Redox and Acidity Properties of Alkyl- and Arylamine Radical Cations and the Corresponding Aminyl Radicals

Abstract

In this work the pKas of six alkyl- and arylamine radical cations in aqueous solution have been determined by means of laser flash photolysis. The corresponding N-nitrosamines were used as precursors for the aminyl radicals which, upon protonation, formed the amine radical cations. The following pKas were obtained: 3.6 ± 0.2, 7.6 ± 0.3, 6.8 ± 0.5, 5.3 ± 0.5, 5.5 ± 0.5, and 5.8 ± 0.5 for the radical cations of diphenylamine, N-methylaniline, dimethylamine, diethylamine, pyrrolidine, and piperidine, respectively. In addition, the peak oxidation potentials of diphenylamine, N-methylaniline, aniline, diethylamine, pyrrolidine, and piperidine have been measured in aqueous solution and in acetonitrile using cyclic voltammetry. Furthermore, the one-electron reduction potentials of the diphenylaminyl radical and the N-methylanilinyl radical in acetonitrile were measured using photomodulation voltammetry. The results of this study and of previously published studies are discussed in terms of relative substituent ...