Laser photolysis study of the reactions of alkoxyl radicals generated in the photosensitized decomposition of organic hyponitrites

Abstract

The triplet photosensitized decomposition of organic hyponitrites produces alkoxy radicals in good yields. For example, the quenching of p-methoxyacetophenone triplets by di-tert-butyl hyponitrite in benzene at 27 °C occurs with kq= 1.41 × 108M−1s−1, and ∼50% of the quenching events lead to a pair of tert-butoxy radicals. Steric effects play an important role in the kinetics of the quenching process; e.g., phenanthrene triplets are quenched 23 times faster by di-2-phenylethyl hyponitrite than by di-tert-butyl hyponitrite. The 2-phenylethoxy radicals undergo efficient β-cleavage to yield PhĊH2radicals with log (kβ/s−1) = 10.89 − 4830/θ, with θ = 2.3RT in cal/mol. The rate is markedly enhanced by polar solvents. The reaction of alkoxy radicals with diphenylmethanol is also sensitive to steric effects and occurs with rate constants (benzene, 27 °C) of 5.8 × 106and 2.6 × 107M−1s−1for tert-butoxy and 2-phenylethoxy radicals, respectively. © 1982, American Chemical Society. All rights reserved.