Determination of absolute transfer free energies of hydroxyl ion from water to aqueous 2-methoxy ethanol

1981 ◽  
Vol 59 (7) ◽  
pp. 1153-1159 ◽  
Author(s):  
Abhijit Bhattacharya ◽  
Asim K. Das ◽  
Kiron K. Kundu
Keyword(s):  
Ethylene Glycol ◽  
Mixed Solvents ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Free Energies Of Transfer ◽  
Hydroxyl Ion ◽  
Relative Stabilization ◽  
Solvent Systems ◽  
Reference Electrolyte

Absolute standard free energies of transfer ΔGt0 of OH− from water to aqueous mixtures of 2-methoxy ethanol (ME) have been evaluated at 298.15 K by combining the apparent transfer free energies of the lyate ion that were obtained from the standard emf's of the double cell:[Formula: see text]and that from the autoionization constants of these mixed solvents determined by use of the cell comprising H2– and Ag–AgCl electrodes. The required ΔGt0 values of K+ and H+ were determined earlier using the well-known tetraphenyl arsonium tetraphenyl boride (TATB) reference electrolyte method. These values and their non-Born type contributions in particular, are found to be increasingly positive in water-rich compositions, indicating that the relative stabilization of OH− and the acidity of the mixed solvents decrease with increasing cosolvent composition. These, when compared with those in aqueous mixtures of ethylene glycol and 1,2-dimethoxy ethane, are found to lie intermediate between the latter solvent systems conforming to what is expected from the structural and electronic features of the cosolvents.

Ionization of ethylene glycol in isodielectric acetonitrile + ethylene glycol mixtures at 25 °C

1979 ◽  
Vol 57 (18) ◽  
pp. 2470-2475 ◽  
Author(s):  
Kumardev Bose ◽  
Kiron K. Kundu
Keyword(s):  
Free Energy ◽  
Ethylene Glycol ◽  
Mixed Solvents ◽  
Solvent Composition ◽  
Free Energies ◽  
Emf Measurements ◽  
Free Energies Of Transfer ◽  
Mixed Systems

The autoprotolysis constants (Ksm) of ethylene glycol in isodielectric acetonitrile + ethylene glycol mixtures have been determined at 25 °C from emf measurements on the cell[Formula: see text]From these values, those of δΔG0, the free energy of ionization of ethylene glycol in these mixed solvents relative to that in pure glycol, have been computed. The nature of variation of δΔG0 with solvent composition has been compared with that in two other mixed systems: water + ethylene glycol and methanol + 1,2-propanediol and the intrinsic differences between the solvation characteristics of the various solvents have been pointed out. The standard free energies of transfer of the glycoxide ion, ΔGt0(OEg−), from pure glycol to acetonitrile + glycol mixtures have also been estimated using ΔGt0(H+) values obtained earlier. The glycoxide ion is increasingly desolvated as the acetonitrile content of the solvent increases, as indicated by increasingly positive values of ΔGt0(OEg−). This behaviour has been compared with those of ΔGt0(H+) and ΔGt0(Cl−) determined previously.

Free energies of transfer of some single ions from ethylene glycol to its isodielectric mixtures with acetonitrile at 25 °C

1979 ◽  
Vol 57 (18) ◽  
pp. 2476-2481 ◽  
Author(s):  
Kumardev Bose ◽  
Kiron K. Kundu
Keyword(s):  
Ethylene Glycol ◽  
Aprotic Solvent ◽  
Ion Solvation ◽  
Free Energies ◽  
Solvent Interactions ◽  
Free Energies Of Transfer ◽  
Isodielectric Mixtures ◽  
The Individual ◽  
Reference Electrolyte ◽  
Electrolyte Ph

Free energies of transfer (ΔGt0) of the reference electrolyte Ph4AsBPh4 (Ph = phenyl) from ethylene glycol to its approximately isodielectric mixtures with acetonitrile have been determined at 25 °C from the measurement of the solubilities of KPi, Ph4AsPi, and KBPh (Pi = picrate) in these solvents. Using the assumption [Formula: see text] values for the individual ions K+, Pi−, Ph4As+, and Ph4 s− have been estimated. These, in conjunction with previously determined values of ΔGt0 for MCl (M = Li, Na, K, Rb, Cs, and H), KBr and KI have provided ΔGt0 values for Cl−, Br−, I−, and M+ ions. Ionic ΔGt0's have been interpreted in terms of specific ion–solvent interactions. The contrasting behaviour of ethylene glycol and acetonitrile in ion-solvation is shown to be characteristic of the protic and dipolar aprotic solvent types respectively.

