The chemistry of some triphenylmethane dyes

Abstract

A comprehensive series of Pyrrole Green dyes containing substituents in the 2-, 3- and 4-positions of the phenyl ring have been synthesised from the relevant carbinols. The steric and electronic effects of the substituents on the visible absorption spectra of the dyes have been examined and linear correlations between A max and appropriate Hammett substituent constants have been established. The rates of hydrolysis of the 4-diethylamino substituted analogue of Pyrrole Green and some 4 1 ,4 11 -bis(N-ethyl-N- 2,2, 2-trifluoroethyl)aminotriphenylmethyl dyes have been studied under a range of different reaction conditions. A stopped-flow technique was used for the study of the fast reactions involved with these dyes. The results from the spectral investigation and the kinetic work indicate that the Pyrrole Green dye series is relatively unstable compared to other related dyes and the reasons for this behaviour are discussed. Pyrrole, pyrrolidine and diethylamino groups have been incorporated into the 2-, 3- and 4-positions of the phenyl ring of Brilliant Green. Spectral characteristics and kinetic data have been examined for the dyes and relevant substituent constants interpolated. The results are discussed in relation to the steric and electronic effects of the heterocyclic moieties. The rate data obtained for each dye studied have been used to derive thermodynamic activation parameters and to test the applicability of an isokinetic relationship in the systems. A novel reaction pathway for the synthesis of pyrroloindoles from 2-pyrrol-l-yl substituted dyes is advanced