Correlation of the Rates of Solvolysis of Isopropyl Fluoroformate Using the Extended Grunwald-Winstein Equation

Abstract

The specific rates of solvolysis of isopropyl fluoroformate are well correlated using the extended Grunwald-Winstein equation, with a sensitivity (1) to changes in solvent nucleophilicity (N-T) and a sensitivity (m) to changes in solvent ionizing power (Y-Cl). The sensitivities (l = 1.59 +/- 0.16 and m = 0.80 +/- 0.06) toward changes in solvent nucleophilicity and solvent ionizing power, and the k(F)/k(Cl), values are very similar to those for solvolyses of n-octyl fluoroformate, suggesting that the addition step of an addition-elimination mechanism is rate-determining. For methanolysis, a solvent deuterium isotope effect of 2.53 is compatible with the incorporation of general-base catalysis into the substitution process. The large negative values for the entropies of activation are consistent with the bimolecular nature of the proposed rate-determining step. These observations are also compared with those previously reported for the corresponding chloroformate and fluoroformate esters.