Photoelectrochemical reduction of meta-halonitrobenzenes and related species

Abstract

Dual photo- and electro-chemical activation of m-chloronitrobenzene and m-bromonitrobenzene in acetonitrile solution leads to halide loss through a photo-ECE mechanism. This proceeds via absorption of visible light by the radical anions [X-C₆H₄NO₂]˙^–, which is followed by fragmentation forming the C₆H₄NO₂ aryl radical. The latter reacts with the solvent system forming nitrobenzene which is further reduced at the electrode with the generation of [C₆H₅NO₂]˙^–. Reduction of m-iodonitrobenzene leads to iodide loss without the need for irradiation. However, this process is accelerated by visible light. In contrast the dual activation of p-cyanonitrobenzene, p-dinitrobenzene, phenyl 4-nitrophenyl sulfone, methyl 4-nitrophenyl sulfone, phenyl 4-nitrophenyl sulfoxide or methyl 4-nitrophenyl sulfoxide failed to induce the leaving of any substituent suggesting that the process may be selective to halo-compounds.