METHOD FOR THE PREPARATION OF 2,3,5-TRIMETHYLBENZOQUINONE

Abstract: 2,3,5-trimethyl-p-benzoquinone is prepared advantageously by the catalytic oxidation of 2,3,5- or 2,3,6-trimethylphenol with hydrogen peroxide in an organic solvent, which is preferably acetic acid, in the presence of a catalyst which is a heteropolyacid having a silicon or phosphorus atom as the centre atom, selected from phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid and silicotungstic acid. The reaction proceeds rapidly even at room temperature to give the product in a high yield so that the method is industrially advantageous in addition to the advantages in respect of the inexpensiveness of the reactions and catalyst and the absence of any noxious by-products which may cause environmental pollution.

Description: The present invention relates to a method for the preparation of 2,3,5-trimethylbenzoquinone and more particularly, to an efficient method for the preparation of 2,3,5-trimethylbenzoquinone by the oxidation of 2,3,5- or 2,3,6-trimethylphenol in the presence of a specific catalyst. As is known, 2,3,5-trimethylbenzoquinone is an important organic compound which is useful as a starting material in the synthesis of vitamin E and other valuable chemicals. One of the conventional methods industrially used for the preparation of 2,3,5-trimethylbenzoquinone includes the steps of sulfonation of 2,3,6-trimethylphenol as the starting material and oxidation of the sulfonation product using manganese dioxide (see, for example, West German Patents Nos. 1,932,362 and 2,225,543) as an oxiding agent. Although 2,3,6-trimethylphenol is an inexpensive material manufactured by the orthomethylation of m-cresol, or by the oxidation of pseudocumene and is available in large quantities, the above mentioned process for the manufacture of 2,3,5-trimethylbenzoquinone has problems in respect of the by-product to be disposed of as a waste material and the relatively high production cost. Alternatively, it is also known that 2,3,5-trimethylbenzoquinone can be prepared by the direct oxidation of 2,3,5- or 2,3,6-trimethylphenol and many attempts and propsals have been made hitherto in connection with the selection of the oxidizing agent and the catalyst for the oxidation reaction. Examples of oxidizing agents proposed so far include nitric acid taught in Japanese Patent Publication 56-95145, perbenzoic acid taught in Japanese Patent Publication 59-39847 and hypohalogenous acids taught in Japanese Patent Publication 60-81135. These methods also are not quite satisfactory as industrial methods because of the evolution of toxic gases, the expense of the oxidizing agent and the formation of by-products. It is also known that hydrogen peroxide can be used as the oxidizing agent and this method is the most promising industrial method because hydrogen peroxide is relatively inexpensive and the by-product formed from the oxidizing agent is water alone without any problems of environmental pollution. The oxidation of 2,3,5- or 2,3,6-trimethylphenol with hydrogen peroxide to give 2,3,5-trimethylbenzoquinone is promoted by a catalyst and a method is known to use a salt of a metal such as ruthenium and the like (see, for example, Tet. Lett., volume 24 (1983), page 5249 and European Patent Application 107176). This method is, however, disadvantageous due to the expense of the rare metal used in the catalyst and the relatively low yield of the desired product. We have now developed a novel and efficient method for the preparation of 2,3,5-trimethylbenzoquinone by the oxidation of 2,3,5- or 2,3,6-trimethylphenol with hydrogen peroxide as the oxidizing agent in the presence of a catalyst. Accordingly, the present invention provides a method for the preparation of 2,3,5-trimethylbenzoquinone which comprises oxidizing 2,3,5-trimethylphenol or 2,3,6-trimethylphenol with hydrogen peroxide in a reaction mixture containing as a catalyst a heteropolyacid having a phosphorus or silicon atom as the centre atom and also containing molybdenum or tungsten, or an ammonium or alkali metal salt thereof. As described above, the most characteristic feature of the method of the invention is the use of a heteropolyacid as the catalyst and the desired product of 2,3,5-trimethylbenzoquinone is obtained easily merely by agitating a reaction mixture containing the starting material, oxidizing agent and catalyst in an organic solvent under mild conditions, so that the method is industrially advantageous because the process is simple and without any danger. The hydrogen peroxide used as the oxidizing agent in the method of the invention is used in the form of an aqueous solution. The concentration of the aqueous solution of