important role in the product yield and quality. Thus, it was surprising to discover that the
mercaptoalkylalkoxysilane yield can be increased when the NaHS solution is added to a
mixture of the haloalkylalkoxysilane and the anhydrous phase transfer catalyst at the reaction
temperature. In this regard, anhydrous pH adjusting salts may be required to be added to the
organic reaction mixture before the NaHS addition, to control any potential side reactions. In
those instances where it is desired to carry out the reaction under pressure conditions, the
reactor is pressurized with H2S, CO2, and/or SO2, before addition of the NaHS to the
haloalkylalkoxysilane/catalyst mixture. The anhydrous salt of a mineral acid and the phase
transfer catalyst can then be mixed with the haloalkylalkoxysilane, before adding the sodium
hydrosulfide. This feature will tend to minimize any hydrolysis of alkoxy groups on silicon.
[0017] Lastly, the presence of side products of species such as
3,3'bis(triethoxysilylpropyl)monosulfide (TESPM) and 3,3'bis(triethoxysilylpropyl)disulfide
(TESPD), are significantly reduced when mineral acids and their salts are used in the process.
Thus, the acids and the pH adjusting agents having pH values of less than seven, react with
disodium sulfide impurities in the aqueous solution of sodium hydrosulfide, and produce
sodium hydrosulfide and hydrogen sulfide gas. The maintenance of a positive pressure of
H2S in the existing headspace will prevent the formation of the sulfide species, by shifting
the equilibrium between NaHS and sodium sulfide (Na2S), toward NaHS in the aqueous
phase.
[0018] This invention is directed to a process for making high purity
mercaptoalkylalkoxysilanes using a phase transfer catalyst, by forming a mixture of (i) an
haloalkylalkoxysilane and (ii) a phase transfer catalyst, prior to the addition of (iii) a sulfide
compound such as sodium hydrosulfide. The reaction will occur without requiring that there
be present in the haloalkylalkoxysilane phase, a concentrated sodium chloride salt solution
with the sodium hydrosulfide, or an organic solvent. The formation of byproducts can also be
reduced by the addition of certain pH adjusting agents having a pH of less than seven to the
mixture containing the haloalkylalkoxysilane and the phase transfer catalyst. In particular, the
process is directed to the reaction of an aqueous solution of sodium hydrosulfide with CPTES
in the presence of a phase transfer catalyst, and a pH adjusting agent of a pH of 4 to 9,
preferably a pH of 5-8, and more preferably a pH of 5 to less than 7. Thus, it was surprisingly
discovered that both the order of addition of the reactants, and the addition of certain pH
adjusting agents in the reaction mixture, significantly increased the yield of MPTES by
minimizing formation of undesirable end products such as TESPM and TESPD.
[0019] As an additional feature, the invention is directed to the use of certain pH adjusting
agents which are acidic in their nature in an aqueous solution, such as SO2 (sulfur dioxide),
CO2 (carbon dioxide), H2S (hydrogen sulfide), H3PO4 (phosphoric acid), H3BO3 (boric
acid), and HCl (hydrochloric acid). These materials improve the yield by minimizing the
production of any undesirable byproduct such as TESPM and TESPD.
[0020] In a first embodiment of the process for making the mercaptoalkylalkoxysilanes, a
pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to
provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a
haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture
containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired
mercaptoalklyalkoxysilanes are separated from the water soluble byproducts.
[0021] In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst,
and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen
sulfide, phosphoric acid, boric acid, and hydrochloric acid, and anhydrous salts thereof, are
mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction
mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired
mercaptoalklyalkoxysilanes are separated from water soluble byproducts.
[0022] Following is a list of acronyms used in this application:
CPTES - Chloropropyltriethoxysilane
CPTMS - Chloropropyltrimethoxysilane
MPT AS - Mercaptopropyltrialkoxysilane
MPTES - Mercaptopropyltriethoxysilane
TBAB - Tetrabutylammonium Bromide
TBAC - Tetrabutylammonium Chloride
TESPD - 3,3'bis(triethoxysilylpropyl)disulfide
TESPM - 3,3'bis(triethoxysilylpropyl)monosulfide
[0023] These and other features of the invention will become apparent from a consideration
of the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The synthesis of mercapto-functional alkoxysilanes is carried out via a reaction
using a phase transfer catalysis process in an aqueous/organic medium. The use of small
amounts of gases such as H2S, CO2, and SO2, as well as the use of the other pH adjusting
agents of the invention which are all acidic in nature in the aqueous phase, during the
reaction, minimizes the production of undesirable end products such as TESPM and TESPD.
Therefore, the yield of a mercaptopropyltrialkoxysilane can be significantly increased to more
than 90 percent. As noted, it was also surprisingly discovered that a positive pressure of H2S
or CO2 during the reaction of (i) chloropropyltriethoxysilane with (ii) a sodium hydrosulfide
solution and (iii) tetrabutylammonium bromide catalyst (TBAB) minimized TESPM and
TESPD to less than 1.0 weight percent, compared to about 10 weight percent when no
pressure was maintained.
[0025] In this regard, it is believed that the H2S or CO2 pressure causes a reduction in the
pH of the aqueous phase either by the dissolution of H2S, or there occurs an intermediate
reaction of CO2 with H2O to form carbonic acid. In any event, at a reduced pH, the di-
sodium sulfide impurities are converted to sodium hydrosulfide, and minimize TESPM
formation. Thus, when a sodium hydrosulfide aqueous solution was added to a heated reactor
pressurized with H2S gas and containing TBAB and CPTES, the organic phase after filtration
