DE685033C - Process for the preparation of the dimethylhydroquinones - Google Patents

Description

Process for the preparation of dimethylhydroquinones The subject of patent 683 908 is a process for the preparation of trimethylhydroquinone (pseudocumohydroquinone), which consists in treating trimethyl-p-quinone (pseudocumoquinone) in an organic solvent with hydrogen in the presence of a hydrogenation catalyst. One can work at ordinary temperature and pressure without difficulty. can be designated.

So far, the reduction of dimethylquinones has been laboriously carried out by the action of sulphurous acid (cf. reports of the German Chemical Society, vol. 18 [1885], pp. 1152 and 2673, and Annalen der Chemie, vol. 215 [1882], p. 169), by treatment with zinc dust and acetic acid. In further working through this invention it was found that the dimethylhydroquinones (xylohydroquinones) can also be prepared analogously from the corresponding methyl-substituted p-quinones by catalytic reduction. There are three isomeric dimethylhydroquinones possible, which according to the following formulas as (cf. reports of the German Chemical Society, Vol. 2o [1887], p. 2396) or by the action of tin chloride and hydrochloric acid (cf. Journal of the American Chemical Society, Vol. 45 [19z3], p. 2199). These processes are not particularly suitable for the preparation of larger amounts of the dimethylhydroquinones, because the work-up of the reaction mixture, in particular the separation of the desired product from the excess and the reaction products of the reducing agent, is laborious. Since the solutions of the dimethyl # hydroquinones to atmospheric oxygen au ß @ neatly sensitive is a. more complicated method of manufacture Connections desired. Attempts were made at an early stage (cf. Comptes Rendus, Vol. 146 [1908], p. 458): to use catalytic reduction as the simplest reduction process, because no residues of the reducing agent (hydrogen gas) or its reaction products remain in the reaction mixture. and the processing is the simplest imaginable. However, under the conditions described using the example of p-xyloquinone (transferring the gaseous quinone over a nickel catalyst at 200 °), poor yields of hydroquinone result in practice because the hydroquinones themselves are further reduced under the reaction conditions mentioned (see Armales de Chimie et de Physique, B. Series, Vol. 16 [igog], p.89 and go). For these reasons, the use of catalytic reduction has hitherto been dispensed with in the reduction of xyloquinones and working with reducing chemicals has been preferred despite the disadvantages described above.

The present invention now consists in special reaction conditions to show how the catalytic reduction of 3-xyloquinones can be carried out, under which one can work in the simplest possible way the corresponding, very pure hydroquinones with almost quantitative yield. The working conditions are not in the vapor phase, but in solution or suspension in one organic solvents and at temperatures below. about 150 °, preferably to work at ordinary temperature. The finding about the choice of the reaction temperature is most surprising compared to the observation (Armales de Chimie et de Physique, a. a. O., p. 89, para. 3) that when working in the gas phase a. Subtract the Temperature below about 200 ° leads to hydrogenation of the nucleus.

The preparations customary for hydrogenations, both noble metal catalysts and those from the series of base metals (for example Raney nickel), can be used as catalysts. The solvent can be, for. B. use alcohol, toluene alcohol or ether. Elevated temperature up to about 150 ° and elevated pressure can be used, but are not necessary. It is therefore preferable to work with yneise at ordinary temperature and pressure: In general, the present- Procedure for hydrogen uptake km consumption of the theoretical amount @, Hydrogen to a standstill by itself. The required amount of catalyst can be kept very low. EXAMPLES 1. 40 g of o-xyloquinone are shaken with H 2 in 750 cc of methanol at room temperature after adding 5 g of 10% palladium carbon. After the solution has decolorized in 45 minutes and the uptake of hydrogen has come to a standstill, the catalyst is filtered off with exclusion of air and the solution is evaporated to dryness in vacuo in a CO 2 atmosphere. After recrystallization from water, the o-xylohydroquinone from S.mp. is obtained in a yield of 38 g. 222 °.

2. A solution of 1979 m-xyloquinone in 2 l of methanol is shaken with H2 at room temperature in the presence of 100% palladium-on-carbon. The H2 uptake stops after an hour. After filtering off the catalyst, the solution is evaporated to dryness in a C02 atmosphere in vacuo. After recrystallization from water, m-xylohydroquinone with a melting point of 151 ° is obtained in a yield of 990.16.

3. 111 g of p-xyloquinone are dissolved in 1 l of methanol and in the presence shaken from 100% palladium carbon at 40 ° with hydrogen. In 10 minutes is the calculated amount of hydrogen gas absorbed. After filtering off the catalyst the methanol is evaporated off in vacuo (under CO 2) and the p-xylohydroquinone is removed Recrystallized methanol. The yield b @ is 105 g with a melting point of 215 °.

Claims (1)

PATENT CLAIM: Process for the production of dimethylhydroquinones by catalytic reduction of the corresponding xyloquinones according to patent 683 9o8, characterized in that the xyloquinone in one. organic solvents at temperatures below about 150 °, expediently at ordinary temperature and ordinary pressure, with hydrogen in the presence of a hydration catalyst treated.