Thermodynamics of proton transfer processes involving ammonium and some substituted ammonium ions in ethylene glycol

Abstract

An electromotive force method has been employed to determine the acidic dissociation constants of ammonium and several alkylammonium ions in ethylene glycol at nine temperatures from 5 to 45 °C, by use of cells of the type: Pt; H₂(gas 1 atm), BH⁺Br^–(m₁), B(m₂) ethylene glycol; AgBr–Ag, where B is the amine base. The change of the dissociation constant with temperature has been used to calculate the changes of entropy, enthalpy, and heat capacity associated with the corresponding dissociation process in the standard state. Comparison with the reported data for aqueous solution reveals that, besides the inductive effect of the substituents the solvophilicity of substituents towards glycol plays a predominant role in the overall process leading to the order of acid strengths of the methyl-, ethyl-, and hydroxyethyl-substituted ammonium ions in ethylene glycol as primary < secondary < tertiary.