Activation parameters and mechanism of the deamination of N-substituted quinone monoimines and di-imines

Abstract

The deamination rates of six N-substituted quinone monoimines in aqueous solution were measured by a stopped-flow method at temperatures between 278 and 323 K in the pH range between 1 and 9 using u.v. spectra. The observed rate constants are given by k=k′[H₂O]+k″[OH^–]; k′ and k″ differ by 12 orders of magnitude. The enthalpies of activation of k′ and k″ are nearly equal; the entropies of activation are strongly negative for k′ and strongly positive for k″. The activation parameters of the acid and alkaline deamination of N-substituted quinone di-imines were also measured. With regard to the activation entropies similar results were found as for the quinone monoimines. For all deaminations a common mechanism with a preceding solvation equilibrium is proposed.