Effect of Basicity of Heterocyclic Nitrogen on the Conversion of Heteroaromatic Carboxylic Acids to Corresponding Trichloromethyl Compounds

Abstract

Some of imidazole- and pyridine-carboxylic acids were reported in the previous paper to be converted to the corresponding trichloromethyl compounds by their reaction with phosphorus pentachloride in excess of thionyl chloride. In the present work, carboxyl groups of 4-chloropicolinic acid and 6-methylpicolinic acid were also converted to trichloromethyl groups under the similar condition, while those of 3-chloropicolinic acid, 6-chloropicolinic acid, pyrazine-2, 5-dicarboxylic acid, pyrimidine-4, 6-dicarboxylic acid and pyridazine-3, 6-dicarboxylic acid failed in the conversion, only giving the corresponding carbonyl chlorides.
The differences in reactivity of these carboxylic acids were studied in connection with the basicities of the heterocyclic nitrogens, and it was found that the acids with pK, higher than about 3.5 were successfully converted to the trichloromethyl derivatives.