Reactions of some simple α- and β-hydroxyalkyl radicals with Cu2+ and Cu+ ions in aqueous solution

Using pulse radiolysis, rate constants have been measured for the reactions of the hydroxyalkyl radicals CH2OH, CH3CHOH, (CH3)2COH, CH2CH2OH and CH2C(CH3)2OH with Cusup(I) and Cusup(II) ions in aqueous solutions. For Cusup(II) the reaction was followed by observing the rate of formation of Cusup(I) which was measured as the Cusup(I)-acrylamide or Cusup(I)-ethylene complexes. For the reaction of the α-hydroxyalkyl radicals with Cusup(II), the rate constants decrease in the order primary > secondary > tertiary and have values of the order of 108 dm3 mol-1 s-1. These results are consistent with the reaction proceeding via organocopper complexes, but these complexes have not been directly observed. The β-radicals react more slowly than the α-radicals and ethylene oxide is produced in the oxidation of CH2CH2OH by Cu2+. Rate constants for the reaction of the α- and β-radicals with Cu+ are estimated to be approximately 1010 dm3 mol-1 s-1, and for the reaction of the β-radicals with the Cusup(I)-ethylene complex are estimated to be approximately 5 x 107 dm3 mol-1 s-1. Organocopper intermediates in the reactions with Cu+ have been observed spectrophotometrically and absorb in the region 350-550 nm. The β-radicals oxidise Cusup(I) to Cusup(II) and are themselves reduced to the corresponding olefin. The Cusup(I)-α-radical complexes decompose to Cu+ and the radical which then reduces the Cu2+ present. Mechanisms for these reactions are proposed. Rate constants have also been obtained for the addition of the radicals (not CH2CH2OH) to acrylamide (approximately 3 x 107 dm3 mol-1 s-1) and CH2CH2OH to ethylene (approximately 2 x 106 dm3 mol-1 s-1). (author)