included more than 90 weight percent of desired end product MPTES, and less than one
weight percent of undesired species TESPM and TESPD.
[0026] Accordingly, the first sequence of steps of the process involves mixing a phase
transfer catalyst with an haloalkylalkoxysilane. Phase transfer catalysts suitable for use
according to the invention are quaternary onium cations. Some representative examples of
quaternary onium salts yielding quaternary ammonium cations that can be used as phase
transfer catalysts are described in US 5,405,985 (April 11, 1995), among which are
tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC),
tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetraphenylarsonium
bromide, and tetraphenylarsonium chloride. The '985 patent is considered as being
incorporated herein by reference. The preferred quaternary onium salts according to this
invention are TBAB and TBAC, most preferably TBAB. These materials are available
commercially from chemical suppliers such as Sigma-Aldrich, Milwaukee, Wisconsin. While
the amount of phase transfer catalyst used in the process can vary, it is preferably used in an
amount of 0.1-10 weight percent, most preferably 0.5-2 weight percent, based on the amount
of haloalkylalkoxysilane being used in the process.
[0027] Haloalkylalkoxysilanes for purposes of this invention are those organosilicon
compounds having a structure generally corresponding to the formula (RO)3_mRmSi-Alk-X,
wherein each R is an independently selected hydrocarbon group containing 1-12 carbon
atoms, such as methyl, ethyl, propyl, butyl, isobutyl, cyclohexyl, or phenyl. Preferably, R is a
methyl or ethyl group, m can be 0, 1, or 2, but preferably m is zero. Alk represents a divalent
hydrocarbon group containing 1-18 carbon atoms, preferably 2-4 carbon atoms, such as
ethylene, propylene, butylene, or isobutylene. Preferably, Alk is a propylene group. X is one
of the halogen atoms, i.e., fluorine, chlorine, bromine, or iodine, preferably chlorine. Some
representative examples of haloalkylalkoxysilanes suitable for use in this invention include
chloropropyltriethoxysilane, chloropropyltrimethoxysilane, chloroethyltriethoxysilane,
chlorobutyltriethoxysilane, chloroisobutylmethyldiethoxy silane,
chloroisobutylmethyldimethoxysilane, and chloropropyldimethylethoxysilane. The
haloalkylalkoxysilane compound most preferred is chloropropyltriethoxysilane.
[0028] The second sequential step of the process is addition of a sulfide compound. The
sulfide compound is a composition having a structure corresponding to the formula M2Sn or
MHS, or mixtures thereof, wherein M represents an alkali metal or ammonium group, and H
is hydrogen. While the alkali metal can be potassium, sodium, rubidium, or cesium, sodium is
preferred. Representative of some preferred compositions of the type MHS include
compositions such as NaHS, KHS, and NH4HS, with NaHS being most preferred. The NaHS
composition can be used in the form of NaHS flakes containing 71.5-74.5 weight percent
NaHS, or an NaHS liquor containing 45-60 weight percent NaHS. Such materials are
available commercially from PPG Industries, Inc., Pittsburgh, Pennsylvania. Optionally,
compositions of the type M2Sn can be used, when it is desired to avoid the necessity of
dissolving solid or flake forms. Suitable compositions of this type include Na2S, K2S, Cs2S,
(NH4)2S, Na2S2, Na2S3, Na2S4, Na2S6, K2S2 K2S3? K2S4, K2S6, and (NH4)2S2. A
particularly preferred sulfide composition is a solution containing 25-72 weight percent of
NaHS, preferably 45-60 weight percent NaHS, also available from PPG Industries, Inc.,
Pittsburgh, Pennsylvania.
[0029] If desired, sulfur (S) can be added as an optional ingredient. A suitable sulfur is
elemental sulfur in the form of an 100 mesh refined sulfur powder available from Sigma-
Aldrich, Milwaukee, Wisconsin. While the amount of sulfur and sulfide compound can vary,
it can be present in a molar ratio corresponding to S/M2Sn or S/MHS of 0 to 2.0, preferably
zero.
[0030] In the preferred embodiment, the phase transfer catalyst and haloalkylalkoxysilane
are combined with a pH adjusting agent which is only slightly acidic in nature or one that is
diluted to such an extent as to be only slightly acidic. The pH adjusting agent can be SO2
(sulfur dioxide), CO2 (carbon dioxide), H2S (hydrogen sulfide), H3PO4 (phosphoric acid),
H3BO3 (boric acid), or HCl (hydrochloric acid). While the amount of pH adjusting agent
added to the aqueous phase can vary, it is generally present in a molar amount of 0.01 to 1.0
mole per mole of M2Sn or MHS being used in the process, preferably 0.01 to 0.3 mole per
mole of M2Sn or MHS being used in the process.
[0031] The process is carried out in an aqueous/organic phase containing the
haloalkylalkoxysilane, phase transfer catalyst, pH adjusting agent, and sulfide compound.
While the amount of water used to create the aqueous phase can vary, it is preferably based
on the amount of haloalkylalkoxysilane being used in the process. The water can be added
directly, or it can be present indirectly, as the water present in small amounts in starting
materials. In any case, the total amount of water for purposes of the invention should include
all water added directly or indirectly. Accordingly, the total amount of water used to create
the aqueous phase is 1-100 weight percent of the amount of haloalkylalkoxysilane being used
in the process, preferably 2.5-70 weight percent, most preferably 20-40 weight percent.
[0032] Although not being willing to be bound by any particular theory, it is believed that
that the addition of only certain pH adjusting agents, i.e., the pH adjusting agents noted
above, to the aqueous phase during the process, controls the pH of the reaction medium so as
to directly affect product formation and minimizes any potential of undesired side reactions.
Thus, the pH is controlled by addition of such pH adjusting agents at rates and concentrations
so as to maintain the pH during the reaction in the range of 4 to 9, preferably in the range of
5-8, and more preferably in the range of 5 to less than 7. The haloalkylalkoxysilane
