The kinetics of disproportionation of the 2,6-di-t-butyl-4-methyl phenoxy radical

Abstract

The reaction between 2,6-di-t-butyl- p-cresol (BHT) and lead dioxide produces the 2,6-di-t-butyl-4-methyl phenoxy radical. Decay of this radical in THF and benzene has been studied by optical and ESR methods. Decay is second order with respect to the radical, with a specific rate constant k d = 3·33 × 10 2 M −1 sec −1 in THF and k d, = 4·59 × 10 2 M −1 sec −1 in benzene at 24·0 ± 1·0°. The speci rate constant is independent of [BHT] and [PbO 2], but is extremely sensitive to oxygen. Isolation of dimeric products 1,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)ethane and 3,3′, 5,5′-tetra-t-butyl-4,4′-stilbene-quinone and observation of the quinone methide intermediate in both solvent systems suggest that disproportionation of phenoxy radicals to yield quinone methide and the parent phenol is the mechanism for phenoxy decay.