Kinetics of the decomposition of 1-aryl-2,2,2-trihalogenoethanols in aqueous base

Abstract

The decomposition of several 1-aryl-2,2,2-trichloro- and 1-aryl-2,2,2-tribromo-ethanols in aqueous base is studied. The title compounds yield the corresponding benzaldehydes and the halogenoform with base. The kinetics are compatible with an (E1cB)_R mechanism. Values for the rates of collapse of the intermediate alkoxides and for the pK_a values of all ethanols are estimated. Electron-donating substituents on the ring facilitate decomposition and decrease the acidity of the ethanols. Solvent isotope effects, k_H2O/k_D2O′ for the reactions are small. The absence of mandelic acid derivatives among the products, in apparent disagreement with other related studies, is discussed and justified in the light of a scheme which reconciles previous conflicting observations found in the literature.