Kinetic evaluation of the solvolysis of isobutyl chloro- and chlorothioformate esters

The specific rates of solvolysis of isobutyl chloroformate (1) are reported at 40.0 degrees C and those for isobutyl chlorothioformate (2) are reported at 25.0 degrees C, in a variety of pure and binary aqueous organic mixtures with wide ranging nucleophilicity and ionizing power. For 1, we also report the first- order rate constants determined at different temperatures in pure ethanol (EtOH), methanol (MeOH), 80% EtOH, and in both 97% and 70% 2,2,2- trifluoroethanol (TFE). The enthalpy (Delta H-not equal) and entropy (Delta S-not equal) of activation values obtained from Arrhenius plots for 1 in these five solvents are reported. The specific rates of solvolysis were analyzed using the extended Grunwald- Winstein equation. Results obtained from correlation analysis using this linear free energy relationship (LFER) reinforce our previous suggestion that side-by-side addition-elimination and ionization mechanisms operate, and the relative importance is dependent on the type of chloro- or chlorothioformate substrate and the solvent.