CS232616B1 - Preparation method of 2,3,5-trimethylhydroquinone - Google Patents

Abstract

A method of preparing 2,3,5-trimethyilhydroquinone by catalytic hydrogenation of 2,3,5-trimethylbenzodhinone in an organic environment solvent and palladium on the catalyst support characterized in that it is hydrogenated it is converted in the environment of palladium chloride while forming the catalyst in Are you here.

Description

The present invention relates to an improved process for preparing 2,3,5-trimethylhydroquinone by catalytic hydrogenation of 2,3,5-trimethylbemoquinone using a palladium catalyst and an organic solvent.

[2,3,5-Trimethylhydroquinone is an important antioxidant for oils and ointments, a UV stabilizer for rubber and synthetic polymers, as well as an important intermediate for the synthesis of vitamin E. 2,3,5-Trimethylhydroquinone can be prepared by chemical reduction of 2,3 5-trimethylbenzoquinone using a reducing agent, for example sodium dithionite, or catalytic hydrogenation with hydrogen in the presence of a noble metal such as palladium or platinum, in the presence of an organic solvent. For example, U.S. Patent 2,309,051 describes a process for preparing 2,3,5-trimethylhydroquinone in high purity. Catalytic hydrogenation is carried out in the presence of a catalyst which has been prepared by reducing the palladium onto the support outside the reaction mixture and dried. The catalyst thus prepared rapidly loses activity when used repeatedly, resulting in an unbearable increase in reaction time. For example, using 0.045 g of pure palladium per mole of 2,3,5-trimethylbenzoquinone, the reaction time is increased to 420 min in a fifth experiment in acetone as solvent. from the original 120 min. the first time. For other solvents, this is even worse, in methyl isobutyl ketone for 480 min, in tertiary butanol, diisopropyl ether, toluene and ethyl acetate, in the fifth experiment, 2,3,5-trimethylbenzoquinone will not be hydrogenated. From an operational point of view, the loss of catalyst activity is disadvantageous because the reaction time is non-constant (gradually increasing).

The above-mentioned disadvantages are overcome by the process for preparing 2,3,5-trimethylhydroquinone according to the invention, which comprises preparing the catalyst directly in the reaction mixture by reducing the palladium with hydrogen to a support (preferably activated carbon) from a palladium chloride solution. The catalyst thus prepared has a much higher activity than the catalyst prepared outside the reaction mixture and dried as described in the above-mentioned German patent. It can be assumed that the presence of chloride ions in the reaction mixture is responsible for the high activity of the catalyst. When the catalyst is reused, at least an amount of palladium chloride solution is added to the reaction mixture to maintain high catalyst activity. In this way 20 hydrogenations (1 mol 2,3,5-trimethylbenzodhinone feed) were carried out, while maintaining the catalyst high activity, • exhibited a virtually constant reaction time, ranging from 80 to 120 minutes. The catalyst could be used further. The consumption of pure palladium without regeneration per mole of 2,3,5-trimethylbenzoquinone was 0.006 g, according to the process of German patent no. No. 2,309,051 is the consumption of palladium for the same number of experiments with the same 2,3,5-trimethylbenzoquinone feed of 0.036 g, t. j. 6 times higher. This multiple is proportionally increased with the number of experiments using the catalyst again, in 50 experiments it is already 15 times.

In the following, the subject matter of the invention is illustrated by three examples without being limited thereto.

Example 1

In a 2 liter autoclave, 1500 ml of acetone, 150 g (1 mol) of 2,3,5-trimethylbenzoquinone, 98% content, 0.75 ml of a 10% by weight palladium chloride solution and 10 g of activated carbon are charged. The pressure is 0.35 MPa and the temperature is 75 DEG C. The reaction is completed in 80 min, the catalyst is filtered, washed with acetone and ready for further use, and the reaction mixture is distilled off on a column (10 theoretical plates 2/3 of acetone). The acetone distillation is continued until the boiling point of toluene has reached the head of the column, then the contents of the distillation flask are cooled to crystallization, 2,3,5-Trimethylhydrochlnone is filtered off with suction, washed 3 times with 100 ml of toluene and dried. 2,3,5-trimethylhydroquinone is obtained with a content of 98.5% in a yield of 95%.

Example 2

The procedure as in Example 1 was followed, except that the washed catalyst of Example 1 and the addition of 0.065 ml of 10% by weight were used for hydrogenation. palladium chloride solution.

This procedure may be repeated at least 20 times.

Example 3

The procedure as in Example 1, except that ethyl acetate was used as the solvent for hydrogenation instead of acetone. Similar to acetone, the same catalyst can be reused at least 20 times as in Example 2.

Claims (1)

A process for the preparation of 2,3,5-trimethylhydroquinone by catalytic hydrogenation of 2,3,5-trimethylbenzoquinone in an organic solvent and palladium supported catalyst form of the invention, characterized in that the hydrogenation is carried out in a palladium chloride environment while forming the catalyst in situ.