Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF HIGH SELECTIVE DIPHENYL OXALATE"

Abstract

An improved process for the preparation of high selective diphenyl oxalate The present invention relates to an improved process for the preparation of high selective diphenyl oxalate. In particular, the present invention relates to a high selectivity process for the preparation of diphenyl oxalate by transesterification of diethyl oxalate with phenol. The high selectivity process for preparing diphenyl oxalate by transesterification of diethyl oxalate with phenol uses silica supported molybdenum oxide (MoO3/SiO2) solid acid catalyst prepared by sol-gel technique. By the process of present invention diphenyl oxalate is prepared selectively from diethyl oxalate in high yields without any formation of ethyl phenyl oxalate. The present process is an efficient and environmentally benign catalytic process for selective synthesis of diphenyl oxalate.

Full Text

The present invention relates to an improved process for the preparation of high selective diphenyl oxalate. In particular, the present invention relates to a high selectivity process for the preparation of diphenyl oxalate by transesterification of diethyl oxalate with phenol. Still more specifically, the invention relates to a high selectivity process for preparing diphenyl oxalate by transesterification of diethyl oxalate with phenol using silica supported molybdenum oxide (MoO3/SiO2) solid acid catalyst prepared by sol-gel technique. By the process of present invention diphenyl oxalate is prepared selectively from diethyl oxalate in high yields without any formation of ethyl phenyl oxalate. The present process is an efficient and environmentally benign catalytic process for selective synthesis of diphenyl oxalate. Polycarbonates are excellent engineering thermoplastic with good mechanical and optical properties as well as electrical and heat resistance properties useful for many applications. Aromatic carbonates mainly diphenyl carbonate (DPC) is precursor for the production of aromatic polycarbonate by melt polymerization process which is presently very important process in the polycarbonate industry. The present commercial process for polycarbonate synthesis involves interfacial polycondensation of bisphenol-A with phosgene and thus has major disadvantage of high toxicity and corrosion due to phosgene. It also involves complex work up procedure for removal of ionic material and use of large volume of water soluble toxic methylenechloride, which is ten times the weight of the product (Encyclopedia of Polymer Science and engineering Vol. 11, 1987, page 649). Hence it is highly desired to develop an alternate process for the preparation of diphenyl oxalate. One of the non phosgene routes for preparation of polycarbonate is the synthesis of DPC followed by transesterification with bisphenol-A. DPC is also prepared by decarbonylation of diphenyl oxalate, which is obtained by transesterification of dimethyl oxalate with phenol (Pure Applied Chemistry 68, 367, 1996). The US patents 5834615, 5922827 and 5811573 teach the preparation of diphenyl oxalate by transesterification of dimethyl oxalate and phenol in liquid phase using traditional Lewis acid catalysts and soluble Pb, Sn, or Ti organic compounds. Apart from the well known drawbacks of difficulties in product and catalyst separation of homogeneous catalytic systems, the conversion and selectivities are also very low. The references may also be made to EP patent 832872 wherein the synthesis of DPC is described by reacting carbon monoxide with an alkyl nitrite and alkyl alcohol to form dialkyl oxalate which is further reacted with hydroxyaryl compounds to obtain diaryl oxalate. The diaryl oxalate is decarbonylated to produce DPC. The reference may be made to EP patents 1081174 and 0795539 wherein a process for the preparation of DPC is described, which involves the transesterification of dialkyl oxalate with phenol followed by decarbonylation. The reference may be made to the WO patent 2000052077 wherein the manufacture of polycarbonate resin is described by transesterification of dialkyl oxalate and phenolic compound to obtain the diaryl oxalate, which is further decarbonylated to obtain a diaryl carbonate. The diaryl carbonate obtained is further reacted with polyhydroxy compound to obtain polycarbonate. The reference may be made to JP patent 10158216 wherein the preparation of diaryl oxalates and alkyl aryl oxalates is described by continuously feeding dialkyl oxalates, aromatic hydroxy compounds, and catalysts in their liquid states to the 1st reaction zone of a reactor having multiple reaction zones and obtaining a reaction mixture containing the resulting aryl oxalates from the last reaction zone, vapors containing aliphatic alcohols as byproducts are continuously extracted from the upper part of the reactor and the heavy components are cycled into the 1st reaction zone. Different solid acid catalysts have been used for synthesis of diphenyl oxalate by transesterification of dialkyl oxalate and phenol. (Catal. Comrnun. 5, 179 (2004), Catal. Comrnun. 