Evidence for the formation of thermally unstable dialkyl trioxide molecules using electron spin resonance spectroscopy

Abstract

U.v. photolysis of solutions of di-t-butyl peroxide in oxygenated cyclopropane or dichlorodifluoromethane at low temperatures (ca. 140 K and below) produces no detectable concentration of free radicals. On cessation of photolysis a single-line e.s.r. spectrum assigned to the t-butylperoxyl radical begins to appear and reaches a steady intensity within a few minutes. The e.s.r. signal is destroyed immediately upon resuming the photlysis and the cycle can be repeated several times. These observations are explained by the formation of the primary–tertiary dialkyl trioxide, MeOOOBu^t, which is thermally unstable even at 140 K. One of the possible modes of scission of the dialkyl trioxide generates the t-butylperoxyl radical, which is stable at these temperatures in the absence of photolysis. It is shown that dialkyl trioxides can also be formed at low temperatures in more reactive solvents, e.g. toluene, and that their presence may lead to erroneous measurements of free-radical kinetics.