TRANSFER FREE-ENERGIES OF TRIMETHYLAMMONIUM HYDROCHLORIDE-A PRECURSORTO A POTENTIAL MODEL TRANSITION-STATE FOR SN1-TYPE HYDROLYSIS OF TERT-BUTYL CHLORIDE IN SOME AQUO-ORGANIC SOLVENTS

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 bee n determined in aqueous mixtures of various organic cosolvents viz pro tic tert-butanol (t-BuOH), ethylene glycol (EG), glycerol (GL) and met hoxyethanol (ME), aprotic dimethoxyethane (DMSO) and dioxane (D) and d ipolar aprotic 1,2-dimethylformamide (DMF) and dimethyl sulphoxide (DM SO). These have been determined by measuring the solubilities of spari ngly soluble salt Me3NHBPh, (Ph=phenyl) at 25-degrees-C in the solvent s and by using the relation: DELTAG(t)0 (Me3NHCl) = DELTAG(T)0(Me3NHBP h4) - DELTA G(t)0 (Ph4B-) + DELTAG(t)0 (CI-). The required individual ion contributions for the solvents, based on widely used Ph4AsPh4B (TB TB) reference electrolyte (RE) assumption, have been taken from previo us studies. The chemical contributions of DELTAG(t)0(i) values of Me3N H+ and Cl- have been obtained after subtracting the respective contrib utions of cavity, Born and ion-dipole interactions, as computed by sca led particle theory (SPT), Born and Buckingham formulations respective ly 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 h ydrophilic hydration (H1H) effect arising chiefly from the relative pr oticity/aproticity of the respective cosolvents, DELTAG(t,HbH)0 H(Me3N H+) values are guided by hydrophobic hydration (H(b)H) effect arising chiefly from the hydrophobic propensity of Me3NH+, apart from the disp ersion, relative basicity and structural interaction effect of the cos olvents.