5, 101 (2004), J. Mol. Catal. A 207, 213 (2004). J. Mol. Catal. A 214, 273 (2004)). In all the above processes dimethyl oxalate is used as precursor for synthesis of diphenyl oxalate, and the major product formed is methyl phenyl oxalate and anisole in some cases. The methyl phenyl oxalate formed is further disproportionated to diphenyl oxalate in all the cases. The moderate to low conversions and poor selectivity for diphenyl oxalate are the major disadvantages of the above processes. In all the above processes diphenyl oxalate is prepared in two steps, dimethyl oxalate to methyl phenyl oxalate and disproportionation of methyl phenyl oxalate to diphenyl oxalate The main object of the present invention is to provide a high selectivity process for the preparation of diphenyl oxalate, which obviates the drawbacks as detailed above. Another object of the present invention is to develop a high selectivity process for preparation of diphenyl oxalate by transesterification of diethyl oxalate with phenol. Still another object of the present invention is to develop a high selectivity process using silica supported molybdenum oxide (MoO3/SiO2) solid acid catalyst prepared by sol-gel technique. Yet another object of the present invention is to enhance the catalyst activity and selectivity for diphenyl oxalate. Accordingly the present invention provides an improved process for the preparation of high selective diphenyl oxalate, which comprises reacting diethyl oxalate with phenol in the presence of MoO3/SiO2 solid acid catalyst, in an inert atmosphere, at a temperature in the range of 160 to 250 °C, for a period of at least 5 hrs to obtain the resultant mixture containing diphenyl oxalate, distilling the above said resultant reaction mixture successively in fraction to obtain the enriched diphenyl oxalate in high yield. In an embodiment of the present invention the MoO3/SiO2 catalyst used has MoO3 to SiO2 ratio in the range of 1:99 to 20:80. In yet another embodiment the mole ratio of diethyl to phenol used is in the range of 1:4 to 1:6. In yet another embodiment the catalyst used is in the range of 1-20 wt% of the diethyl oxalate. In yet another embodiment the Wt ratio of the mixture of diethyl oxalate and phenol to catalyst used is in the range of 100:2 to 100:5. In yet another embodiment the temperature used is in the ranee of 180 to 200°C. In yet another embodiment the selectivity of diphenyl oxalate obtained is 100%. In another embodiment diethyl to phenol molar ratio is 1:5. In yet another embodiment mixture of diethyl oxalate and phenol to catalyst weight ratio is 100:3. In still another embodiment of the invention, the reaction is conducted at temperature ranging from 160 to 220 °C. In still another embodiment of the invention, the heterogeneous catalyst is recovered and recycled. The present invention provides a high selectivity process for the preparation of diphenyl oxalate by transesterification of diethyl oxalate with phenol over silica supported molybdenum oxide (MoO3/SiO2) solid acid catalyst. The MoO3/SiO2. catalyst used in present invention is prepared by sol-gel technique with molybdenum oxide in the range of 1 to 20 wt % of silica using ammonium molybdate as molybdenum source and ethyl silicate-40 as silica source. The amount of catalyst used in the process varies in the range of 1 to 20 wt %of diethyl oxalate used. The transesterification of diethyl oxalate in the present invention is carried out in 50 ml 2-necked round bottom flask fitted with distillation apparatus and thermometer. The top of the distillation condenser was maintained at 80 °C to remove the ethanol formed during the reaction to accelerate the reaction to form desired product. The flask was charged with diethyl oxalate, phenol and catalyst. The flask was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to desired temperature. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. The reaction mixture was analyzed using GC and the product was confirmed using GC-MS. The process is carried out in a temperature range of 160 to 220 °C more preferably at 180 °C. The present invention provides a catalytic high selectivity process for the transesterification of diethyl oxalate to diphenyl oxalate with a provision for a catalyst separation, recovery, and reuse. The catalyst being insoluble in the reaction medium, it can easily be separated and reused. The catalyst may be reactivated by typical activation method like calcinations etc. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 This example illustrates the preparation of MoO3/SiO2 catalyst. The mole equivalent quantities of ammonium molybdate equivalent to 1, 5, 10, 15, and 20% of MoO3 load was dissolved in 40 gm of distilled hot water. This solution was added dropwise to the dry isopropyl alcohol solution (40 ml) of ethyl silicate- 40 equivalent to 99, 95, 90, 85 and 80 % of SiO2 with constant stirring. The solution was further stirred at room temperature for two hours to partially remove the alcohol. The greenish gel obtained was first dried at room temperature in air and then dried at 100 °C for 12 h. The catalyst was further calcined at 500 °C for 8 h. to obtain the catalysts with 1, 5, 10, 15 and 20 % molybdenum loading. Catalysts were completely characterized by powder X-ray diffraction analysis, BET surface area, temperature programmed desorption of ammonia and FTIR spectroscopy. XRD analysis showed high dispersion of M0O3 on silica surface and no separate MoO3 phase was observed upto 10 % Mo loading. Catalysts with 15 and 20 % MoO3 loading showed high crystallinity with clear peaks corresponding to a-M0O3. The catalysts showed very high surface area and the surface area decreased with increasing M0O3 content. The surface area of 1 % MoO3/SiO2 is 583 m2/g and that of 20 % MoO3/SiO2 is 106 m2/g. The overall acidity of the catalysts was found to decrease with increasing M0O3 content. The ammonia desorption occurred at 400 °C indicating moderate acid strength. The pyridine adsorption using FTIR showed the presence of Lewis as well as Bronsted acidity in all the catalysts. Surface area and NH3-TPD analysis as given in table-1 TABLE-1 (Table Removed) AMPLE-2 The transesterification reaction was performed using a round bottom flask of 50 ml capacity and having two neck openings equipped with a stirrer, a thermometer. The flask was charged with 5.0 gm diethyl oxalate, 19.5 gm phenol and 750 mg 1 % MoO3/SiO2 catalyst. