Interactions of picric acid with aqueous sodium sulphite and with sodium hydroxide

Abstract

The interactions of picric acid with aqueous sodium sulphite and with sodium hydroxide have been examined by visible and ¹H n.m.r. spectroscopy. There is evidence in concentrated sodium sulphite solutions for the formation of an unusual ion carrying five negative charges. This results from the covalent addition of two sulphite molecules to the picrate ion, at ring carbon atoms carrying hydrogen. At low sulphite concentrations a 1 : 1 picrate–sodium sulphite adduct is produced. The major interaction between the picrate ion and sodium hydroxide results in a 1 : 2 picrate–sodium hydroxide complex formed by the covalent addition of hydroxide ion at two ring positions carrying hydrogen.