SOURCES OF HYDROGEN IN THE ELECTROCHEMICAL REDUCTION OF IODOBENZENE IN DIMETHYLFORMAMIDE SOLUTION

Iodobenzene has been reduced in dimethylformamide solution containing known amounts of H2O and D2O; both lithium chloride and tetraethylammonium bromide have been used as electrolytes. The deuterium content of the resulting benzene and the known isotope effect have been used to calculate the fraction of benzene protonated by water. The amount of tetraethylammonium ion losing a proton is given by the yields of triethylamine and ethylene. The results indicate that water is by far the best proton donor present. Tetraethylammonium ion is less effective but can furnish significant quantities of hydrogen ion. However, at least a part of this is done indirectly with water serving as the transfer medium. In the absence of adequate amounts of better proton donors dimethylformamide itself can be a hydrogen source, although benzene yields fall off because of side reactions. © 1979, American Chemical Society. All rights reserved.