Solvent Effects on the Rates of Decomposition of Bis(1-methyl-1-phenylethyl) Peroxide

Abstract

In spite of the efforts of many investigators, the solvent effects on the rates of unimolecular decompositions for a wide variety of peroxides and azo compounds are still not evaluated enough. This paper describes the effects of monosubstituted benzenes(I) and normal alkanes 00 on the rates of thermal decomposition of“dicumyl peroxide”(bis(1-methyl-1-phenylethyl)peroxide) (DCP) at 120∼140°C and also those of (II) on, the rates of photodecomposition at 25°C.
The both decomposition rates of DCP in these solvents were the first order over the range of the concentrations from 10^-3 to 10^-2 molii. The rate constants (k_d) changed in these solvents. The k_d in benzonitrile was greater than that in tetradecane by a facto r of 3.2 at 120°. In (I), k_d was related to the dielectric constant, and/or E_T valu e of each solvent and the activation entropy obtained decreased as the polarity of solvent i n creased. In (II), the straight line with a positive slope was shown between k_d and th e reciprocal of viscosity and was also observed by the use of the Pryor's equation on viscos i ty dependence. However, the k_d in (I) was independent of the solvent viscosity. On the basis of these results, it has been found that the rates of decomposition of DCP in (I)increase with an increase in the solvent polarity, while those in nonpolar solvent (II) decreas e with an increase in the solvent viscosity.
The Pryor's equation and a v a lue in it were examined. The equation with 1/2 of a could be applied to (II) regardless of different decomposition temperatures, but the application to (I) remains obscure as the a value was undecided yet.