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results- Diethyl oxalate conversion: 85.85 % Selectivity for diphenyl oxalate: 100 % Yield: 85.85% EXAMPLE - 3 Solution of reaction mixture from example 2 was decanted and the catalyst remaining in the flask was used as such for transesterification reaction. To the same flask was added 5.0 gm diethyl oxalate, 19.5 gm phenol. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results- Diethyl oxalate conversion: 79.25 % Selectivity for diphenyl oxalate: 100 % Yield: 79.25% EXAMPLE - 4 The transesterification reaction was performed using a round bottom flask of 50 ml capacity and having two neck openings equipped with a stirrer, a thermometer. The flask was charged with 5.0 gm diethyl oxalate, 19.5 gm phenol and 750 mg 5 % MoO3/SiO2 catalyst. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results- Diethyl oxalate conversion: 73.62 % Selectivity for diphenyl oxalate: 88 % Yield: 64.79 % EXAMPLE - 5 The transesterification reaction was performed using a round bottom flask of 50 ml capacity and having two neck openings equipped with a stirrer, a thermometer. The flask was charged with 5.0 gm diethyl oxalate, 19.5 gm phenol and 750 mg 10 % MoO3/SiO2 catalyst. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results- Diethyl oxalate conversion: 55.92 % Selectivity for diphenyl oxalate: 100 % Yield: 55.92 % EXAMPLE - 6 The transesterification reaction was performed using a round bottom flask of 50 ml capacity and having two neck openings equipped with a stirrer, a thermometer. The flask was charged with 5.0 gm diethyl oxalate, 19.5 gm phenol and 750 mg 15 % MoO3/SiO2 catalyst. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results- Diethyl oxalate conversion: 55.92 % Selectivity for diphenyl oxalate: 100 % Yield: 55.92% EXAMPLE - 7 The transesterification reaction was performed using a round bottom flask of 50 ml capacity and having two neck openings equipped with a stirrer, a thermometer. The flask was charged with 5.0 gm diethyl oxalate, 19.5 gm phenol and 750 mg 20 % MoO3/SiO2 catalyst. The mixture was flushed with nitrogen for 10 min to remove the air from the reaction system. The reaction mixture was heated to 180 °C. As the reaction proceeded ethanol formed was distillated out. The reaction was stopped after 5 h. Results-Diethyl oxalate conversion: 55.55 % Selectivity for diphenyl oxalate: 100 % Yield: 55.55% The main features of this high selectivity process are use of diethyl oxalate as precursor for preparation of diphenyl oxalate and very high selectivity, almost 100 % for diphenyl oxalate. The formation of diphenyl oxalate is one step process in this case as no ethyl phenyl oxalate is formed during the course of the reaction. The main advantages of the present invention are 1. High conversion of diethyl oxalate 2. Very high selectivity for diphenyl oxalate 3. No formation of ethyl phenyl oxalate which is the drawback of the previous processes 4. Catalyst recovery and recycle We claim: 1. An improved process for the preparation of high selective diphenyl oxalate, which comprises; reacting diethyl oxalate with phenol in the presence of Mo03/Si02 solid acid catalyst wherein the ratio of Moo3 to Si02 is in the range of 1:99 to 2090, in an inert atmosphere, at a temperature in the range of 160 to 250°C, for a period of at least 5 hrs to obtain the resultant mixture containing diphenyl oxalate, distilling the above said resultant reaction mixture successively in fraction to obtain the enriched diphenyl oxalate in high yield. 2. An improved process as claimed in claim 1, wherein the mole ratio of diethyl to phenol used is in the range of 1.4 to 1:6. 3. An improved process as claimed in claims 1-2, wherein the catalyst used is in the range of 1-20 wt% of the diethyl oxalate. 4. An improved process as claimed in claims 1-3, wherein the Wt ratio of the mixture of diethyl oxalate and phenol to catalyst used is in the range of 100:2 to 100:5. 5. An improved process as claimed in claims 1-4, wherein the catalyst used is recovered and is recyclable. 6. An improved process as claimed in claims 1-5 wherein the temperature used is in the range of 180 to 200°C. 7. An improved process as claimed in claims I-6,wherein the selectivity of diphenyl oxalate obtained is 100%.

Documents:

785-DEL-2005-Abstract-(17-03-2012).pdf

785-del-2005-abstract.pdf

785-DEL-2005-Claims-(17-03-2012).pdf

785-del-2005-claims.pdf

785-DEL-2005-Correspondence-Others-(17-03-2012).pdf

785-del-2005-correspondence-others.pdf

785-del-2005-description (complete).pdf

785-del-2005-form-1.pdf

785-del-2005-form-18.pdf

785-del-2005-form-2.pdf

785-DEL-2005-Form-3-(17-03-2012).pdf

785-del-2005-form-3.pdf