Electron transfer reactions. A reinvestigation of the chlorination of 1-methyl-2-phenylindole with N-chlorobenzotriazole. The role of oxygen and oxygenated solvent

Abstract

1-Methyl-2-phenylindole (1, MPI-H) reacts with N-chlorobenzotriazole (2, BT-Cl) to form the corresponding radical cation (MPI-H)˙+ which itself, or via the indolyl radical (MPI)˙+, formed by deprotonation of MPI-H˙+, reacts with oxygen or a nucleophilic solvent leading to indoxyls 4–7. Cyclic voltammetric studies, as well as the oxidation of MPI-H with BT-Cl carried out in the EPR cavity, show that the radical cation MPI-H˙+ dimerizes to give 3,3′-(MPI)28 which is transformed into the corresponding radical cation 3,3′-(MPI)2˙+ in the reaction medium. The identity of this radical cation has been confirmed by oxidizing 3,3′-(MPI)2 directly. The formation of the radical cations MPI-H˙+ and 3,3′-(MPI)2˙+ has been monitored by UV–VIS spectroscopy and their decay rate constants measured.