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 been investigated by using the nitroxide radical-trapping technique. tert-Alkoxyl radicals generated from the thermolysis underwent the unimolecular reactions, beta-scission, and 1,5-H shift, competing with hydrogen abstraction from cumene. The absolute rate constants for beta-scission of tert-alkoxyl radicals, which vary over 4 orders of magnitude, indicate the vastly different behavior of alkoxyl radicals. However, the radical generation efficiencies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu(t)()), supporting a mechanism involving concerted two-bond scission within the solvent cage to generate the tert-butyl radical, CO(2), and an alkoxyl radical. The thermolysis 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)Sigmasigma - (0.31 +/- 0.04)SigmaE(s)(c), was obtained].
Nakamura
T
()()Fine Chemicals and Polymers Research Laboratory, NOF Corporation, 82 Nishimon, Taketoyo-cho, Chita-gun, Aichi 470-2398, Japan, Faculty of Science, Griffith University, Nathan, Queensland 4111, Australia, and CSIRO Molecular Science, Bag 10.
Busfield
WK
Jenkins
ID
Rizzardo
E
Thang
SH
Suyama
S