Photo-induced decomposition of organic peroxides: Ultrafast formation and decarboxylation of carbonyloxy radicalsw

Recent experimental and theoretical studies shed new light on the ultrafast photochemical decomposition of organic peroxides, R1C(O)O–OR2. This reaction both is of fundamental interest, directed toward a detailed understanding of unimolecular processes, and of practical relevance because of the widespread use of peroxides as initiators in free-radical polymerization. An overview is given on picoand femtosecond UV pump-VIS/near IR/IR probe experiments on the decomposition of diaroyl peroxides (R1 1⁄4 aryl, R2 1⁄4 C(O)–R1), of tert-butyl peroxyesters (R1 1⁄4 aryl or benzyl, R2 1⁄4 tert-butyl), and of tert-butyl peroxycarbonates (R1 1⁄4 aryloxy, R2 1⁄4 tert-butyl). Analysis of the time-resolved concentration profiles is carried out in conjunction with quantumchemical calculations, in particular on the structure and reactivity of the intermediate carbonyloxy radicals, R1–CO2. A semi-quantitative model is presented which allows for an adequate understanding of the ultrafast processes subsequent to instantaneous peroxide photodissociation.