Experimental and Theoretical Investigations of the Ultrafast Photoinduced Decomposition of Organic Peroxides in Solution: Formation and Decarboxylation of Benzoyloxy Radicals

Abstract

The light-induced (266 nm) ultrafast decarboxylation of two peroxides R1−C(O)O−OR2, with R1 = phenyl and R2 = benzoyl or tert-butyl, in solution has been studied on the picosecond time scale by absorption spectroscopy with a time resolution typically of 100 to 200 fs. The reaction was investigated in various solvents of different polarity and viscosity to elucidate the influence of the solvent environment on the decarboxylation rate. Transient intermediate benzoyloxy radicals, R1−CO2, were monitored at wavelengths between 300 and 1000 nm. While the primary dissociation of the peroxide is too fast to be resolved, the dissociation of intermediate benzoyloxy radicals is clearly detected on the picosecond time scale. The mechanism of light-induced two-step dissociation is discussed, as is the dependence of reaction dynamics on the type of substituent R2 as well as the branching ratio between prompt and delayed CO2 formation. A model for the decarboxylation process is presented that is based on molecular struc...