TRANSFER ENTHALPIES OF TERT-BUTYL CHLORIDE IN SOME AQUO-ORGANIC SOLVENTS

Transfer enthalpies, DELTAH(t)0, of tert-butyl chloride (t-BuCl) from water to aqueous mixtures of various cosolvents viz., protic ethanol ( EtOH), tert-butanol (t-BuOH), ethanediol (EG) and methoxyethanol (ME), aprotic 1,2-dimethoxyethane (DME) and 1,4-dioxane (D) and dipolar apr otic N,N-dimethylformamide (DMF) and dimethyl sulphoxide (DMSO), have been determined at 25-degrees-C by measuring the partial molal heats o f solution at infinite dilution (DELTAH(s)0)BAR with a rapid response Tronac (model 458) recording titration calorimeter by avoiding the unc ertainties from hydrolysis of t-BuCl in the solvents. These DELTAH(s)0 BAR values on extrapolation to zero cosolvent composition in each of t he aqueous cosolvent systems lead to a common value for that of water ((w)DELTAH(s)0BAR), which is equal to 6.27 +/- 0.25 kJ mol-1. DELTAH(t )0 values of the initial state (IS) of T-BuCl (= (s)DELTAH(s)0BAR-(w)D ELTAH(s)0BAR) on subtraction from the corresponding transfer activatio n energies partial derivative DELTAH(not-equal) (= (s)DELTA(not-equal) - (w)DELTAH(double dagger)) as obtained from parallel kinetic studies of the hydrolysis/solvolysis of t-BuCl in the solvents at different t emperatures, and reported elsewhere, helped determine the transfer ent halpies DELTAH(t)0(TS) of the transition state (TS). A comparative vie w of the composition profiles of DELTAH(s)0BAR, as well as of partial derivative DELTAH(not-equal) and DELTAH(t)0 (TS) in the solvent system s reflects that while the variations in DELTAH(t)0BAR values are guide d by complex structural and interaction effects in the respective solv ents, DELTAH(t)0 (IS) values are fairly small as compared to partial-d erivative DELTAH(not-equal) values. Evidently, partial-derivative DELT AH(not-equal) values are guided by the contributions of DELTAH(t)0 of TS rather than that of IS, contrary to what has been concluded by Arne tt et al. from the corresponding studies only in aqueous ethanol syste m.