Benzoquinone imines. Part VII. The mechanism and kinetics of the reaction of p-benzoquinone di-imines with monohydric phenols and the ultraviolet, infrared, and nuclear magnetic resonance spectra of the resulting indoanilines

Abstract

The reaction of p-benzoquinone di-imine and its C-methyl and C-chloro-derivatives with monohydric phenols is shown to give indoaniline dyes, by a two-step reaction involving a rate-controlling electrophilic attack of the conjugate acid of the di-imine on both the phenoxide ion and the neutral phenol. The resulting 4-amino-4′-hydroxy-diphenylamine then suffers rapid oxidation by a second molecule of di-imine to give the indoaniline dye. The reactivity of the phenoxide ion is increased by methylation and decreased by chlorination. At a fixed pH the rate of reaction of the di-imine with a particular phenoxide ion is decreased by C-methylation of the di-imine and increased by C-chlorination. These substituent effects have been found to be additive. The u.v., i.r., and n.m.r. spectra of the C-methylated indoaniline dyes are tabulated and shown to indicate that the dyes exist as the N-(4-aminophenyl)-p-benzoquinone monoimines rather than as the N-(4-hydroxyphenyl)-p-benzoquinone di-imines.