One-Bond Azo Initiators. Thermal Decomposition of Substituted (Phenylazo)triphenylmethanes

Article abstract of DOI:10.1021/ja00350a040

Rate constants for thermal decomposition of the p-NO2, m-NO2, m-methyl, p-methyl, and unsubstituted (phenylazo)triphenylmethane (1) in octane and several aromatic solvents have been determined and correlated with medium viscosity.Decomposition rate constants for p-NO2 and unsubstituted 1 in n-alkane solvents previously reported have been reanalyzed.These data indicate that β scission of intermediate diazenyl radicals is an important process in n-alkane solvents and becomes more important as increasing viscosity retards separative diffusion.However, β scission is not an important process in the aromatic solvents.Pressure severely retards the decomposition rates of p-NO2 and unsubstituted 1 in octane, cumene, and tert-butylbenzene, giving activation volumes of +16 to +21 cm³/mol.Comparison of these pressure data with atmospheric pressure data gives activation volumes for formation and recombination of diazenyl radical-triphenylmethyl radical pairs.Problems associated with Hammett correlations of decomposition rates of the variously substituted compounds 1 are discussed.