Free energies and entropies of transfer of hydrogen halides from water to aqueous solutions of tetrahydrofuran, dioxane, and 1,2-dimethoxyethane and the structuredness of the solvents

Abstract

JAYATI DATTA and KIRON K. KUUDU. Can. J. Chem. 59. 3149 (1981). Standard free energies (AG,O) and entropies (AS:) of transfer of hydrogen iodide from water to some aqueous solutions of tetrahydrofuran (THF), dioxane (D), and 1,2-dimethoxyethane (DME) have been determined by measuring the emf's of the cell: Pt. H, (g, 1 atm);KOH (in,), KI (in,). solventAgI, Ag at seven equidistant temperatures ranging from 5 to 3YC. In each of these ethereal solvent systems AG,O values of HI, as well as of HCI and HBr obtained from the literature, and particularly of the individual ions, suggest that while H+ is increasingly stabilized, halide ions are increasingly destabilized due to the influence of cosolvent-induced larger "basicity" and smaller "acidity" of the mixed solvents compared to that of water, and both conformed to the expected order: D < THF < DME. Moreover, the relative order: C1-> Br-> I-in all the solvent systems is ascribable to the combined effects of "acid-base" and "soft-soft" interactions and the superimposed quadrupolar interactions in the case of D and the charge transfer to solvent (CTTS) complexation effect, especially on I in the case of THF. Analysis of the entropic contributions, TAStO, and particularly of the relative order of A Y (= TASto (H') + TASP,, (X-))for X = CI, Br. and I, in the light of the semi-quantitative theory proposed earlier by Kundu e t a / . . reveals that at initial compositions, while T H F promotes 3D structures of water. both D and DME break down the same; at higher compositions all the cosolvents disrupt the structure as usual due to packing imbalance. The nature and relative positions of AY-composition profiles also suggest that while increase of hydrophobic groups of the cosolvents increases the stabilization, increase in hydrophilicity or H-bonding sites decreases the stabilization of the 3D structure of water.

Enthalpies and Entropies of Transfer of Electrolytes and Ions from Water to Mixed Aqueous Organic Solvents

“…At even higher cosolvent concentrations the discrepancies become too large for the averages to be meaningful. For HBr, three mainly potentiometric studies have been reported. ,,, However, the results are in such poor agreement that no critical evaluation can be made. A similar situation exists for HI (Table ).…”

Kinetic solvent effects on acid-catalyzed hydrolysis of sucrose in aqueous mixtures of some protic, aprotic, and dipolar aprotic solvents

“…In fact AG(H+) has a downward trend at initial compositions because of the increased basicity of D + H 2 0 mixtures resulting from larger protophilicity of two basic 0-centres of dioxane molecules (21). But, as explained earlier (12), because of the possible shifting of the equilibria between the aquo-complexes of "boat" and "chair" forms of dioxane molecules with increased proportion of D, the basicity decreases at higher compositions.…”

Transfer thermodynamics of p-nitroaniline in aqueous solutions of some ionic and non-ionic cosolvents and the structuredness of the solvents

“…Strikingly enough, the relative positions of these profiles in D + water and DME + water mixtures get reversed and hence suggest that DME is a more effective structure breaker than D, as is expected from intrinsic and structural features of the cosolvent molecules. The observed initial inverse behaviour of these profiles, however, is possibly the Born-type electrostatic effect on the zwitterionic form of p N A , for at this region dielectric constant effects of DME + water nlixtures are inverse that of D + water mixtures (18).…”

“…18, 3 1) including our recently observed TAS;(HX) (18) or transfer entropies of ionization of water TS(AS') and TAS;(H~O) derived thereof (31), in D + water and DME + water mixtures have indicated that unlike IPA, D and DME induce 3D structure breaking right from the initial compositions. Moreover, the relative positions of these profiles in D + water and DME + water mixtures are also at variance with those for AY,(HX) [=As;(H') + AS;,,(X-)I where AS:,, is the non-Born or chemical contribution (l8), and also with the expected relative structure-breaking effect of these cosolvents, which is larger in DME than D. These observations substantiate our earlier contention derived from HBz (10) as a probe that there is a missing point in our semi-quantitative treatment for the larger-sized amphiphilic solutes like HBz (8) or pNA (9).…”

“…Aqueous solutions of others like D and DME and poly-01s like PG and GL are similar. The latter two cosolvent systems are particularly relevant since the results of these two solvents with graded increase of hydrophilic group from mono-01 IPA to di-01 PG and thence to tri-ol GL are likely to substantiate the earlier (10,17,18) contention that an increase in hydrophilicity or H-bonding sites of cosolvents decreases the stabilization of 3D structures of water.…”