Thermal decomposition mechanisms of tert-alkyl peroxypivalates studied by the nitroxide radical trapping technique

The thermolysis of a series of tert-alkyl peroxypivalates 1 in cumene has b een investigated by using the nitroxide radical-trapping technique. tert-Al koxyl radicals generated from the thermolysis underwent the unimolecular re actions, beta-scission, and 1,5-H shift, competing with hydrogen abstractio n from cumene. The absolute rate constants for beta-scission of tert-alkoxy l radicals, which vary over 4 orders of magnitude, indicate the vastly diff erent behavior of alkoxyl radicals. However, the radical generation efficie ncies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu-t), suppor ting a mechanism involving concerted two-bond scission within the solvent c age to generate the tert-butyl radical, CO2, and an alkoxyl radical. The th ermolysis rate constants of tert-alkyl peroxypivalates 1 were influenced by both inductive and steric effects [Taft-Ingold equation, log-(rel k(d)) = (0.97 +/- 0.14)Sigma sigma* - (0.31 +/- 0.04)Sigma E-s(c), was obtained].