Stoichiometric solvation effects. Part 3. Product–rate correlations for solvolyses of p-nitrophenyl chloroformate in alcohol–water mixtures

Abstract

Rate constants for solvolyses of p-nitrophenyl chloroformate in water, D₂O, CH₃OD, 50% D₂O–CH₃OD, and in aqueous binary mixtures of acetone, acetonitrile, ethanol and methanol are reported at 25 °C. Product selectivities are reported at 25 °C for a wide range of ethanol–water and methanol–water solvent compositions. Plots of first-order rate constants vs.Y_Cl (based on rates of solvolyses of 1-adamantyl chloride) give three separate curves for the aqueous mixtures with a small m value and unusual rate maxima for aqueous alcohol solvents. To account for these results, third-order rate constants k_ww and k_aa were calculated from the rate constants observed in pure solvents, together with k_aw and k_wa calculated from the intercept and slope of the plot of S vs. [water]/[alcohol] or via computer fitting. The calculated rate constants, k_calc and mol% of ester agree satisfactorily with the experimental values, supporting the stoichiometric solvation effect analysis. The kinetic solvent isotope effects determined in water and methanol are consistent with the proposed mechanism—a general base catalysed addition-elimination.