Electron spin resonance studies of photo-oxidation by metal ions in rigid media at low temperatures. Part 3.—Ce(IV) photo-oxidations of aldehydes, ketones, esters and amides

Abstract

A survey is presented of the primary processes in the photo-oxidation by Ce(IV) ions at 77 K of a variety of organic molecules classified by functional group; these processes have been determined by characterization of the resulting organic free radical by electron spin resonance spectroscopy. Aldehydes RCHO and aldehyde hydrates RCH(OH)₂ are oxidized to RĊO and RĊC(OH)₂ respectively, although C₂H₅ĊO disappears at 120 K, producing instead CH₃ĊHCHO. Ketones produce either the alkyl radical R from RCOR′ or the radical derived by abstraction of a hydrogen atom from the methylene or methine groups adjacent to the carbonyl group; in some cases both types of radical are discernible. Esters also undergo C—H or C—C fission processes depending on the degree of substitution of the R fragment of RCO₂R′, whilst formamide yields a spectrum of ·CONH₂. Methyl methacrylate yields a vinylic monomer radical at 77 K which induces polymerization at 175 K to give the polymethyl methacrylate radical.