Process for the preparation of thiophene-2-5-dicarboxylic acid and the dichloride thereof

Abstract

The invention relates to a process for the preparation of thiophene-2,5-dicarboxylic acid by reacting thionyl chloride and adipic acid, with pyridine as catalyst, which process comprises A) adding 1 part of adipic acid to 3 to 6 parts of thionyl chloride, mixed with a catalytic amount of pyridine, B) adding a further 4 to 7 parts of thionyl chloride in the temperature range from 85.degree. to 95.degree. C., C) removing excess thionyl chloride and volatile by-products under reduced pressure, and D) bringing the reaction to completion in the temperature range from 140.degree. to 160.degree. C., and E) preparing a salt of thiophene-2,5-dicarboxylic acid by hydrolysing the chloride obtained with an aqueous solution of an alkaline earth metal hydroxide or an alkali metal hydroxide, and F) obtaining the free acid from this salt with a mineral acid.

Dependencies are inferred from the claim text.