Sulphonation of arylpyrazoles. Part II. Some 1-phenylpyrazolesulphonic acids and their derivatives

Abstract

1-Phenylpyrazole is sulphonated by oleum principally in the para-position of the phenyl nucleus, whereas chlorosulphuric acid in chloroform solution sulphonates it in the 4-position of the pyrazole nucleus. By increasing the severity of the conditions, substituents can be introduced at both reactive sites to give disubstituted derivatives. The chemical evidence for the structures of these compounds is supported by n.m.r. spectra.