compound is added to the aqueous phase at such a rate so as to control the exothermic
reaction, and at the same time maintain a temperature in the range of 40-110 °C. Preferably
the reaction temperature is maintained at 60-95 °C. The progress of the reaction can be
monitored by determining the consumption of the haloalkylalkoxysilane. The amount of
catalyst being used as well as the reaction temperature will affect the reaction time necessary
for its completion.
[0033] At the end of the reaction, a product mixture is produced containing an organic
phase, an aqueous phase, and possibly some precipitated solid materials that includes salts
formed during the reaction. The organic phase contains the mercaptoalkylalkoxysilane, and
separation of the mercaptoalkylalkoxysilane from the product mixture can be obtained simply
by phase separation of the organic phase from the aqueous phase, or if precipitated salts are
formed during the reaction, the salts can be separated first by filtering or decanting prior to
the phase separation. Water or a dilute acidic solution can be added to the product mixture
prior to separation, as the addition of water or a dilute acidic solution tends to enhance phase
separation by dissolving precipitated salts.
[0034] The amount of water or dilute acidic solution added during this step can vary from
10-50 weight percent based on the weight of the haloalkylalkoxysilane, preferably 20-40
weight percent, and most preferably 25-35 weight percent. When a dilute acidic solution is
used, it can contain HCl, HNO3, or H2SO4, for example, having normal (N) concentrations
of 0.000001-5, preferably 0.01-1. The dilute acidic solution can also be prepared by adding a
chlorosilane to water, i.e., =Si-Cl + H-OH ? ?Si-OH + HCl.
[0035] Following addition of water or a dilute acidic solution to the product mixture, the
mercaptoalkylalkoxysilane can be isolated from the product mixture by phase separating the
organic phase from the aqueous phase. The organic phase containing the
mercaptoalkylalkoxysilane can also be subjected to a drying step. One example of drying is
to treat the organic phase under vacuum to remove any volatile organic materials present,
along with the residual water. The drying can be to simply heat the organic phase to a
temperature of 20-160 °C under a reduced pressure of 5-35 mm Hg (0.67 to 4.65 kPa),
preferably 90-120 °C at 5-25 mm Hg (0.67 to 3.33 kPa). Alternatively, drying of the organic
phase can be obtained using a thin film stripper to remove volatile organic materials as well
as residual water in the organic phase.
[0036] Yet another drying technique is to contact the organic phase containing the
mercaptoalkylalkoxysilane with a desiccant. The desiccant can be any solid material known
to be capable of removing trace quantities of water from organic phases. Representative
desiccants are typically ionic hygroscopic compositions such as sodium sulfate, magnesium
sulfate, as well as the silicate based compositions such as zeolites, silica, and
alumina/silicates. Preferred desiccants are sodium sulfate or magnesium sulfate, and sodium
sulfate is most preferred.
[0037] The dried organic phase can then be subjected to additional steps to further improve
its final purity and appearance. Thus, the organic phase containing the
mercaptoalkylalkoxysilane can be heated under vacuum to strip low boiling components such
as ethanol, water, tributylamine, and dissolved H2S gas, For example, the organic phase,
when heated to 30-100 °C at 10-200 mm Hg/1.3-27 kPa vacuum, provides a clear product
which has a better shelf life. The organic phase, after stripping the low boiling components
can also be distilled under high vacuum, i.e., 1-20 mm Hg/0.133-2.7 kPa, to provide highly
pure mercaptoalkylalkoxysilanes. As a result, the long-term storage stability of the
mercaptoalkylalkoxysilane is enhanced, i.e., the composition does not change with time or
result in products containing undesirable solid precipitates.
[0038] The following examples are set forth to illustrate the invention in more detail. In
particular, they teach those skilled in the art how to obtain the primary benefits of the present
invention, i.e., increase the yield of MPTES and reduce side product species such as TESPM
and TESPD.
[0039] The purpose of this example is to show no reduction in TESPM formation when
none of the pH adjusting agents of the invention are employed. Thus, in a three neck round
bottom flask equipped with an addition funnel, condenser, stirrer and thermometer, was
added with 100 g (1.26 moles) of NaHS flakes containing 61.7 percent by weight NaHS and
6.07 weight percent Na2S, and 75.62 g of deionized (DI) water. The mixture was heated to 70
°C and mixed to make a bright yellow solution of NaHS. Then, 9.0 g (0.0094 mole)
tetrabutylammonium bromide solution containing 25 weight percent active was added and
mixed. The color of the mixture changed to dark brown, and an oily layer of catalyst
intermediate formed at the interface. Then 317.6 g (1.32 mole) chloropropyltriethoxysilane
was added slowly in 8 minutes while mixing at 500 rpm. The reaction temperature increased
to 82 °C due to an exotherm. The reaction was carried out for 3 hours at 80 °C, and 139.6 g
of deionized water was added after cooling the mixture to 50 °C to dissolve the sodium
chloride salt byproduct. After conducting a phase separation, 287.7 g of an organic phase was
collected. It contained 8.4 weight percent of unreacted CPTES, 61.7 weight percent of
mercaptopropyltriethoxysilane, 9.6 weight percent of TESPM, and 17.82 weight percent of
TESPD, as determined by Gas Chromatograhy (GC) analysis.
[0040] This example is the reverse of Example 1, and shows that the product gelled. Thus,
the order of addition in Example 1 was reversed, and a solution of sodium hydrosulfide flake
was prepared by adding 76.2 g of water to 100.11 g of sodium hydrosulfide flakes. The
solution was added slowly via an addition funnel to a reaction mixture containing 317.6 g of
