Direct and catalyzed electrochemical syntheses in microemulsions

A series of electrochemical reductions were carried out in microemulsions with a view to determining the utility of these novel fluids for preparative electrochemistry. Direct reduction of nitrobenzene in a microemulsion of didodecyldimethylammonium bromide (DDAB), hexane, and water gave azoxybenzene 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. Reduction of aryl iodides and aromatic hydrocarbons in microemulsions resulted in clean reductive cleavage of the carbon-iodine bond, followed by reduction of the aromatic rings. Doubly electrocatalytic reduction of benzal chloride to toluene was also accomplished by using various cobalt complexes in a DDAB microemulsion. Cyclization of a cyclohexenyl bromoacetal (24) gave an unsaturated bicyclic product (25) at low potentials with simultaneous irradiation by visible light using a 0.2 ratio of vitamin B-12 to reactant in a cetyltrimethylammonium bromide (CTAB) microemulsion and in organic solvents. Using a 0.01 ratio of catalyst to reactant and - 1.8 V, production of the corresponding saturated bicyclic product (26) was found in the microemulsion, but not in organic solvents. Results suggest new possibilities for synthetic pathway control using microemulsions. (C) 1999 Elsevier Science Ltd. All rights reserved.