STOICHIOMETRIC SOLVATION EFFECTS - PART 3 - PRODUCT-RATE CORRELATIONSFOR SOLVOLYSES OF P-NITROPHENYL CHLOROFORMATE IN ALCOHOL-WATER MIXTURES

Rate constants for solvolyses of p-nitrophenyl chloroformate in water, D2O, CH3OD, 50% D2O-CH3OD3 and in aqueous binary mixtures of acetone, acetonitrile, ethanol and methanol are reported at 25 degrees C, Prod uct selectivities are reported at 25 degrees C for a wide range of eth anol-water and methanol-water solvent compositions. Plots of first-ord er rate constants vs. Y-Cl (based on rates of solvolyses of 1-adamanty l chloride) give three separate curves for the aqueous mixtures with a small m value and unusual rate maxima for aqueous alcohol solvents. T o account for these results, third-order rate constants k(ww) and k(aa ) were calculated from the rate constants observed in pure solvents, t ogether with k(aw) and k(wa) calculated from the intercept and slope o f the plot of S vs. [water]/[alcohol] or via computer fitting, The cal culated 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 wa ter and methanol are consistent with the proposed mechanism-a general base catalysed addition-elimination.