chloropropyltriethoxysilane and 3.1 g of solid tetrabutylammonium bromide at 67 °C. The
reaction mixture gelled within 5 minutes of the NaHS addition.
[0041] The purpose of this example is to show that while the addition of sulfur reduced the
formation of TESPM, the formation of TESPD increased. Thus, in a similar reaction to the
one in Example 1, the ratio of sulfur to NaHS was increased to 0.05 to convert the TESPM
into TESPD. NaHS flakes (146.3 g., 1.83 mole), sulfur (2.92 g, 0.092 mole), and 100 g DI
water, were mixed in a glass-jacketed reactor and heated to 70 °C. TBAB solution (14.4 g,
0.011 mole) was added and mixed. Instantly, an oily omega phase was formed at the surface.
CPTES (400 g, 1.66 mole) was added at a rate of about 30 ml/min. The reaction temperature
increased to 94 °C due to the exotherm, and some gel was observed in the organic phase.
380.1 g (95 percent by weight of CPTES) organic phase was collected after a three hour
reaction. The gas chromatography analysis showed 1.5 percent CPTES, 66.7 percent MPTES,
3.37 percent TESPM, and 27.9 percent TESPD.
[0042] This example is the same as Example 3 except that a salt was added so that no
gelation would occur in the organic phase. However, while the formation of TESPM was
reduced, the formation of TESPD increased. Accordingly, an excess amount of NaHS flakes
were used, and NaCl salt was added to saturate the aqueous phase before the addition of
CPTES. The sulfur/NaHS ratio was 0.05. The catalyst solution was also added after the
CPTES addition was completed. Thus, NaHS flakes (100 g., 1.248 mole), NaCl 87.7 g, sulfur
(2.0 g, 0.063 mole), and 161.5 g of water, were mixed and heated to 60 °C. CPTES (161.5 g.,
0.671 mole) was added slowly and mixed at 300 rpm. A 25 weight percent solution of TBAB
catalyst was added to the reaction mixture at 65 °C. A slight exotherm was observed, and the
reaction was completed in about 5 hours. The GC analysis of the organic phase showed that it
contained 0.35 weight percent CPTES, 62.2 weight percent MPTES, 1.1 weight percent
TESPM, and 34.1 weight percent TESPD. The product was stable. The MPTES yield was
less due to side reactions when sodium hydrosulfide flakes were used.
[0043] This example shows the benefits obtained by using a solution of NaHS instead of
NaHS flakes. In this example, the yield of MPTES was increased while the amount of the
TESPM and TESPD byproducts decreased, by using the NaHS solution. Thus, NaHS flakes
were replaced with a solution containing 45 weight percent of NaHS. No additional water
was used in the aqueous phase as the NaHS solution contained water. Thus, a solution
containing 45 weight percent NaHS (143 g., 1.15 mole) and 50 weight percent of a TBAB
solution (99.6 g, 0.015 mole) were added into a glass reactor, mixed, and heated to 70 °C.
CPTES (240.8 g., 1.0 mole) was slowly added to maintain the reaction temperature below 80
°C. After 5 hours, the reaction mixture was cooled to room temperature, and water was added
to dissolve the NaCl salt in the aqueous phase. 229 g. of a light yellow organic phase was
collected (95 weight percent based on CPTES), and analyzed. The GC analysis showed that it
contained 1.6 weight percent CPTES, 84 weight percent MPTES, 6.9 weight percent TESPM,
and 1.4 weight percent TESPD. No gel was found in the product. Color in the product was
removed by treating it with 1-2 weight percent activated carbon black and clay.
[0044] The NaHS/CPTES ratio in this example was changed from 1.15 to 1.30. All other
conditions were similar to Example 5. An increase in rate of reaction was observed with an
increase in NaHS concentration in the reaction mixture. No significant change was observed
in the product composition. The reaction was completed in 3 hours. The GC analysis results
showed 0.8 weight percent CPTES, 82.3 weight percent MPTES, 6.6 weight percent TESPM,
and 0.8 weight percent TESPD.
[0045] Example 6 was repeated, except the order of addition of the reactants was reversed.
Thus, CPTES (240.8 g., 1.0 mole) and solid TBAB (4.82 g., 0.015 mole) were added into a
glass reactor, mixed, and heated to 70 °C. A solution containing 45 weight percent NaHS
(160.4 g., 1.30 mole) was added using an addition funnel in about 20 minutes. A slight
exotherm was observed during the initial addition of NaHS. The reaction was stopped after 4
hours, and the byproduct NaCl was dissolved in water. The organic phase recovered after the
phase separation was 225.5 g. (93.6 weight percent based on CPTES). The product
composition by GC analysis showed that it contained 0.83 weight percent CPTES, 84.2
weight percent MPTES, 6.79 weight percent TESPM, and 0.7 weight percent TESPD. There
was a slight improvement in MPTES yield by changing the order of addition of the sodium
hydrosulfide. The GC analysis also showed a lower content of hydrolyzed oligomers than the
GC analysis in Example 6.
[0046] The purpose of this example is to further minimize the TESPM formation and to
increase the MPTES yield. Accordingly, an HCl solution was added dropwise to an NaHS
solution during its reaction with CPTES at atmospheric pressure. Hydrogen sulfide gas
formed in the reaction was neutralized in a caustic scrubber. 150.1 g (1.2 mole) of a 45
percent by weight NaHS solution, and 9.63 g (0.015 mole) of a 50 percent by weight TBAB
catalyst solution, was added to the reactor, mixed, and heated to 65 °C. 100 g (0.15 mole) of a
1.3 molar HCl solution, and 240.0 g (1.0 mole) of CPTES, were added simultaneously from
two addition funnels, at a rate such that the addition of CPTES was completed in 15 minutes,
and the addition of HCl was complete in about an hour. The reaction was continued at 70 °C
for 5 hours. GC data showed 11.4 weight percent of unreacted CPTES remaining, and
therefore 12.48 g (0.1002 mole) of an NaHS solution was again added and reacted for 5
hours. The organic phase was separated after cooling and filtered through a 0.45 micron filter
disc. Gas chromatographic (GC) analysis of the organic phase showed that the product
contained 2.6 weight percent of CPTES, 91.0 weight percent of MPTES, 1.99 weight percent
