Kinetic study of the reactions of tert-butyl radicals in the liquid phase in the presence and absence of oxygen

Abstract

The photolyses of solutions of 2,2′-azoisobutane and 2,2,4,4-tetramethylpentan-3-one in decane in glass and metal cells, have been used to generate tert-butyl and, by reaction with oxygen, tert-butylperoxyl radicals. Time-dependent product yields from reactions in oxygenated and oxygen-free solutions have been measured over a range of temperatures (298–398 K). For each precursor, for a given set of conditions, the general features of the reactions are independent of the cell used, although the absolute rates of product formation are different. The major difference between the reactions of the two precursors lies in the initial photochemical step. For 2,2′-azoisobutane this leads directly to two tert-butyl radicals whereas the ketone gives a tert-butyl and a 2,2-dimethyl-propanoyl radical. The product distributions can be accounted for in terms of the reactions of these radicals within a solvent cage in competition with cage escape and subsequent reaction. A single kinetic model that accounts for the reactions of both precursors, in the presence or absence of oxygen, at the temperatures studied, is described.