Direct and catalyzed electrochemical syntheses in microemulsions

A series of electrochemical reductions were carried out in microemulsions w ith a view to determining the utility of these novel fluids for preparative electrochemistry. Direct reduction of nitrobenzene in a microemulsion of d idodecyldimethylammonium bromide (DDAB), hexane, and water gave azoxybenzen e as the product. With HCl in the water phase, azoxybenzene and azobenzene were produced. This, together with spectroscopic results, demonstrates that nitrobenzene resides in a polar region of low proton availability. Reducti on of aryl iodides and aromatic hydrocarbons in microemulsions resulted in clean reductive cleavage of the carbon-iodine bond, followed by reduction o f the aromatic rings. Doubly electrocatalytic reduction of benzal chloride to toluene was also accomplished by using various cobalt complexes in a DDA B microemulsion. Cyclization of a cyclohexenyl bromoacetal (24) gave an uns aturated bicyclic product (25) at low potentials with simultaneous irradiat ion by visible light using a 0.2 ratio of vitamin B-12 to reactant in a cet yltrimethylammonium bromide (CTAB) microemulsion and in organic solvents. U sing a 0.01 ratio of catalyst to reactant and - 1.8 V, production of the co rresponding saturated bicyclic product (26) was found in the microemulsion, but not in organic solvents. Results suggest new possibilities for synthet ic pathway control using microemulsions. (C) 1999 Elsevier Science Ltd. All rights reserved.