of TESPM, and 2.34 weight percent of TESPD.
[0047] A 50 percent by weight solution of NaHSC4 was added to an NaHS solution during
its reaction with CPTES. 325 g (2.69 mole) of an NaHS solution, and 8.2 g (0.0124 mole) of
a TBAB solution, were added to a glass reactor, mixed, and heated to 75 °C. The addition
dropwise of NaHSO4 solution was initiated just prior to the addition of CPTES. 497.8 g
(2.07 mole) of CPTES was added to the reaction mixture in 8 minutes. The addition of the
NaHSO4 solution was complete in 30 minutes. The organic phase was separated after a 5
hour reaction and analyzed by GC. The product contained 2.0 percent by weight of CPTES,
87.6 percent by weight of MPTES, 2.7 percent by weight of TESPM, and 0.7 percent by
weight of TESPD. The product was distilled under vacuum to provide a 95.4 percent pure
MPTES at a yield of about 84 percent, based on the amount of CPTES employed.
[0048] Boric acid was used in this example to lower the pH of the reaction mixture. The
order of addition of CPTES and NaHS as compared to Example 10 was also reversed to
minimize any potential formation of a gel. Thus, 206.3 g (0.86 mole) of CPTES, 4.13 g
(0.013 mole) of solid TBAB, and 51.4 g (0.83 mole) of H3BO3, were mixed in ajacketed
glass reactor and heated to 65 °C. 100.0 g (0.83 mole) of an NaHS solution was slowly
added with a dropping funnel over a time interval of 30 minutes. Froth and foaming were
observed due to the reaction of NaHS and boric acid. Additional NaHS solution and TBAB
catalyst were added after reaction with CPTES for 3-4 hours. After a total reaction time of 6
hours, the reaction mixture was cooled, filtered, and phase separated. The product
composition by GC analysis was determined to be 1.2 percent by weight of CPTES, 89.3
percent by weight of MPTES, 2.8 percent by weight of TESPM, and 0.2 percent by weight of
TESPD.
[0049] Sodium di-hydrogen phosphate monohydrate was used as a pH adjusting agent in
this example to reduce the formation of TESPM in the product. Thus, 27.6 g (0.2 mole) of
NaH2PO4.H2O was added to a reactor. 157.4 g (1.30 mole) of a 45 percent by weight
solution of NaHS was slowly added to avoid any violent reaction between NaHS and
dihydrogen phosphate. H2S gas was evolved from the reaction, and was trapped in a caustic
scrubber. 9.63 g (0.015 mole) of a TBAB solution was added, and mixed for 5 minutes. A
very dark green omega phase of a catalyst intermediate formed instantly. The reaction
mixture was slowly heated to 70 °C, and 240.8 g (1.0 mole) of CPTES was added over 15
minutes. The reaction was continued for 4 hours at 70 °C. Upon its cooling and phase
separation, a 227.6 gram organic phase was obtained. The organic phase yield was 94.5
percent, based on the amount of CPTES used in the reaction. GC results of the organic phase
showed 2.8 percent of CPTES, 89.6 percent of MPTES, 4.5 percent of TESPM, and 1.15
percent of TESPD.
[0050] In this example, sodium acetate trihydrate was mixed with an NaHS solution to
reduce the pH of the aqueous phase and to minimize the formation of TESPM. Thus,
equimolar amounts of sodium acetate and NaHS were added to a reactor and mixed. No
change in the pH was observed. The reaction was carried out using a slight molar excess of
CPTES, and in the presence of the TBAB catalyst, as described above in Examples 8-11. GC
results of the final product showed no effect on TESPM reduction, however. The product
contained 83.1 percent by weight of MPTES and 7.38 percent by weight of TESPM.
[0051] In the following examples, a series of experiments were performed using H2S as pH
adjusting agent, at different H2S pressure, to control the pH of reaction mixture and improve
the yield of MPTES.
[0052] A pressure reactor containing NaHS solution was pressurized with H2S gas to 10 psi
at room temperature before reacting it with CPTES in presence of a TBAB catalyst. The H2S
gas in water had a pH of 4.2, and reacted with Na2S byproducts in the aqueous phase to
provide NaHS. It also prevented Na2S formation by maintaining the pH below 9. The
positive pressure of H2S during the reaction also minimized hydrolysis of any alkoxy groups
and polymer formation
[0053] Thus, 139.4 g (1.15 mole) of NaHS solution was added to the reactor and the reactor
was sealed. The reactor was then charged with 10 psi/69 kPa H2S and the contents were
mixed for 5 minutes. A pressure drop was initially observed due to the H2S solubility in
water and its reaction with Na2S. The NaHS was heated to 70 °C, and 9.6 g (0.015 mole) of
a 50 weight percent solution of TBAB and 240.8 g (1.0 mole) of CPTES were fed
consecutively into the reactor using a pressure syringe. The reaction was continued for 3.5
hours at 80 °C before being cooled. Deionized water was added to the reaction mixture to
dissolve any NaCl salt byproduct, and the organic phase was recovered by phase separation.
The GC composition consisted of 1.8 weight percent of CPTES, 87.5 weight percent of
MPTES, 4.6 weight percent of TESPM, and 1.5 weight percent of TESPD. The yield was 90
percent.
[0054] Except for the 50 psi/345 kPa H2S pressure, all other conditions were the same as
Example 13. The reaction was completed in 5 hours. The product composition was 0.4
weight percent of CPTES, 93.0 weight percent of MPTES, 1.9 weight percent of TESPM,
and 0.08 weight percent of TESPD. The product yield was 93.3 percent.
[0055] Except for the 100 psi/690 kPa H2S pressure, all other conditions were the same as
Examples 13 and 14. The product composition after a 5 hour reaction was 0.5 weight percent
of CPTES, 89.8 weight percent of MPTES, 0.8 weight percent of TESPM, and 0.3 weight
percent of TESPD. The yield was 95.3 percent. It can be seen that the yield of MPTES was
improved by suppressing any byproduct formation through control of the pH by the H2S gas.
[0056] This example is the same as Example 14 except that the order of addition of the
reactants is reversed. Also, a solid TBAB catalyst was used to avoid the hydrolysis of
CPTES. Thus, 240.8 g (1.0 mole) of CPTES and 4.8 g (0.015 mole) of solid TBAB catalyst
