A study of the reactions of C-nitroso compounds with base by means of electron spin resonance spectroscopy

Abstract

The radical-anions of various nitrosoarenes were generated using bases or by electrochemical reduction. The radical-anions of 2,6 or 2,4,6 chloro- or bromo-nitrosoarenes lost halide from the 2-position and the radical-anion of the resulting nitrosoarene was detected. The chloro- or bromo-nitrosoarenes also formed dimeric radical-anions possibly of a semi-diazoxide structure [ArN(O·)N(O-)Ar]. The radical-anions of fluoro-substituted nitrosoarenes were not detected either through alternative reaction on the ring or because the azoxy-derivative and further reduction products were favoured in the equilibrium with the nitroso-radical-anion. [diagram] The spectra of the radical-anions detected exhibited line-broadening due to slow molecular tumbling and one example was examined in detail.

The reaction between a nitrosoarene and iodoalkane in reducing conditions (basic media or electrochemical reduction) was investigated. The corresponding nitroxide and/or N-alkoxyanilino radical were detected.

With the chloro- and bromo- nitrosoarenes attack by base on the ring probably occurs prior to formation of the anilino radical. The radicals are thought to be generated by nucleophilic substitution at the halide by the nitroso-radical-anion. [diagram] When the reaction is performed in the presence of molecular oxygen the nitro-arene radical-anion generated may also react with iodoalkanes to form a nitroxide. The reaction was extended to the polyhalogenomethanes, tri-iodomethane, di-iodomethane and tribromomethane. Reaction with nitrosobenzene generated N,N'-diphenyl-formamidinyl-N, N'-dioxide: [diagram].