Title of Invention

PROCESS FOR MAKING GLYPHOSATE

Abstract

A process tor preparing giyphosate of the formula (1): wherein R'. R4. and RS Ire independently hydrogen. substituted or unsubstituted hydrOCBfbyl. or an agronomicllly looeptlble cation, the process comprising contacting a solution contliBinB In N -substituted giyphosate with 8 noble met.1 qatalyst such 8S herein describ8~ and introducing oxygen into the solution, wherein the N -substituted giypho88te has tho formula (ll): R 'and R2 are indopendently hydrogen. blJo8on. -PO,ll3, -SO~2.-N02, or substituted or unsubstituted hydroClrhyJ other thin -CO~; and R3. R4,and R5afe IS previously defined.

Full Text

This invention generally relates to a procesa for converting N-substituted N-(phosphonomethyl)glycines (sometimes referred to as "N-substitUted glyphosate"), as well as esters and salts thereof, to N-(phosphononiethyl) glycine (sometimes referred to as "glyphosate"), as well as esters and salts thereof, via a noble-metal catalyzed oxidation reaction. This invention is particularly directed to converting N-substituted glyphoaateg, as well as esters and salts thereof, having a single N-carboxymethyl functionality. Glyphosate is described by Franz in U.S. Patent No. 3,799,758 and has the following formula: II Glyphosate and its salts conveniently are applied as a post-emergent herbicide in an aqueous formulation. It is a highly effective and commercially important broad-spectrum herbicide useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. Various methods for making glyphosate from N-substituted glyphosates are known in the art. For example, in U.S. Patent No. 3,956,370, Parry et al. teach that N-benzylglycine may be phosphonomethylated to N-benzyl glyphosate, and then reacted with hydrobromic or hydroiodic acid to cleave the benzyl group and thereby produce glyphosate. In U.S. Patent No. 3,927,080, Gaertner teaches that N-t-butylglycine may be phosphonomethylated to form N-t-butyl glyphosate, and then converted to glyphosate via acid hydrolysis, Glyphosate also may be produced from N-benzyl glyphosate via hydrogenolysis, as described, for example, in European Patent Application No. 55,695 and Maier, L. Phosphorus. Sulfur and Silicon. 61, 65-7 (1991). These processes are problematic in that they produce undesirable byproducts such as isobutylene and toluene which create difficulties due to their potential toxicities. Moreover, acid hydrolysis and hydrogenation of N-substituted glyphosates has been demonstrated only for alkyl groups such as tertiary butyl and benzyl groups which are known to be susceptible to such reactions. Dealkylation of N-methyl, N-isopropyl, and other N-substituted glyphosates which are not readily susceptible to acid hydrolysis or catalytic hydrogenation has not been demonstrated. Other methods for making glyphosate are directed to oxidatively cleaving N-(phosphonomethyl)iminodiacetic acid (sometimes referred to as "PMIDA"): > PMIDA may be synthesized from phosphorus trichloride, formaldehyde, and an aqueous solution of the disodium salt of iminodiacetic acid, as described by Gentilcore in U.S. Patent No. 4,775,498: \|,, . ;.. , . jtt 0 ^ line I D ■ H^pCij ■ ;^ii.3L ir ' F^ M I n .It is well-known in the art that PMIDA may be converted into glyphosate by heterogeneous oxidation over carbon catalysts as described, for example, in U.S. Patent No. 3,950,402 to Franz and U.S. Patent No. 4,654,429 to Balthazor et al.; by homogenous catalytic oxidation as described, for example, in Riley et al. J. Amer. Chem. Soc. 113, 3371-78 (1991) and Riley et al. Inorg. Chem. 30, 4191-97 (1991}; and by electrochemical oxidation using carbon electrodes as described, for example, in U.S. Patent No. 3,835,000 to Frazier et al. These oxidation methods, however, have been reported to be useful only for preparing glyphosate from PMIDA, an N-substituted glyphosate having two N-carboxymethyl functionalities. None of these prior art oxidation methods have been reported to be useful for preparing glyphosate from N-substituted glyphosate compounds having only one N-carboxymethyl functionality, i.e., where R' in the following formula is other than -CH^COjH: D II nH ■OH ?. iin—1:_( II,-—N—i.H —p I