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

1998; Royal Society of Chemistry; Issue: 5 Linguagem: Inglês

10.1039/a800179k

2050-8239

In Sun Koo, Kiyull Yang, Keumduck Kang, Ikchoon Lee, T. WilliamBentley,

Pharmaceutical and Antibiotic Environmental Impacts

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.YCl (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 kww and kaa were calculated from the rate constants observed in pure solvents, together with kaw and kwa calculated from the intercept and slope of the plot of S vs. [water]/[alcohol] or via computer fitting. The calculated rate constants, kcalc 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.