SUBSTITUENT EFFECTS OF ALKYL GROUPS ON THE DECOMPOSITION OF TERT-ALKYL PEROXIDES

摘要

In order to clarify substituent effects of alkyl groups on the decomposition of various tert-alkyl peroxides (RCMe(2)OOR'), the decomposition of 1-methoxy-1-(tert-alkylperoxy)cyclohexanes 3 and 1,1-bis(tert-alkylperoxy)cyclohexanes 4 has been studied by use of methods of kinetics and product analysis in cumene with the range of temperatures from 80-110 degrees C and compared with those of the corresponding peroxyesters (1; R' = CO-t-Bu) and dialkyl peroxides (2; R' = t-Bu). The decomposition rates for each peroxide series decrease in the following order: 1 much greater than 3 much greater than 4 much greater than 2. The decomposition rate for the series of peroxides 1 decreases in the following order: R = t-BuCH(2) much greater than i-Pr much greater than Et > Pr > Me. But, for the series of peroxides 2, 3, and 4, R = t-BuCH(2) much greater than i-Pr much greater than Pr > Et much greater than Me. The decomposition rate is expressed by a modified Taft equation: log k(d) = rho*Sigma sigma(CH2R)* + nh + C, which contains both inductive and C-H hyperoconjugation effects of alkyl groups. On the basis of the isokinetic relationship of the activation parameters, the Taft equation, and the decomposition products, the decomposion mechanism via an polar activation complex having a slightly stretched C-alpha - C-beta bond neighboring to the peroxy oxygen atom is suggested and the abnormal behavior of neopentyl group is discussed. [References: 40]