To the contrary, many prior art references suggest that if R' is a functionality other than a -CHjCO^H group, the prior art methods will cleave the -CHjCOjH group rather than R', and will therefore fail to produce glyphosate. This is particularly true for the prior art which is directed to heterogenous catalytic oxidations over carbon and electrochemical oxidations using carbon electrodes. The mechanisms for these oxidations are well known in the art, particularly for electrochemical oxidations where it is known as the Kolbe reaction, described in various organic electrochemistry books, e.g., S. Torii and H. Tanaka, Organic Electrochemistry 535-80 (H. Lund and M.M. Baizer eds., Marcel Dekker, 3rd ed. 1991). Both mechanisms involve the oxidative degradation of carboxylic acid to a carbon radical and carbon dioxide: There is no suggeation that these mechaniams could be used to cleave any other functionality besides -CHjCOjH, Thus, a more general method for oxidizing N-substituted glyphosates to glyphosates is therefore desirable. Such a method would allow a wider range of N-substituted glycines to be used as raw materials for the production of glyphosate. Such a method also could be used to make glyphosate from N-methylglyphosate (sometimes referred to as "NMG"), an undesirable byproduct from the carbon-catalyzed oxidation of PMIDA. SUMMARY OF THE IHVEHTIOH Among the objects of the invention, therefore, is to provide a process for making glyphosate {as well as its salts and eaters} by oxidizing K-Bubstituted glyphosates (as well as salts and eaters thereof). More particularly, it is an object of this invention to provide a process for making glyphosate (as well as its salts and esters) by oxidizing N-substituted glyphosates.(as well as salts and esters thereof) having a single N-carboxymethyl functionality. For example, it is an object of this invention to provide a process for making glyphosate by oxidizing KMG. Briefly, therefore, the present invention is directed to a novel process for making a composition having the formula (I): (I) In this formula, R^ R\ and R^ are independently hydrogen, substituted or unsubstituted hydrocarbyl, or an agronomically acceptable cation. This invention comprises contacting a solution with a noble metal catalyst and introducing oxygen into the solution. The solution contains an N-substituted glyphosate having the formula (II) : (II) In formula (II}, R^ and R^ are independently hydrogen, halogen, -PO3H2, -SO3H: , -NO2, or substituted or unsubstituted hydrocarbyl other than -CO^H. R^, R*, and R^ are as defined above for formula (I) above. In another embodiment of this invention, the composition (i.e., formula (I)) to be prepared is glyphosate or a salt thereof, and the N-substituted glyphosate (i.e., formula (II)) is NMG or a salt thereof. During the process, a solution having a temperature of from about 125 to about 150°C and containing NMG or a salt thereof is contacted with a noble metal catalyst comprising platinum. Also during the process, 2,2,6,6-tetramethyl piperidine N-oxide is added to the solution. Further, oxygen is introduced into the solution at a rate which imparts a finite dissolved oxygen concentration in the solution that is no greater than 2.0 ppm. A third embodiment of this invention is directed to a noble metal oxidation catalyst having a hydrophobic electroactive molecular species adsorbed on it. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 ahowa the chemical steps that may be taken to produce glyphoaate in accordance with this invention using various N-eubstituted glycine precursors. Figure 2 summarizes various compounds that may be produced during the oxidation of NMG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a novel and useful method for manufacturing glyphoaate, its salts, and its estera, in an aqueous medium wherein an N-substituted glyphoaate or a salt or ester thereof {collectively referred to as "N-substituted glyphoaate reactant") is oxidatively cleaved with oxygen over a noble metal catalyst. Advantages of preparing glyphosate from N-eubstituted glyphosates using this method include the simplicity of the procedure, the low cost of the oxidant (e.g., air or molecular oxygen), and