Anodic Oxidation of Alkyl Isocyanates and Their Thio Derivatives in Acetonitrile

Seven alkyl isocyanates (RNCO), five alkyl isothiocyanates (RNCS), and two aromatic cyanato derivatives (ArNCO) were electrochemically investigated by cyclic voltammetry and anodic controlled-potential electrolysis in acetonitrile at platinum anodes. It was found that RNCS compounds exhibited considerably lower anodic potentials than RNCO derivatives. The preparative electrochemical oxidation of RNCS was dependent on the nature of the alkyl group. Primary RNCS afforded mainly five-membered heterocyclic products while tertiary ones gave largely amides due to a-cleavage or isocyanates due to substitution of sulfur for oxygen processes. RNCO compounds were oxidized at the onset of the solvent electrolyte region and yielded amides and carbonyl products due to nucleophilic involvement of either acetonitrile or water, respectively, or formed products due to radical reactions (mono-, di-, and tricyanomethyl derivatives). ArNCO gave mostly polymeric products. Mechanistic routes for the formation of the various products are discussed.