| Abstract
| - Reactivities of methyl radical and carbene species, electrogenerated on the surfaces of group IB metalsvia reductive cleavage of simple methyl and methylene halides (bromides and iodides) in aqueous solution,are investigated using cyclic voltammetry associated with the products' identification by gas chromatography/mass spectrometry. To appreciate specific changes in the electrochemical behavior of the above halides,related to the nature of the electrode material, similar measurements have also been carried out employingan inert glassy carbon electrode. The replacement of glassy carbon by the group IB metals Ag and Cu wasfound to lead to a sensible shift (several hundred mV) in their reduction potentials (Ep). Consequently,the reduction of CH2Br2, CH2I2, and CH3I starts at potentials positive with respect to the potentials of zerocharge (pzc) of Ag and Cu, producing significant amounts of ethylene and ethane, respectively. Methanebecomes the dominant reaction product only at the potentials more negative than Ep. The extent of interactionbetween the reaction intermediates and the electrode surface clearly depends not only on the potentialbut also on the electronic structure of the electrode. This was confirmed by the results of experimentsconducted using the Au and glassy carbon electrodes, having pzc values much more positive than Ag andCu, at which methane was the only detected product of the CH3X and CH2X2 reduction, over the entirerange of potentials. The collected results demonstrate that the reactions undergone by the electrogeneratedCH2 and •CH3 species can be oriented toward formation of either ethylene/ethane or methane by a suitablechoice of the electrode material and of the range of applied potentials. The use in this study of Ag and Cuelectrodes allows generation of the CH2 and •CH3 radicals above the onset potential for H2 evolution, sothat their reactivity can be investigated virtually in the absence of competing reactions.
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