The one electron reduction of primary alkyl iodides at palladiated surfaces. A convenient and general source of alkyl radicals

Abstract

Primary alkyl halides RI were reduced at smooth palladium electrodes (as well as palladiated copper, nickel, platinum and glassy carbon) in organic solvents such as dimethylformamide, propylene carbonate and acetonitrile in the presence of tetraalkylammonium salts. Under these experimental conditions all iodo derivatives exhibited a very large cathodic activation compared to the processes at more conventional materials like bare platinum and glassy carbon. The observed shifts towards less cathodic potentials were so large that in all cases the first reduction step turned to a diffusion one electron process. Thus under the given conditions, the cathodic reduction of RI’s occurred in two well separated one electron steps, suggesting therefore the formation of alkyl radicals as such. Microcoulometry at the level of the first step confirmed that the reaction is monoelectronic with a quantitative loss of iodide. The transient formation of free radicals is also supported by GC/MS results (presence of R–R and R(–H) type compounds after electrolysis). Finally ESR experiments confirm the transient formation of alkyl radicals which were trapped by nitrones.