Title of Invention

AN IMPROVED PROCESS FOR THE NITRATION OF XYLENE ISOMERS USING ZEOLITE BETA CATALYST

Abstract

This invention relates to an improved process for the nitration of xylene isomers by using zeolite-beta as a catalyst. This invention particularly relates to a process for the nitration of xylenes using solid acid catalyst, thus totally eliminating the disposal of spent acid and salts.The process steps comprises : nitrating the xylene isomers with nitric acid in a molar ratio of xylene isomers to nitric acid in the range of 1 : 0.80 to 1: 1.5 in the presence of a zeolite-ß catalyst at a temperature in the range of 90 to 120°C for a period of 3 to 5 hrs, recovering the resulting nitro compounds by conventional methods.

Full Text

This invention relates to an improved process for the nitration of xylene isomers using zeolite-beta catalyst. This invention particularly relates to a process for the nitration of xylenes using solid acid catalyst, thus totally eliminating the disposal of spent acid and salts. Nitration has been an active area of industrial chemistry for over a century. Nitration process is used for the production of many large-volume chemicals such as nitro aromatics. The production of mixtures of aromatic nitro compounds in different isomeric proportions from those usually obtained in direct nitration and the nitration of compounds that are usually obtained in direct nitration and the nitration of compounds that are usually uncreative would be of synthetic importance. These nitro aromatics are vital intermediates for dyes, pharmaceuticals, pesticides, perfumes and pesticides. In nitration, normally 1, 2-disubstituted benzenes often pose more problems of selectivity than do mono substituted benzenes. Nitration of xylenes is performed by the classical method employing the H2SO2 -HNO3 system. The selectivities in the nitration of xylenes using mixed H2SO4 " HNO3 are: 3-nitro-0-xylene and 4-nitro-O-xylene from 0-xylenne are 55% and 45% respectively while that of 2-nitro-m-xylene and 4-nitro-m-xylene from m-xylene are 14% and 86% respectively. The mixed acid system not only displays low isomeric selectivity in the nitration of mono and di substituted aromatic nitro compounds, but also it is corrosive and invariably used in excess that often leads to over-nitrated products or oxidized byproducts. Another major disadvantage of this process is the disposal of the spent acid. Recent attention has been focused on the development of environmentally friendly solid acid catalysts such as zeolites, sulfated zirconia and Nafion especially to perform Friedel-Crafts nitration reactions in an effort to replace environmentally hazardous chemicals. Reference may be made to J. Org. Chem., 1961, 26, 2536 wherein the 4-nitro-o-xylene was prepared by the nitration of o-xylene which is carried out with uranium nitrate-nitrogen tetroxide water complex in acetic anhydride. The drawbacks in the above process are the use of expensive and hazardous metal complexes, large amount of acetic anhydride which forms insitu explosive acylnitrate and the reaction is a highly exothermic reaction. Reference may be made to J. Am. Chem. Soc., 1962, 84, 3684 wherein the nitration of the isomers of xylene was carried out with nitronium salts in tetramethylene sulfone and in nitromethane solution at 20°C. The isomeric distribution of nitrocompounds of o- and m- xylenes with tetramethylene sulfone and nitromethane were 79.7%, 68.6% (3-nitro-o-xylene); 20.3%, 31.4% (4-nitro-o-xylene); 17.8%, 14.6% (2-nitro-w-xylene); 4-nitro-m-xylene: 82.2%, 85.44. The drawback in the above process is the use of high dilutions, use of excess nitrating reagents and it is a homogeneous process. Reference may be made to J. Org. Chem., 1973, 38, 2271 wherein the nitration of o-xylene was induced by the aroyl nitrates prepared from the corresponding aroyl chloride and silver nitrate. The demerits of this process are that the reagents used are uneconomical and expensive metallic salts and also the occurrence of benzoylation in addition to nitration. Reference may be made to J. Am. Chem. Soc., 1974, 96, 2892 wherein the nitration of xylenes was catalysed by BF3. The isomer distribution of the nitro products are: 4-nitro-o-xylene 34.7%; 3-nitro-o-xylene 65.3% in nitration of o-xylene; 2-nitro-w-xylene 16.9%; 4-nitro-w-xylene 83.1%in nitration of m-xylene. The disadvantages of this process was that it is a homogeneous and the yields are relatively low. Reference may be made to J. Chem. Soc., Perkin Trans. 1, 1974, 1751 wherein the nitration of o- and m-xylene was performed by the nitrato-complexes of zirconium (IV) and iron(III) at room temperature. The selectivities in this process are: 4-nitro-o-xylene (65%) and 3-nitro-o-xylene (35%) in nitration of o-xylene ; 2-nitro-w-xylene 10% and 4-nitro-w-xylene 90% in nitration of m-xylene with Zr(NO3)4 and with Fe(NO3)4NO respectively. The demerit of this process was the expensive of nitrating agents. Reference may be made to J. Chem. Soc., Perkin Trans. 