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

초록

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 α- and β-substituted chloroformate ester derivatives, are reported in pure and binary solvents at 40.0 oC. The linear free energy relationship (LFER) and sensitivities (l and m) to changes in solvent nucleophilicity (NT) and solvent ionizing power (YCl) 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.

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