HIGH PRESSURE STUDIES .4. CAGE EFFECTS AND ACTIVATION VOLUMES FOR HOMOLYTIC SCISSION REACTIONS

The effects of pressure on the rates of solution phase decomposition of the t-butyl peresters of phenylacetic acid, cyclohexanecarboxylic acid, and benzoic acid have been determined, as well as the pressure dependence of the product distributions of the first two peresters. In cumene at 79.6°, the observed activation volumes are t-butyl perbenzoate, +10 cc/mole; carbo-t-butylperoxycyclohexane, +3.9 cc/mole; and t-butyl phenylperacetate, + 1 to +3 cc/mole. The data are used to demonstrate that observed activation volumes are abnormally high for homolytic scission reactions in which cage recombination of the primary radical products can occur to regenerate starting material. Product data support the mechanistic proposals and additionally permit calculations of crude values for the difference in activation volumes for radical combination, disproportionation, and diffusion. © 1969, American Chemical Society. All rights reserved.