1, 1978, 1076 wherein the nitration of o-xylene was performed with sodium nitrite or nitrate in triflouroacetic acid at room temperature for 8 h with constant stirring. The selectivity of 4-nitro-o-xylene in this process is 47% and 39% with NaNO2 and NaNO2 respectively. The demerits of this process is that it is a hazardous and explosive, non-economical and low selectivity towards 4-nitro-o-xylene. Reference may be made J. Org. Chem., 1978, 38, 4243 wherein the nitration of m- xylene was performed with anhydrous nitric acid and trifluoromethanesulfonic acid using dichloromethane as a solvent. The demerit of this process was that there is no formation of any mononitro isomer of m-xylene (only dinitro derivatives were formed). Reference may be made to J. Org. Chem., 1978, 43, 4628 wherein the nitration was performed with n-butyl nitrate, acetone eyanohydrin nitrate catalyzed by a perfluorinated resin sulfonic acid (Nafion-H) catalyst. The nitrations were also performed with nitric acid and dinitrogen tetroxide over Nafion-H catalyst. The conversion is 98%, 98% and 95% for o-, m- and ß-xylene respectively. The demerits of these processes are the longer reaction times, use of fuming nitric acid and tedious work-up procedure for the reaction with dinitrogen tetroxide and also use of expensive nitrating agents. Further the Nafion - H resin is expensive and degraded for each cycle and eventually the catalyst has short life. Reference may be made to J. Org. Chem., 1981, 46, 2706 wherein the nitration was catalyzed by boron triflouride etherate with N-nitropyrazole using dichloromethane as the solvent. The conversion is 96% for p-xylene. The demerit of this process is the use of excess aromatic compound and a homogeneous process. Reference may be made to J. Org. Chem., 1981, 46, 3533 wherein the nitration was catalyzed with boron triflouride and silver nitrate in acetonitrile solution. The selectivity of the nitro isomers were: 4-nitro-o-xylene 37%, 3-nitro-o-xylene 63% in nitration of o-xylene; 2-nitro-m-xylene - 13% and 5-nitro-m-xylene - 87% in nitration of m-xylene. The demerits of this process are the longer reaction times, difficult reaction conditions and work-up procedures. Reference may be made to J. Chem. Soc., Perkin Trans. 1, 1993, 1591 wherein the nitration of o-xylene is performed under continuous feeding of ozone in the presence of excess of nitrogen dioxide in dichloromethane as a solvent at 0°C. The selectivities of the nitro isomers are: 4-nitro-o-xylene - 46%, 3-nitro-o-xylene - 34% in nitration of o- xylene; 2-nitro-m-xylene - 9% and 4-nitro-m-xylene - 78% in nitration of m-xylene. The demerit of this process is the necessity for continuous feeding of expensive ozone, which is ecofriendly. Reference may be made to J. Org. Chem., 1998,63,8448 wherein the nitration of o-xylene was performed under mild conditions using beta zeolite as a catalyst and a stoichiometric quantity of nitric acid and acetic anhydride. The conversion was 99% with low selectivities. The demerits of this process are the formation of 3,4-dimethyl-l-acetoxybenzene in 23% yield along with the other isomers and the use of acetic anhydride, which forms an explosive mixture with nitric acid. In order to overcome the drawbacks in the use of mixed acid system, we earlier developed a process for the nitration of monosubstituted aromatic hydrocarbons using aluminium silicates as catalysts and nitric acid as nitrating agent. We duly filed patents for this invention in US, Europe and Japan and already granted U.S. Patent no. 6,034,287, in 2000 and European Patent no. 1004570 Al and Japanese Patent no. 95734 A2. In the present invention, we describe the nitration of disubstituted benzenes, all the isomers of xylene, by employing nitric acid and beta zeolite catalyst dispensing the use of acetic anhydride. The reactions were performed at temperatures ranging from room temperature to reflux temperature of the solvent (DCE). Reactions were performed by taking o-xylene and HNO3 in the molar ratio ranging from 0.80 to 1.50. The selectivity of 4-nitro-o-xylene prepared from O-xylene is 68% and that of 4-nitro-m-xylene from m-xylene is 87%. The selectivity of 2-nitro-p-xylene from p-xylene is 100% based on p-xylene consumed when the nitration is performed using xylene and HN03 in the molar ratio of 1: 1.2. Azeotropic removal of Water formed in the reaction and that present in the nitric acid makes the solid acid catalyst reusable. The main objective of the present invention is to provide a process for the nitration of xylene isomers with high selectivity towards 4-nitro o and m-xylenes using zeolite beta catalyst in batch mode. Another objective of the present invention is to provide an improved process for the nitration of xylene isomers with high selectivity towards 4-nitro oO and m-xylenes using modified clay catalysts. Yet another objective of the present invention is the separation of the isomers using standard vacuum distillation and removing the excess of nitric acid acid by conventional method. Yet another objective of the present invention is the azeotropic removal of the water formed during the reaction and that present in the nitric acid and thus permitting the reusability of the solid acid catalyst. Summary of the invention Accordingly the present