were loaded into a pressure reactor and the reactor was sealed. The reactor was pressurized
with H2S until the pressure stabilized at 50 psi/345 kPa. The H2S valve was closed, and the
reaction mixture was heated to 70 °C while mixing the contents at 500 rpm. 139.2 g (1.15
mole) of an NaHS solution was then slowly added to the reactor at a rate of about 10 ml/min
using a pressure syringe pump. The reaction temperature increased to 80 °C due to the
exothermic reaction. After 5 hours of reaction at 80°C, the mixture was cooled to 30 °C and
any salt byproducts were dissolved in 69 g of deionized water. Upon cooling and phase
separation, a 229 gram organic phase was obtained. The organic phase yield was 95.4 percent
based on the amount of CPTES used in the reaction. GC results of the organic phase showed
0.9 percent of CPTES, 93.3 percent of MPTES, 0.4 percent of TESPM, and 1.0 percent of
TESPD. Thus, it can be seen that the yield of MPTES was increased when H2S gas was used
in this example of a reverse addition process.
[0057] In the following examples, a series of experiments were performed using CO2 as the
pH adjusting agent, at different CO2 pressure, to control the pH of reaction mixture and
improve the yield of MPTES.
[0058] A pressure reactor containing an NaHS solution was pressurized with CO2 gas to 25
psi/173 kPa at room temperature before reacting it with CPTES in presence of a TBAB
catalyst. The CO2 gas in water was slightly acidic due to the formation of carbonic acid,
which in turn reacts with any Na2S byproduct in the NaHS solution to minimize TESPM
formation, and to improve the overall yield of MPTES. Maintaining a positive pressure of
CO2 during the reaction also minimized any hydrolysis of alkoxy groups and polymer
formation.
[0059] Thus, and similar to Example 12, 139.2 g (1.15 mole) of an NaHS solution was
charged to the pressure reactor and the reactor was sealed. 10 psi/69 kPa CO2 pressure was
applied and the contents were mixed for 5 minutes. The reaction mixture was heated to 70 °C
and 9.6 g (0.015 mole) of aTBAB solution and 240.8 g (1.0 mole) of CPTES were added to
the reactor by a pressure syringe at a controlled rate. The reaction was continued for 5 hours
at 80 °C. The progress of the reaction was monitored by the GC analysis of the organic phase
and the consumption of CPTES. After cooling the reaction mixture and phase separation, the
organic phase was stripped to remove any low boilers and analyzed by GC. The product
contained 0.3 weight percent of CPTES, 92.1 weight percent of MPTES, 2.3 weight percent
of TESPM, and 0.5 weight percent of TESPD. The yield was 91.1 percent based on the
amount of CPTES used.
[0060] Except for CO2 pressure being increased to 50 psi/345 kPa, all other conditions
were the same as Example 16. After phase separation, the organic phase was analyzed by GC,
and it contained 0.5 weight percent of CPTES, 88.8 weight percent of MPTES, 1.3 weight
percent of TESPM, and 2.6 weight percent of TESPD. Similar good results were obtained
when the CO2 was continuously fed to the reactor during a reaction at 50 psi/345 kPa.
[0061] Example 18 was repeated, except that the reaction was performed at 100 psi/690 kPa
CO2 pressure. The pressure increased to 135 psi/932 kPa when the reaction mixture was
heated to 70 °C. The pressure dropped during the CPTES addition as the NaHS was
consumed in the reaction. The organic phase was isolated after completion of the reaction and
analyzed. The product contained 2.3 weight percent of CPTES, 88.2 weight percent of
MPTES, 0.9 weight percent of TESPM, and 2.8 weight percent of TESPD. Color in the
product was removed by treatment with activated carbon black.
[0062] Example 16 was repeated, except that the reaction was carried out under a 50
psi/345 kPa CO2 gas pressure. NaCl and NaHCO3 salts were produced in the reaction. Upon
cooling and phase separation, a 222.8 gram organic phase was obtained. The organic phase
yield was 92.8 percent based on the amount of CPTES used in the reaction. GC results of the
organic phase showed 0.8 percent of CPTES, 92.4 percent of MPTES, 1.2 percent of TESPM,
and 0.5 percent of TESPD.
[0063] The organic phase was also distilled under vacuum, and the product was collected at
68 °C/1 mm Hg/0.133 kPa. After complete distillation, a small amount of solid polymer
residue remained in the pot. The distillate contained 0.9 weight percent of CPTES and 98.0
weight percent of MPTES.
[0064] Other variations may be made in compounds, compositions, and methods described
herein without departing from the essential features of the invention. The embodiments of the
invention specifically illustrated herein are exemplary only and not intended as limitations on
their scope except as defined in the appended claims.
We claim:
1. A process for making mercaptoalkylalkoxysilanes comprising the sequential steps of:
first, mixing (i) a pH adjusting agent and (ii) a sulfide containing compound of the
formula M2Sn or MHS where M is an alkali metal or an ammonium group and H is
hydrogen, in an aqueous phase, to provide a pH in the range of 4-9 of the aqueous phase,
second, adding (iii) a phase transfer catalyst to the aqueous phase,
third, adding (iv) a haloalkylalkoxysilane to the aqueous phase, to form a reaction
mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and
Fourth, separating the desired mercaptoalkylalkoxysilanes from the water soluble
byproducts.
2. The process according to Claim 1 in which the pH adjusting agent is sulfur dioxide,
carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, or hydrochloric acid.
3. The process according to Claim 2 in which the pH adjusting agent is carbon dioxide or
hydrogen sulfide.
4. The process according to Claim 3 in which the pressure of the carbon dioxide or hydrogen
sulfide is 10-200 psi/69-1,380 kPa.
5. The process according to Claim 4 in which the pressure is 25-100 psi/173-690 kPa.
6. The process according to Claim 1 in which the pH in the aqueous phase is 5-8.
7. The process according to Claim 6 in which the pH in the aqueous phase is 5 to less than 7.
