An electron spin resonance study of the second-order decay of 4-alkyl-2,6-di-t-butylphenoxyl radicals in solution

The decay of 4-methyl- and 4-ethyl-2,6-di-t-butylphenoxyl radicals in benzene solution is first-order at high radical concentrations and second-order at low radical concentrations. The concentration range in which the changeover from first- to second-order reaction occurs is determined by the equilibrium constant for quinol ether dimer formation from the phenoxyl radicals. Observed second-order rate constants at 22 °C for the loss of 4-methyl-, 4-ethyl-, and 4-isopropyl-2,6-di-t-butylphenoxyl radicals are, respectively, 2200, 500, and 2 I mol^–1 s^–1. The activation energy for the decay of 4-methyl-2,6-di-t-butylphenoxyl in benzene solution is 3·2 ± 0·3 kcal mol^–1.