RADICALS AND CARBANIONS AS INTERMEDIATES IN THE ELECTROCHEMICAL REDUCTION OF 1-IODODECANE AT MERCURY - EFFECT OF POTENTIAL, ELECTROLYSIS TIME, AND WATER CONCENTRATION ON THE MECHANISM

Polarograms for 1-iododecane in dimethylformamide containing 0.1 F tetramethylammonium perchlorate and 0.050 M water exhibit two waves, with a prominent maximum appearing on the rising portion of the second wave. At potentials positive with respect to the maximum, 1-iododecane undergoes one-electron reduction to yield decyl radicals which become adsorbed onto the mercury cathode; two adsorbed decylmercury radicals interact to give didecylmercury, the only electrolysis product obtained in this potential region. At potentials negative of the maximum, chronocoulometry, cyclic voltammetry, and pulse polarography have revealed that reduction of 1-iododecane on a short time scale is a two-electron process; however, when 1-iododecane is subjected to comparatively slow controlled-potential electrolysis at these potentials, the coulometric n value is unity. Experiments done with deuterium-labeled trapping agents have confirmed that the decyl carbanion is the predominant intermediate at potentials negative of the maximum, although some decyl radicals are formed. At potentials negative of the maximum, the water content of the supporting electrolyte-solvent system as well as the electrolysis time greatly influences the reduction of 1-iododecane. In the presence of 0.050 M water, electrolytically generated decyl carbanions are protonated by water to yield hydroxide ion and decane, the hydroxide attacks unreduced alkyl iodide to give 1-decene and 1-decanol via E2 and SN2 reactions, respectively, and the apparent n value is close to unity. When the concentration of water is low, decyl carbanions are probably protonated by dimethylformamide, little 1-decene and 1-decanol are produced, and the n value approaches two. © 1979, American Chemical Society. All rights reserved.