Electron spin resonance studies of photo-oxidation by metal ions in rigid media at low temperatures. Part 2.—Ce(IV) photo-oxidation of carboxylic acids

Abstract

The primary processes in the photo-oxidation of a large number of carboxylic acids RCO₂H by Ce (IV) ions have been characterized by electron spin resonance spectroscopy, mostly at 77 K, utilizing an experimental procedure described previously. The most general pathway is that of oxidative decarboxylation to give the readily charactized R ˙, although alternative routes are found with lactic and acetic acids. Well-resolved spectra of R ˙ are recorded for R ˙= cyclopropyl, cyclobutyl, allyl, vinyl, ˙CH₂F, ˙CO₂H and ˙CH₂NH⁺₃, amongst others, and H ˙and D ˙ atoms display interaction with solvent protons. Secondary reactions are found in some cases, especially with two dicarboxylic acids which yield initially the spectra of ˙(CH₂)_nCO₂H(n= 1 or 2); these decay on warming, but renewed photolysis then produces either CH₃˙(from malonic acid) or C₂H₅˙(from succinic acid). Mechanisms of these processes are discussed.