Birch-Type Reductions in Aqueous Media: Benzothiophene and Diphenyl Ether

Article abstract of DOI:10.1021/jo00368a012

The preparative cathodic reductions of benzothiophene and diphenyl ether were investigated.Aqueous and mixed organic-aqueous solutions of tetrabutylammonium salts served as electrolytes, and the cathode was a mercury pool.Experiments were carried out at a constant current and the products were isolated and identified.It was found that benzothiophene is initially reduced to 2,3-dihydrobenzothiophene, which is subsequently reductively cleaved to 2-ethylbenzenethiol.If the amount of charge transferred is controlled, it is possible to form the dihydro derivative or the cleaved benzenethiol as major product.The cathodic product of diphenyl ether was found to be a mixture of bis(2,5-dihydrophenyl) ether (ca.50percent) and phenol (ca.30percent).The first product is of particular interest since phenol and benzene are the only products of diphenyl ether obtained by reductions involving solvated electrons.The mechanism of reduction of the two reactants is discussed, and possible pathways for the formation of the various products are proposed.