invention provides an an improved process for the nitration of isomers of xylene with high selectivity towards 4-nitro ortho m-xylenes using a zeolite beta catalyst in batch mode which comprises nitrating the xylene isomers with nitric acid in a molar ratio of xylene isomers to nitric acid in the range of 1 : 0.80 to 1: 1.5 in the presence of a zeolite-ß catalyst at a temperature in the range of 90 to 120°C for a period of 3 to 5 hrs, recovering the resulting nitro compounds by conventional methods. In an embodiment of the present invention the nitric acid used is added in a controlled manner during the period specified. In yet another embodiment the nitric acid used is about 70% nitric acid. In yet another embodiment the ratio of xyline to nitric acid used is preferably in the range of 1:1.0 to 1:1.25. In yet another embodiment the solvent used for the reaction is selected from the group consisting of dichloroethane, dichloromethane, carbon tetrachloride and xylene itself. hi still another embodiment the reaction is effected at a temperature preferably in the range of 90 to 120 °C for about 4 h. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example 1 50 mmol of o-xylene and 500 mg of catalyst are taken in a 100 ml two-necked round bottomed flask alongwith 10 ml of dichloroethane and heated to reflux temperature. 4.23 ml of HNOs (70%) is added continuously over a period of 4 h. The water formed in the reaction is separated by a Dean-Stark apparatus. On completion of the reaction, the reaction mixture is filtered. It is subjected to base wash to remove the excess acid. The isomers formed are separated by vacuum distillation. Varying the rate of addition of nitric acid, a number of nitration of o-xylene reactions were conducted and summarized in the table 1. The optimum rate of addition of nitric is found to be 1 ml/hour. 1. TABLE: I Nitration of O-xvlene with 70% HNO3:1 (Table Removed) a: molar ratio of o-xylene to 70% HNO3 is 1:1.25; b: molar ratio of o-xylene to 70% HNO3 is 1: 1.2 c: excess of starting material is taken 1: all the reactions were performed at reflux temperature. Conversion is at a maximum of 40% Example 2 50 mmol of m-xylene and 500 mg of catalyst are taken in a 100 ml two-necked round bottomed flask alongwith 10 ml of dichloroethane and heated to reflux temperature. 4.23 ml of HNO3 (70%) is added continuously over a period of 4 h. The water formed in the reaction is separated by a Dean-Stark apparatus. On completion of the reaction, the reaction mixture is filtered. It is subjected to base wash to remove the excess acid. The isomers formed are separated by vacuum distillation. Example 3 50 mmol of p-xy\ene and 500 mg of catalyst are taken in a 100 ml two-necked round bottomed flask alongwith 10 ml of dichloroethane and heated to reflux temperature. 4.23 ml of HNO3 (70%) is added continuously over a period of 4 h. The water formed in the reaction is separated by a Dean-Stark apparatus. On completion of the reaction, the reaction mixture is filtered. It is subjected to base wash to remove the excess acid. The isomers formed are separated by vacuum distillation. The main advantages of the present invention are 1. The present process is very simple. 2. The catalyst is cheap, non-corrosive and heterogeneous in nature. 3. Lesser quantity of nitric acid is employed. 4. The process is economical. 5. The process is accomplished in a short time. 6. The amount of effluents formed in this process is minimized. We Claim: 1. An improved process for the nitration of isomers of xylene with high selectivity towards 4-nitro ortho m-xylenes using a zeolite beta catalyst in batch mode which comprises nitrating the xylene isomers with nitric acid in a molar ratio of xylene isomers to nitric acid in the range of 1 : 0.80 to 1: 1.5 in the presence of a zeolite- ß catalyst at a temperature in the range of 90 to 120°C for a period of 3 to 5 hrs, recovering the resulting nitro compounds by conventional methods. 2. An improved process as claimed in claim 1, wherein nitric acid used is added in a controlled manner during the period of 3 to 5 hrs. 3. An improved process as claimed in claims 1 & 2 , wherein the nitric acid used is of 70% nitric acid. 4. An improved process as claimed in claims 1 to 3, wherein the molar ratio of xylene to nitric acid used is preferably in the range of 1:1.0 to 1:1.25. 5. An improved process as claimed in claims 1 to 4 wherein the solvent used for the reaction is selected from the group consisting of dichloroethane, dichloromethane, carbon tetrachloride and xylene itself. 6. An improved process as claimed in claims 1 to 5, wherein the xylene isomer used is selected from o-xylene, m-xylene and ß-xylene. 7. An improved process for the nitration of isomers of xylene using a zeolite beta catalyst as herein described with reference to the examples accompanying this specification.

Documents:

1308-del-2001-abstract.pdf

1308-del-2001-claims.pdf

1308-del-2001-correspondence-others.pdf

1308-del-2001-correspondence-po.pdf

1308-del-2001-description (complete).pdf

1308-del-2001-form-1.pdf

1308-del-2001-form-18.pdf

1308-del-2001-form-2.pdf

1308-del-2001-form-3.pdf