8. The process according to Claim 1 in which the reaction temperature is 40-110 °C.
9. The process according to Claim 8 in which the reaction temperature is 60-95 °C.
10. The process according to Claim 1 in which the haloalkylalkoxysilane has the formula
(RO)3-mRmSi-Alk-X wherein each R is a hydrocarbon group containing 1-12 garbon atoms;
m is 0, 1, or 2; Alk represents a divalent hydrocarbon group containing 1-18 carbon atoms;
and X is chlorine, bromine, or iodine.
11. The process according to Claim 10 in which the haloalkylalkoxysilane is
chloropropyltriethoxysilane, chloropropyltrimethoxy silane, chloroethyltriethoxysilane,
chlorobutyltriethoxy silane, chloroisobutylmethyldiethoxysilane,
chloroisobutylmethyldimethoxy silane, or chloropropyldimethylethoxysilane.
12. The process according to Claim 11 in which the haloalkylalkoxysilane is
chloropropyltriethoxysilane.
13. The process according to Claim 1 in which the sulfide-containing compound is sodium
hydrosulfide, potassium hydrosulfide, or ammonium hydrosulfide, disodium sulfide,
dipotassium sulfide or diammonium sulfide.
14. The process according to Claim 13 in which the sulfide-containing compound is sodium
hydrosulfide.
15. The process according to Claim 14 in which the sodium hydrosulfide is an aqueous
solution containing 25-72 percent of sodium hydrosulfide.
16. The process according to Claim 15 in which the aqueous solution contains 40-50 percent
of sodium hydrosulfide.
17. The process according to Claim 1 in which the phase transfer catalyst is a quaternary
onium salt.
18. The process according to Claim 17 in which the phase transfer catalyst is
tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylphosphonium
bromide, tetrabutylphosphonium chloride, tetraphenylarsonium bromide, or
tetraphenylarsonium chloride.
19. The process according to Claim 18 in which the phase transfer catalyst is
tetrabutylammonium bromide.
20. The process according to Claim 1 in which the aqueous phase is saturated with sodium
chloride.
21. The process according to Claim 1 in which the aqueous phase in the first step of the
process is free of sodium chloride.
22. A process for making mercaptoalkylalkoxysilanes comprising the sequential steps of:
first, mixing together (i) a haloalkylalkoxysilane, (ii) a phase transfer catalyst, and
(iii) an anhydrous pH adjusting agent,
second, adding an aqueous solution of a sulfide containing compound or mixture of
compounds of the formula M2Sn or MHS where M represents an alkali metal or ammonium
group and H represents hydrogen, to form an aqueous reaction mixture with a pH in the range
of 4-9 containing mercaptoalkylalkoxysilanes and water soluble byproducts, and
third, separating the desired mercaptoalklyalkoxysilanes from the water soluble
byproducts.
23. The process according to Claim 22 in which the pH adjusting agent is sulfur dioxide,
carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, or hydrochloric acid.
24. The process according to Claim 23 in which the pH adjusting agent is carbon dioxide or
hydrogen sulfide.
25. The process according to Claim 24 in which the pressure of the carbon dioxide or
hydrogen sulfide is 10-200 psi/69-1,380 kPa.
26. The process according to Claim 25 in which the pressure is 25-100 psi/173-690 kPa.
27. The process according to Claim 22 in which the pH is 5-8.
28. The process according to Claim 27 in which the pH is 5 to less than 7.
29. The process according to Claim 22 in which the reaction temperature is 40-110 °C.
30. The process according to Claim 29 in which the reaction temperature is 60-95 °C.
31. The process according to Claim 22 in which the haloalkylalkoxysilane has the formula
(RO)3-mRmSi-Alk-X wherein each R is a hydrocarbon group containing 1-12 carbon atoms;
m is 0, 1, or 2; Alk represents a divalent hydrocarbon group containing 1-18 carbon atoms;
and X is chlorine, bromine, or iodine.
32. The process according to Claim 31 in which the haloalkylalkoxysilane is
chloropropyltriethoxysilane, chloropropyltrimethoxy silane, chloroethyltriethoxysilane,
chlorobutyltriethoxy silane, chloroisobutylmethyldiethoxysilane,
chloroisobutylmethyldimethoxy silane, or chloropropyldimethylethoxysilane.
33. The process according to Claim 32 in which the haloalkylalkoxysilane is
chloropropyltriethoxysilane.
34. The process according to Claim 22 in which the sulfide-containing compound is sodium
hydrosulfide, potassium hydrosulfide, or ammonium hydrosulfide, disodium sulfide,
dipotassium sulfide or diammonium sulfide.
35. The process according to Claim 34 in which the sulfide-containing compound is sodium
hydrosulfide.
36. The process according to Claim 35 in which the aqueous solution contains 25-72 percent
of sodium hydrosulfide.
37. The process according to Claim 36 in which the aqueous solution contains 40-50 percent
of sodium hydrosulfide.
38. The process according to Claim 22 in which the phase transfer catalyst is a quaternary
onium salt.
39. The process according to Claim 38 in which the phase transfer catalyst is
tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylphosphonium
bromide, tetrabutylphosphonium chloride, tetraphenylarsonium bromide, or
tetraphenylarsonium chloride.
40. The process according to Claim 39 in which the phase transfer catalyst is
tetrabutylammonium bromide.
41. The process according to Claim 22 in which the aqueous reaction mixture is saturated
with sodium chloride.
42. The process according to Claim 22 in which the mixture in the first step of the process is
free of sodium chloride.
In a first embodiment of a process for making mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing
compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase,
a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and
water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. In an alternate
embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide,
carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, are mixed, then an aqueous solution of a sulfide
containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and
desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts.