the durability of the catalyst (i.e., little or no deactivation of the catalyst over several cycles). Unlike the prior art methods for oxidatively cleaving N-subatituted glyphosates to make glyphosate, this method is not limited to the oxidation of PMIDA {which has two N-carboxymethyl functionalities). Instead, this method also may be used to make glyphosate by oxidatively cleaving N-substituted glyphosates having only one N-carboxymethyl functionality. This invention, therefore, significantly widens the range of N-substituted glyphosates that may be oxidized to make glyphosate. This, in turn, significantly widens the range of N-substituted glycines (a precursor to many N-substituted glyphosates) which may serve as the raw material to prepare glyphoaate. This invention also is valuable because it provides a method to prepare glyphosate from NMG, an undesirable byproduct from the carbon-catalyzed oxidation of PMIDA. wherein preferably R1 and R2 are independently hydrogen, halogen, -PO3H2, -SO2H , -NO2, or a substituted or unsubstituted hydrocarbyl other than -CO2H; and R3 R4 and R^ are independently hydrogen, a substituted or unsubstituted hydrocarbyl, or an agrononically acceptable cation. As used herein, the term "hydrocarbyl" is defined as a radical consisting exclusively of carbon and hydrogen. The hydrocarbyl may be branched or unbranched, may be saturated or unsaturated, and may contain one or more rings. Suitable hydrocarbyl moieties include alkyl, alkenyl, alJcynyl, and aryl moieties. They also include alkyl, alkenyl, alkynyl, and aryl moieties substituted with other aliphatic or cyclic hydrocarbyl groups, such as alkaryl, alkenaryl and alkynaryl. The term "substituted hydrocarbyl" is defined as a hydrocarbyl wherein at least one hydrogen atom has been substituted with an atom other than hydrogen. For example, the hydrogen atom may be replaced by a halogen atom, such as a chlorine or fluorine atom. The hydrogen atom alternatively may be substituted by an oxygen atom to form, for example, a hydroxy group, an ether, an ester, an anhydride, an aldehyde, a ketone, or a carboxylic acid (except that neither R^ nor R^ may be a carboxy group, i.e., -COjH) . The hydrogen atom also may be replaced by a nitrogen atom to form an amide or a nitro functionality, although substitution by nitrogen to form an amine or a nitrile functionality preferably should be avoided. In additic^^Jihe hydrogen atom may be replaced with a sulfur atom to form, for example, -SO3H , although substitution by sulfur to form a thiol ahould be avoided. It should be recognized that R^ and R^ may together form a ring. This ring may be either a hydrocarbon ring or a heterocycle, and at least one hydrogen on the ring may be substituted as described above for substituted hydrocarbyl functionalities. In a preferred embodiment, R^, R\ R*, and R^ are each hydrogen, and R^ is a linear, branched, or cyclic hydrocarbyl containing up to about 19 carbon atoms. In a more preferred embodiment, R\ R\ and R^ are each hydrogen, and -CHR^R^ is methyl (i.e., R^ and R^ are hydrogen), isopropyl (i.e., R^ and R= are -CH^} , benzyl (i.e., R^ is hydrogen and R^ is phenyl), or n-pentyl (i.e., R^ is hydrogen and R^ is a 4-carbon, straight-chain hydrocarbyl). Many N-substituted glyphosate reactants may be prepared by phosphonomethylating the corresponding N-substituted glycines, their salts, or their amides, for example, by the following reaction: Phosphonomethylation of secondary amines is well-known in the art, and discussed at length in Redmore, D. Topics in Phosphorous Chemistry. Vol. 8, 515-85 (E.G. Griffith & M, Grayson eds., John Wiley & Sons 1976); and in a chapter entitled "a-substituted Phosphonates" in Mastalerz, P. Handbook of Organophosphorus Chemistry 277-375 (Robert Engel ed.. Marcel Dekker 1992). Several methods may be used to prepare N-substituted glycines and their salts and amides. In one embodiment of this invention, the N-substituted glycine is prepared by the condensation of hydrogen cyanide, This reaction is described by Franczyk in U.S. Patent Nos. 5,292,936 and 5,367,112, and by Ebner et al. in U.S. Patent No. 5,627,125. The N-eubstituted ethanolamine precursor may be prepared in at