Electrochemical reactions of some organic free radicals at colloidal silver in aqueous solution

Abstract

Electron-transfer processes between simple 1-hydroxyalkyl, 1-ethoxyethyl, and 2-hydroxycyclohexadienyl radicals and metal ions at the surface of colloidal silver are described. C/sub 6/H/sub 6/OH radicals are oxidized by Ag/sup +/ to yield phenol. In the absence of Ag/sup +/, no electron exchange between C/sub 6/H/sub 6/OH and the silver particles takes place. When the silver particles carry a tiny deposit of thallium metal, the C/sub 6/H/sub 6/OH radicals are reduced. Cu/sup +/ (and Cu/sup 2 +/) ions adsorbed on the silver particles oxidize C/sub 6/H/sub 6/OH radicals. However, reduction of C/sub 6/H/sub 6/OH by Cu/sup +/ occurs, if the silver particles are covered with copper metal. 1-Hydroxyalkyl and 2-ethoxyethyl radicals reduce Tl/sup +/ ions in the presence of colloidal silver, but oxidize Tl atoms in homogeneous solution. Water can be decomposed to yield H/sub 2/ by 1-hydroxy-1-methyl and 1-hydroxyethyl, but not by 1-hydroxymethyl, 1-ethoxyethyl, and 2-hydroxycyclohexadienyl radicals. These findings are discussed in terms of standard potentials for the oxidation and reduction of the radicals and in terms of distributions of occupied and unoccupied electronic redox levels in the radicals and the colloidal metal. In these experiments ..gamma.. radiolysis was used to produce the radicals at a controlled rate.