On the Mechanism and Substituent Effects of the Tl(III) Oxidation of Phenylethylenes in Methanol

Abstract

The oxidation of phenylethylenes by Tl(NO3)3 in methanol proceeds rapidly and selectively to give the products resulting from the migration of aryl groups, i.e., (i) the 1,1-dimethoxy-2-phenylethanes from the corresponding styrenes, (ii) the phenylacetones from the α-methylstyrenes, and (iii) the two possible deoxybenzoines from the 1,1,-diphenylethylenes. The kinetic results, which indicate the formation of the thallic–organic intermediate to be the rate determining step, are discussed in terms of the mechanism of reaction and show the role of the coordination of Tl(III). Hammett's relationship, with ρ = −4.2, describes the substituent effects for the competitive oxidation of ring-substituted styrenes and α-methylstyrenes. The relative migratory aptitudes of aryl groups, as determined from the oxidation products of ring-substituted 1,1-diphenylethylenes, is correlated to Brown's σ+ constants, with ρ+ = −2.27.