least two waya. First, ketones may be condensed with monoethanolamine in the presence of hydrogen, a solvent, and a noble metal catalyst. This reaction is described in Cope, A.C. and Hancock, E.M. J. Am. Chem. Soc., 64, 1503-6 {1942). N-aubstituted ethanolamines also may be prepared by reacting a mono-substituted amine (such as methylamine) with ethylene oxide to form the mono-substituted ethanolamine. This reaction is described by Y. Yoshida in Japanese Patent Application No. 95-141575. The resulting N-substituted glycine salt may be converted to N-subatituted glyphosate by reacting it with phosphorus trichloride (PClj) in water, and then filtering out the salt and adding formaldehyde. In an alternative embodiment of this invention, N-substiCuted glycine is prepared by condensation of N-substituted amides, formaldehyde, and carbon monoxide in This reaction (i.e., carboxymethylation) is described by Seller et al. in European Patent Application No. 0680948; and Knifton, J.F. Applied Homogeneoua Catalysis 159-68 (B. Cornils et al. eds., VCH, Weinheim, Germany 1996). The product of this reaction is the N-acetyl of the N-subatituted glycine which may be hydrolyzed to the N-substituted glycine. The N-substituted glycine then may be converted into the corresponding N-substituted glyphosate by reacting it with phosphorous acid and formaldehyde in the presence of a strong acid, and then removing the carboxylic acid by methods generally known in the art, such as distillation or membrane separation. In a further embodiment of this invention, the N-substituted glycine is prepared by the reductive alkylation of glycine achieved by reacting carbonyl compounds with glycine and hydrogen in the presence of a catalyst: This reaction is described by Sartori et al. in U.S. Patent No. 4,525,294. The N-substituted glycine may be WE CLAIM: 1. A process for preparing glyphosate of the formula (I): wherein R3, R4, and R5 are independently hydrogen, substituted or unsubstituted hydrocarbyl, or an agronomically acceptable cation, the process comprising contacting a solution containing an N-substituted glyphosate with a noble metal catalyst comprising a metal selected from palladium, platinum, rhodium, iridium. osmium and gold, and introducing oxygen into the solution, wherein the N-substituted glyphosate has the formula (II): R1and R2 are independently hydrogen, halogen, -PO3H1, -SOSHIJ-NOI, or substituted or unsubstituted hydrocarbyl other than - CO2H; and R3, R4,and R^ are as previously defined. 2. The process as claimed in claim 1, wherein R3, R4, and R55 are independently hydrogen or an agronomically acceptable cation. 3. The process as claimed in claim 2 ,wherein R1 is hydrogen and R2 is - PO3H2. 4. The process as claimed in claim 2, wherein R1 is hydrogen and R2 is a linear, branched, or cyclic hydrocarbyl containing up to about 19 carbon atoms. 5. The process as claimed in claim 2 , wherein R1 and R2 are hydrogen. 6. The process as claimed in claim 5, wherein the noble metal catalyst is on a support surface, the support comprising graphitic carbon. 7. The process as claimed in claim 5, wherein the noble metal catalyst has a hydrophobic electroactive molecular species absorbed thereon. 8. The process as claimed in claim 7, wherein the electroactive molecular species has an oxidation potential of at least about 0.3 volts vs. SCE. 9.The process as claimed in claim 7 wherein the electroactive molecular species is tri-phenylmethane; N-hydroxyphthalimide;2,4,7 trichlorofluorene ; tris (4-bTomophenyl)amine; 2, 2, 6, 6tetramethyi piperidine N-oxide; 5, 10, 15, 20 -tetraphenyl -21H, 23H - porphine iron (HI) chloride; 5, 10, 15, 20 - tetraphenyl -21 H, 23 H porphine nickle (II); 4,4'- difluorobenzophenone ; 5, 10,15, 20 - tetrakis (pentafluorophenyl) - 21H, 23H - porphine iron (III) chloride; or phenothiazine. 10. The process as claimed in claim 7 , wherein the electroactive molecular species is N-hydroxyphthalimide; tris (4-bromophenyl) amine; 2, 2, 6, 6 - tetramethyl piperidine N-oxide; 5,10, 15, 20 tetraphenyl- 21H, 23H - porphine iron (Ill)chloride; 5, 10, 15, 20 - tetraphenyl- 21H, 23H porphine nickle (II); or phenothiazine. 