hydrogen peroxide is not particularly limited and commercially available solutions containing 30% by weight of hydrogen peroxide are suitable. Aqueous solutions containing hydrogen peroxide in a higher concentration of 50 to 60% can also be used. The amount of the hydrogen peroxide used in the method of the invention is usually in the range of from 1 to 30 times or, preferably, from 2 to 10 times the stoichiometric amount required for the reaction. The heteropolyacid used as the catalyst in the invention method is exemplified by silicomolybdic acid, silicotungstic acid, phosphomolybdic acid and phosphotungstic acid. Salts of these acids such as ammonium salts and alkali metal salts are also suitable. The amount of the catalyst added to the reaction mixture is 0.05 mole or less or, preferably, in the range of from 0.01 to 0.03 mole per mole of the 2,3,5- or 2,3,6-trimethylphenol as the starting material though not particularly limited. The organic solvent used as the reaction medium in the method of the invention should be miscible with the aqueous solution of hydrogen peroxide as the oxidizing agent in order that the reaction proceeds homogeneously. Examples of suitable organic solvent which are miscible with water include carboxylic acids such as formic, acetic and propionic acids, acetonitrile, methyl alcohol, ethyl alcohol, acetone and N,N-dimethylformamide of which the carboxylic acids such as acetic acid are preferred. The amount of the solvent is such that the concentration of the 2,3,5- or 2,3,6-trimethylphenol as the starting material in the reaction mixture is in the range of from 0.05 to 1.0 mole/liter or, preferable, from 0.1 to 0.5 mole/liter. The concentration of hydrogen peroxide as the oxidizing agent in the reaction mixture is preferably in the range if from 3 to 8% by weight as H₂O₂. The concentration of water, which is unavoidably introduced into the reaction mixture in the form of an aqueous solution of hydrogen peroxide, should not exceed 30% by weight based on the amount of the solvent, although water in a small amount has no particular adverse influence on the course of the reaction. The temperature of the reaction mixture is in the range of from 0 to 70°C or, preferably, from 10 to 35°C and the reaction can proceed with a sufficiently high velocity even at room temperature, requiring no exact control of the temperature. The reaction is usually complete within 1 to 15 hours though dependent on the concentration of the aqueous hydrogen peroxide solution and the amount of catalyst used. As the reaction proceeds the reaction mixture turns yellow. The reaction mixture, after completion of the reaction, is diluted with water and the reaction product is extracted therefrom with a water immiscible organic solvent, such as methylene chloride. The extract is dried over a drying agent such as anhydrous magnesium sulfate and then freed from the solvent by distillation to leave the desired 2,3,5-trimethylbenzoquinone as the product which can be identified by gas chromatography and NMR analysis to give a retention time and NMR spectrum identical, respectively, with those of a standard reagent of 2,3,5-trimethylbenzoquinone. It will be understood from the above description that the method of the invention is advantageous as an industrial process for the manufacture of 2,3,5-trimethylbenzoquinone since the product is obtained from 2,3,5- or 2,3,6-trimethylphenol in a single step reaction in a high yield without the disadvantages of the prior art methods in respect of the waste material product as a by-product, expense of the catalyst and low yield of the product. In the following, the method of the present invention is described in more detail by way of example. The heteropolyacids used in the following experiments as the catalyst include phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid and silicotungstic acid, which are referred to as the catalysts, I, II, III and IV, respectively, hereinbelow. Examples 1 to 4. Into a glass flask were introduced 272 mg (2 m moles) of 2,3,5-trimethylphenol and 100 mg of one of the catalysts mentioned above dissolved in 10 ml of acetic acid and 2 ml of a 60% aqueous solution of hydrogen peroxide were added dropwise to the reaction mixture in the flask. The reaction mixture was agitated for 5 hours in an atmosphere of nitrogen gas at 30 °C. After completion of the reaction, the reaction mixture was diluted with addition of 50 ml of water and extracted three times each with 20 ml of methylene chloride. The extracts as combined were dried over anhydrous magnesium sulfate and analyzed by the gas chromatography for the content of 2,3,5-trimethylbenzoquinone as the product. The results are shown in the