Documents:

1979-KOLNP-2004-FORM-27.pdf

1979-kolnp-2004-granted-abstract.pdf

1979-kolnp-2004-granted-assignment.pdf

1979-kolnp-2004-granted-claims.pdf

1979-kolnp-2004-granted-correspondence.pdf

1979-kolnp-2004-granted-description (complete).pdf

1979-kolnp-2004-granted-examination report.pdf

1979-kolnp-2004-granted-form 1.pdf

1979-kolnp-2004-granted-form 18.pdf

1979-kolnp-2004-granted-form 3.pdf

1979-kolnp-2004-granted-form 5.pdf

1979-kolnp-2004-granted-gpa.pdf

1979-kolnp-2004-granted-reply to examination report.pdf

1979-kolnp-2004-granted-specification.pdf

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Patent Number

233929

Indian Patent Application Number

1979/KOLNP/2004

PG Journal Number

17/2009

Publication Date

24-Apr-2009

Grant Date

22-Apr-2009

Date of Filing

22-Dec-2004

Name of Patentee

DOW CORNING CORPORATION

Applicant Address

2200 WEST SALZBURG ROAD, MIDLAND, MI

Inventors:

#	Inventor's Name	Inventor's Address
1	BOSWELL LISA MARIE	4808 BRIARWOOD COURT, AUBURN, MI 48611
2	MAKI WILLIAM CHARLES	811 STILL MEADOW LANE, MIDLAND, MI 48642
3	TOMAR ANIL KUMAR	2200 NORTH YASIMIN COURT, MIDLAND, MI 48642

PCT International Classification Number

C07F 7/18

PCT International Application Number

PCT/US2003/025101

PCT International Filing date

2003-08-11

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10/219,080	2002-08-16	U.S.A.