11. The process as claimed in claim 7, wherein the electroactive molecular species is N-hydroxyphthalimide; 2, 2, 6, 6 - tetramethyl piperidine N-oxide; 5,10, 15, 20 - tetraphenyl - 21H, 23H - porphine iron (III) chloride; or 5,10,15, 20 - tetraphenyl - 21H, 23H porphine nickle (II). 12. The process as claimed in claim 7 , wherein the electroactive molecular species is 2,1,6,6- tetramethyl piperidine N-oxide. 13. The process as calimed in claim 7 , wherein the electroactive molecular species is phenothiazine. 14. The process as claimed in claim 7 , wherein the noble metal catalyst comprises platinum. 15. The process as claimed in claim 5 ,wherein the solution optionally contains a phosphonomethylated species in addition to the N-substituted glyphosate. 16. The process as claimed in claim 5, wherein the solution optionally contains glyphosate, aminomethylphosphonic acid, N-methyl-aminomethylphosphonic acid, or phosphoric acid. , 17. The process as claimed in claim 2 , wherein R' and R'^ are -CH3. 18. The process as claimed in claim 17 ,wherein (a) the noble metal catalyst is on a support surface, the support comprising graphitic carbon; and (b) the noble metal catalyst has a hydrophobic eiectroactive molecular species absorbed thereon. 19. The process as claimed in claim 18, wherein the eiectroactive molecular species is triphenylmethane; N-hydroxyphthalimide; 2,4,7-trichlorofluorene; tris (4-bromophenyI) amine; 2, 2, 6, 6-tetramethyl piperidine N-oxide; 5,l0,15,20-tetraphenyl-21H,23H -porphine iron (III) chloride; 5,10,15,20-tetraphenyl- 21H, 23H porphine nickle(n); 4,4'- difluorobenzophenone; 5,10,15, 20 tetrakis(pentafluorophenyl)-21H, 23H-porphine iron (III) chloride; or phenothiazine. 20. The process as claimed in claim 18, wherein the eiectroactive molecular species is triphenylmethane or N- hydroxyphthalimide. 21. The process as claimed in claim 2 ,wherein R' is hydrogen and R^ is a straight - chain hydrocarbyl containing 4 carbon atoms. 22. The process as claimed in claim 2, wherein R' is hydrogen and R is phenyl. 23. The process as claimed in claim 1 wherein the noble metal catalyst comprises platinum. ^. ■ The process as claimed in claim 1, wherein the noble metal catalyst is on a support surface, the support comprising carbon, alumina, silica, titania, zirconia, siloxane, or barium sulfate. 25. The process as claimed in claim 24 .wherein the support comprises silica, titania, and barium sulfate. ^. The process as claimed in claim 1, wherein the oxygen is fed at a rate which imparts a finite dissolved oxygen concentration in the solution that is no greater than 2.0 ppm. 27. The process as claimed in claim 1, wherein the weight ratio of the noble metal catalyst to the N-substituted glyphosate is from l:500to 1:5. 2^. The process as claimed in claim 27, wherein the weight ratio of the noble metal catalyst to the N-substituted glyphosate is from 1:200 to 1:10. ^. The process as claimed in claim T7j wherein weight ratio of the noble metal catalyst to the N-substituted glyphosate is from 1:50 to 1:10. 3^ The process as claimed in claim 1, wherein the process is operated at a temperature of from 50 to 200^. _3J_- The process as claimed in claim ^, wherein the process is operated at as tremperature of from 70 to 150'*C. '32. The process as claimed in claim 30wherein the process is operated at a temperature of from 125 to 150°C. 33. The process as claimed in claim 30,wherein the process is operated at a temperature of from 125 to 150*'C and at a pressure of from 40 psig to 100 psig. 34, The process as claimed in claim 1, wherein the process is operated under a gaseous environment having an oxygen partial pressure of from 0.5 to 10 atm. 3^. The process as claimed in claim 1, wherein 2,2,6,6 - tetramethyl piperidine N-oxide is optionally added to the solution. 36. The process as claimed in claim 1, wherein a sub-stoichiometric amount of base is optionally added to the solution. _37. A process for preparing glyphosate substantially as herein above described with reference to the accompanying drawings.

Documents:

536-mas-1999 abstract.pdf

536-mas-1999 claims.pdf

536-mas-1999 correspondence others.pdf

536-mas-1999 correspondence po.pdf

536-mas-1999 description (complete).pdf

536-mas-1999 form-1.pdf