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.