Substituent Effects of Alkyl Groups on the Decomposition of tert-Alkyl Peroxides

Article abstract of DOI:10.1021/jo00122a035

In order to clarify substituent effects of alkyl groups on the decomposition of various tert-alkyl peroxides (RCMe2OOR'), 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 deg 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 >> 3 > 4 >> 2.The decomposition rate for the series of peroxides 1 decreases in the following order: R = t-BuCH2 >> i-Pr >> Et > Pr > Me.But, for the series of peroxides 2, 3, and 4, R = t-BuCH2 >> i-Pr >> Pr > Et >> Me.The decompositon rate is expressed by a modified Taft equation : log k_d = ρ^*Σρ_CH2R^* + nh + C, which contains both inductive and C-H hyperconjugation effects of alkyl groups.On the basis of the isokinetic relationship of the activation parameters, the Taft equation, and the decomposition products, the decomposition mechanism via an polar activation complex having a slightly stretched C_α - C_β bond neighboring to the peroxy oxygen atom is suggested and the abnormal behavior of neopentyl group is discussed.