Inter- and intra-molecular catalysis in the enolization of derivatives of 2′-carboxyacetophenone

Abstract

Kinetic results are reported for the rates of enolization of ten derivatives of 2′-carboxyacetophenone, as measured by their rates of iodinalion or detritiation. Rates of intramolecular proton transfer in the anions of these compounds can be measured throughout, as well as transfer to hydroxide ions, and in some instances intermolecular catalysis by added pyridine or acetate ions can also be detected. The efficiency of the intramolecular process is considerably affected by substituents, and the major effects appear to be steric ones. The equilibrium proportion of cyclic lactol isomer in aqueous solutions of these compounds was determined by combining conventional pK values with the catalytic effect of their anions in the decomposition of nitramide, and there is an inverse relation between the proportion of cyclic isomer and the efficiency of the intramolecular proton transfer. Kinetic isotope effects are reported for several intra- and inter-molecular processes, and these also are sensitive to geometrical factors.