Benzoquinone imines. Part 14. The kinetics and mechanism of the coupling of p-benzoquinone monoimines with m-aminophenols

Abstract

The coupling of p-benzoquinone monoimines with m-aminophenols involves rate-controlling electrophilic attack of the p-benzoquinone imine and/or its conjugate acid on the 4-carbon atom of the m-aminophenolate ion to give the corresponding aminodihydroxydiphenylamine. The latter undergoes rapid oxidation to afford the 2-aminoindo-phenol [2-amino-N-(4-hydroxyphenyl)-p-benzoquinone monoimine]. In concentrated solution, if the 2-amino-indophenol has no substituent in the 5-position, addition of p-aminophenols to give a trinuclear species occurs. The effect of methyl and chloro substituents on the reactivity of the imine and m-aminophenol, and on the spectrum of the 2-aminoindophenol are discussed.