table below which includes the % reaction, i.e. % of the reacted starting material, yield in %, i.e. the amount of the product relative to the reacted starting material, and selectivity in %, i.e. % of the reacted starting material converted into the desired product. Examples 5 to 8. The experimental procedure was substantially the same as in the preceding examples except that the reaction time was 3 hours instead of 5 hours. The results are summarized in the table. Examples 9 to 12. The experimental procedure was substantially the same as in Examples 1 to 4 except that the concentration of the aqueous hydrogen peroxide solution was 30% instead of 60%. The results are summarized in the table. Comparative Examples 1 to 3. The experimental procedures in Comparative Examples 1, 2 and 3 were substantially the same as in Example 1. Example 9 and Example 9, respectively, excepting omission of the phosphomolybdic acid, replacement of the phosphomolybdic acid with 100 mg (0.56 m mole) of orthomolybdic acid monohydrate and replacement of the phosphomolybdic acid with 100 mg (0.40 m mole) of orthotungstic acid, respectively. The results are summarized in the table. Examples 13 to 16. The experimental procedure was substantially the same as in Examples 1 to 4 excepting replacement of the 2,3,5-trimethylphenol with the same amount of 2,3,6-trimethylphenol. The results are summarized in the table. Examples 17 to 20. The experimental procedure was substantially the same as in Examples 13 to 16 except that the concentration of the aqueous hydrogen peroxide solution was 30% instead of 60% and the reaction time was 12 hours instead of 5 hours. The results are summarized in the table. Examples 21 to 24. The experimental procedure was substantially the same as in Examples 17 to 20 except that the reaction time was 5 hours instead of 12 hours. The results are summarized in the table. Comparative Examples 4 to 6. The experimental procedures in Comparative Examples 4, 5 and 6 were each substantially the same as in Example 13, Example 21 and Example 21, respectively, excepting omission of the phosphomolybdic acid, replacement of the phosphomolybdic acid with 7.2 mg (0.04 m mole) of orthomolybdic acid monohydrate and replacement of the phosphomolybdic acid with 10 mg (0.04 m mole) of orthotungstic acid. The results are summarized in the table. Examples 25 to 32. The experimental procedure was substantially the same as in Examples 13 to 16 excepting replacement of the acetic acid with the same amount of formic acid in Examples 25 to 28 and of propionic acid in Examples 29 to 32. The results are summarized in the table.

Claims: 1. A method for the preparation of 2,3,5-trimethylbenzoquinone which comprises oxidizing 2,3,5-trimethylphenol or 2,3,6-trimethylphenol with hydrogen peroxide in a reaction mixture containing as a catalyst a heteropolyacid having a phosphorus or silicon atom as the centre atom and also containing molybdenum or tungsten, or an ammonium or alkali metal salt thereof. 2. A method as claimed in claim 1 wherein the heteropolyacid is phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid or silicotungstic acid. 3. A method as claimed in claim 1 or claim 2 wherein the reaction mixture is a solution of 2,3,5-trimethylphenol or 2,3,6-trimethylphenol, hydrogen peroxide in the form of an aqueous solution and the catalyst in an organic solvent. 4. A method for the preparation of 2,3,5-trimethylbenzoquinone as claimed in claim 3 wherein the organic solvent is miscible with water. 5. A method as claimed in claim 4 wherein the organic solvent which is miscible with water is formic acid, acetic acid, propionic acid, acetonitrile, methyl alcohol, ethyl alcohol, acetone or N,N-dimethylformamide. 6. A method as claimed in any one of the preceding claims wherein the amount of the hydrogen peroxide is in the range of from 1 to 30 times of the stoichiometric amount. 7. A method as claimed in any one of the preceding claims wherein the amount of the catalyst is in the range of from 0.01 to 0.03 mole per mole of the 2,3,5-trimethylphenol or 2,3,6-trimethylphenol. 8. A method as claimed in any one of the preceding claims wherein the reaction mixture is kept at a temperature in the range of from 10 to 35°C. 9. A method as claimed in any one of the preceding claims wherein the reaction mixture contains 2,3,5-trimethylphenol or 2,3,6-trimethylphenol in a concentration in the range of from 0.05 to 1.0 mole/liter.

Inventors: HAYAKAWA, TAKASHI, ORITA, HIDEO, SHIMIZU, MASAO, TAKEHIRA, KATSUOMI
Applicants: JAPAN AS REPRESENTED BY DIRECTOR-GENERAL, AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Application year: 1989
Main classification: C07C46
IPC codes: C07C46, C07C50