Transfer free energies, DELTAG(t)0, of trimethylammonium hydrochloride (Me3NHCl)-a precursor to a potential model for the transition state (TS) for S(N)1-type hydrolysis of tert-butylchloride (t-BuCl), have been determined in aqueous mixtures of various organic cosolvents viz protic tert-butanol (t-BuOH), ethylene glycol (EG), glycerol (GL) and methoxyethanol (ME), aprotic dimethoxyethane (DMSO) and dioxane (D) and dipolar aprotic 1,2-dimethylformamide (DMF) and dimethyl sulphoxide (DMSO). These have been determined by measuring the solubilities of sparingly soluble salt Me3NHBPh, (Ph=phenyl) at 25-degrees-C in the solvents and by using the relation: DELTAG(t)0 (Me3NHCl) = DELTAG(T)0(Me3NHBPh4) - DELTA G(t)0 (Ph4B-) + DELTAG(t)0 (CI-).
The required individual ion contributions for the solvents, based on widely used Ph4AsPh4B (TBTB) reference electrolyte (RE) assumption, have been taken from previous studies. The chemical contributions of DELTAG(t)0(i) values of Me3NH+ and Cl- have been obtained after subtracting the respective contributions of cavity, Born and ion-dipole interactions, as computed by scaled particle theory (SPT), Born and Buckingham formulations respectively and are referred to as DELTAG(T,H1H)0(Cl-) and DELTAG(t,HbH)0(Me3NH+).
This is because while DELTAG(t,H.1H)0(Cl-1) values are guided by hydrophilic hydration (H1H) effect arising chiefly from the relative proticity/aproticity of the respective cosolvents, DELTAG(t,HbH)0 H(Me3NH+) values are guided by hydrophobic hydration (H(b)H) effect arising chiefly from the hydrophobic propensity of Me3NH+, apart from the dispersion, relative basicity and structural interaction effect of the cosolvents.