The Grunwald-Winstein Relationship in the Solvolysis of β-Substituted Chloroformate Ester Derivatives: The Solvolysis of 2-Phenylethyl and 2,2-Diphenylethyl Chloroformates

摘要

Solvolysis rate constants of 2-phenylethyl-(2-PhCH2CH2OCOCl, 1) and 2,2-diphenylethyl chloroformate (2,2-Ph2CHCH2OCOCl, 2), together with the previously studied solvolyses of a- and β-substituted chloroformate ester derivatives, are reported in pure and binary solvents at 40.0 °C. The linear free energy relationship (LFER) and sensitivities (l and m) to changes in solvent nucleophilicity (N_t) and solvent ionizing power (Y_(Cl)) of the solvolytic reactions are analyzed using the Grunwald-Winstein equation. The kinetic solvent isotope effects (KSIEs) in methanol and activation parameter values in various solvents are investigated for 1 and 2. These results support well the bimolecular pathway with same aspects. Furthermore, the small negative values of the entropies of activation of solvolysis of 1 and 2 in the highly ionizing aqueous fluoroalcohols are consistent with the ionization character of the rate-determining step, and the KSIE values of 1.78 and 2.10 in methanol-d indicate that one molecule of solvent acts as a nucleophile and the other acts as a general-base catalyst. It is found that the β-substituents in alkyl chloroformate are not the important factor to decide the solvolysis reaction pathway.