Solvent and temperature effects on the rate constants of solvolysis of tert-butyl bromide in mono- and di-alcohols

Abstract

Rate constants, k, for the solvolytic reactions of 2-bromo-2-methylpropane (Bu^tBr) in the monoalcohols propan-1-ol and butan-1-ol and in the dialcohols ethane-1,2-diol, propane-1,3-diol and butane-1,4-diol are reported, at different temperatures. These values, the Arrhenius activation energies, E_a, and the thermodynamic functions of activation, Gibbs energy (Δ^‡G^⊖), enthalpy (Δ^‡H^⊖) and entropy (Δ^‡S^⊖) are interpreted and compared with previous results in methanol and ethanol. According to the Intersecting-state model, the reaction-energy profile is shaped and the solvent effect on the Gibbs energy of activation, Δ^‡G^⊖, is analysed.

At the molecular level, the dominant solvent–solute interactions are examined. The results show that changes in E_a. (or Δ^‡H^⊖) most affect the changes in the k values when dialcohols are used in place of monoalcohols; Δ^‡S^⊖ seems to control the differences in the k values within the set of monoalcohols.