CS232954B1 - Process for the preparation of 2-methyl-4,5-diphenylthiazole - Google Patents

Abstract

Bromination of desoxybenzoin and condensation of its bromo derivative with thioacetamide in such a way that the bromination is carried out in chloroform or another inactive and water-immiscible solvent with a boiling point in the range of 30 to 100 °C, the obtained solution of the bromo derivative is neutralized, thioacetamide is added to it, the mixture is stirred at a temperature of 10 to 50 °C and then at the boiling point of the reaction mixture until the reaction is complete, concentrated hydrochloric acid is added, after subsequent distillation of the solvent used, the crystallized hydrochloride of the product is suctioned off from the residue and washed with benzene, after venting the benzene is converted to a base by heating and excess aqueous ammonia or aqueous alkali hydroxide solution and the crystallized product is isolated by cooling. Effective preparation of 2-methyl:-4,5-diphenylthiazole for its use as a semi-finished product in the production of photographic sensitizers.

Description

By bromination of desoxybenzoin and condensation of its bromo derivative with thioecetamide by bromination in chloroform or other inactive and water-immiscible solvent boiling in the range of 30 to 100 ° C, the obtained bromo derivative solution is neutralized, thioacetamide is added, After stirring at 10 to 50 ° C and then at the boiling point of the reaction mixture until completion of the reaction, concentrated hydrochloric acid is added, after distilling off the solvent used, the crystallized hydrochloride of the product is filtered off with suction and washed with benzene. excess aqueous ammonia or aqueous alkaline hydroxide solution and cooling the crystallized product is isolated.

Effective preparation of 2-methyl: -4,5-diphenylthiasol for its use as a semi-finished product in the production of photographic sensitizers.

32954

33 9 5 4

The invention relates to a process for the preparation of 2-methyl-4,5-diphenylthiazole of the formula

from desoxybenzoin. It is used as the main semi-finished product for the production of photographic sensitizers. The substance is prepared by bromination of desoxybenzoin in acetic acid, and the resulting bromo derivative is condensed in chlorobenzene with thioacetamide. After removal of the chlorobenzene, the product is isolated by alkalization, shaking into solvent and distillation under vacuum (FIAT final report 943), (p. 43) ·

It has now been found that the above-mentioned substance is more preferably prepared by carrying out the bromination of desoxybenzoin in chloroform or another inactive and water-immiscible solvent boiling in the range of 30 to 100 ° C, such as methylene chloride, tetrahydrofuran, ethylene chloride. , diethyl ether and the like, the bromo derivative formed without isolation after neutralization of the reaction solution, preferably sodium bicarbonate, is first stirred with equimolar or up to 50% thioecetemide to form a precipitate and then heated to dissolve. After addition of concentrated hydrochloric acid in an equimolar or up to 10-fold amount, all solvent is distilled off from the mixture. Benzene is added to the residue and the hydrochloride of the product is crystallized on cooling. After exhaustion with a benzene wash, the latter is vented from benzene, melted in water with the addition of excess ammonia or alkaline hydroxide. The oily precipitated bases were allowed to solidify by cooling, filtered off with suction, washed with water and air-dried.

In the present invention, the use of toxic chlorobenzene, a large amount of unusable acetic acid, is eliminated and the reaction is carried out at lower temperatures. Without solvent extraction and vacuum distillation, a pure and easy to use product is obtained immediately.

The examples below illustrate the prior art and embodiments of the invention.

Example 1 kg of desoxybenzoin is dissolved in 5 liters of glacial acetic acid and accumulates with a solution of 0.81 kg of bromine in 1 liter of glacial acetic acid. The brominated product is not poured onto 15-20 kg of ice and extracted with three liters of chlorobenzene. The dried chlorobenzene solution is slowly heated with 0.403 kg of thioacetamide for about 1 hour. The temperature is raised to 25 DEG-130 DEG C. and water and chlorobenzene are distilled off. To the residue were added 5 liters of water and 2.5 liters of hydrochloric acid, and the chlorobenzene was steamed out. The residue was basified and the thiazole was extracted with methylene chloride. After distillation under reduced pressure, the product is obtained as a slowly crystallizing oil. Yield 0.8 kg, i.e. 62.5% of theory.

Example2 •

00 parts by weight were dispersed in 400 parts by volume of dry chloroform. parts of desoxybenzoin and brominated at a temperature of about 40 ° C by the addition of a solution of 78.5 wt. parts of bromine in 100 parts by volume of chloroform. After complete bromination, the reaction solution was poured into 1000 parts by volume of water and several times

Washing with water several times frees the acid. Then 40 wt. parts of thioacetamide, heated to 25 ° C and stirred until a precipitate formed. Then, the reaction mixture is boiled to dissolution,-125 parts by volume of concentrated hydrochloric acid is added, and all chloroform is distilled off from the reaction mixture. 50 parts by volume of benzene are added to the remaining solution, cooled in an ice bath and allowed to crystallize. Crystals

232 9 5 4 are aspirated and washed with benzene. The obtained colorless crystal cake was degassed by venting benzene, poured 200 volumes of water, heated to 70 ° C, added 150 volumes of concentrated aqueous ammonia, stirred well and allowed to set. The solidified product is separated, crushed, rinsed with water and air dried. 100 wt. m.p. 51-52 ° C. Yield: 78%. The same results are obtained with methylene chloride, ethylene chloride, carbon tetrachloride and diethyl ether.

Claims (1)

SUBJECT OF THE INVENTION A process for the preparation of 2-methyl-4,5-diphenylthiazole of the formula (C-CH3 _{) by} bromination of desoxybenzoin and condensation of its bromo derivative with thioacetamide, characterized in that the bromination is carried out in chloroform or other inactive medium with a water-immiscible solvent. 30 to 100 ° C as methylene chloride, carbon tetrachloride, ethylene chloride, diethyl ether, the obtained bromo derivative solution is neutralized, preferably with sodium hydrogen carbonate, added with an equimolar or up to 50% increased amount of thioacetamide, the mixture is stirred at 10 to 50 ° C preferably at 25 ° C until a precipitate is formed and then at the boiling point of the reaction mixture until completion of the reaction, an equimolar or up to 10-fold concentrated hydrochloric acid is added, after distilling off the solvent used, the crystallized hydrochloride of the product is suctioned off vent and the rest melts the excess crystallized product is suctioned off and washed with benzene, after the benzene has been vented, is converted by heating with an excess of aqueous ammonia or aqueous alkaline hydroxide solution, and the crystallized product is isolated by cooling.