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

1986 ◽  
Vol 64 (8) ◽  
pp. 1638-1642 ◽  
Author(s):  
Urmila Mandal ◽  
Kaushik Das ◽  
Kiron Kumar Kundu
Keyword(s):  
Transition State ◽  
Optical Rotation ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Initial State ◽  
Composition Profiles ◽  
Acid Catalyzed ◽  
Solvent Systems ◽  
Hydrolysis Of ◽  
Reference Electrolyte

Rate constants of acid-catalyzed hydrolysis of sucrose (S) to D-glucose and L-fructose have been determined at 25 °C by optical rotation measurements in aqueous mixtures of protophobic protic glycerol (GL), protophilic protic urea (UH), aprotic dioxane (D), and dipolar aprotic dimethyl sulphoxide (DMSO). Transfer free energies of the substrate sucrose, [Formula: see text] have also been determined in the solvents from solubility measurements. These values as well as those of H+, as obtained earlier by use of the widely used tetraphenylarsonium tetraphenylboron (TATB) reference electrolyte assumption, yielded transfer free energies of the transition state. The observed log (ks/kw) – composition profiles reveal that the rates increase monotonically in GL–water mixtures, that decrease more or less monotonically in UH– and DMSO–water mixtures, and decrease up to 10 mol% D in D–water mixtures, beyond which the values tend to increase. Examination of [Formula: see text]–composition profiles for the different species in each case indicates that the initial and transition state solvation get more or less compensated and the observed rates are dictated by the increased solvation of H+ in aqueous UH, DMSO, and D co-solvent systems. But in GL–water mixtures the decreased solvation of the transition state compared with the initial state is overcome by the decreased solvation of H+, thus resulting in the gradual enhancement of the rates of the reaction. The observed linearity of the correlative plots of −δ(ΔG≠) [= RT ln (ks/kw)] vs. [Formula: see text] with distinctly different slopes in the two cases also substantiates the relative importance of H+ solvation in dictating the rates of the reaction in these widely different aqueous co-solvents.

Thermodynamics of autoionization of 2-methoxy ethanol + water mixtures and structuredness of the solvents

1985 ◽  
Vol 63 (4) ◽  
pp. 804-808 ◽  
Author(s):  
Prabir K. Guha ◽  
Kiron K. Kundu
Keyword(s):  
Dielectric Constant ◽  
Ethylene Glycol ◽  
Structural Changes ◽  
Mixed Solvents ◽  
Three Dimensional ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Acid Base ◽  
Emf Measurements ◽  
Structure Breaking

Standard free energies (ΔG0) and entropies (ΔS0) of autoionization of aqueous mixtures of 10, 30, 50, and 70 wt.% of 2-methoxy ethanol (ME) have been evaluated from the autoionization constants (Ks) of the solvents as determined from emf measurements of the cell Pt, H2 (g, 1 atm)/KOH (m1), KBr (m2), solvent/AgBr–Ag at seven equidistant temperatures ranging from 15 to 45 °C. The observed increase in pKs and the related δ(ΔG0) (= sΔG0 − wΔG0) has been ascribed to be the effect of decreased dielectric constant, increased basicity and decreased acidity of the mixed solvents compared to that of water. Analysis of relative entropic contributions of autoionization, Tδ(ΔS0) (= T(sΔS0 − wΔS0)) and their chemical part, Tδ(ΔS0)ch in the aqueous mixtures of ME as well as the closely related cosolvents like ethylene glycol (EG) and 1,2-dimethoxy ethane (DME), appears to suggest that unlike EG but like DME, ME has an overall structure breaking propensity of three dimensional (3D) tetrahedral structures of water. But the transfer entropies of water ΔSt0(H2O) derived thereof, for these cosolvents suggest that while the structural changes induced by protic EG are seemingly obseured due to the involved multiple acid-base equilibria with water, and that by aprotic DME are disturbed by the formation of strong hydrogen-bonded DME–H2O complexes around 4–14 mol% DME, quasi-aprotic ME appears to induce some order due to the possible formation of H-bonded ME–water complexes around 10–15 mol% ME.

Free energies and entropies of transfer of hydrogen halides from water to aqueous 2-methoxy ethanol and structuredness of the solvents

1985 ◽  
Vol 63 (4) ◽  
pp. 798-803 ◽  
Author(s):  
Prabir K. Guha ◽  
Kiron K. Kundu
Keyword(s):  
Dielectric Constant ◽  
Mixed Solvents ◽  
Three Dimensional ◽  
Halide Ions ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Hydrogen Halides ◽  
Emf Measurements ◽  
Composition Profiles ◽  
The Individual

Standard free energies (ΔGt0) and entropies (ΔSt0) of transfer of HBr and HI from water to some aqueous solutions of 2-methoxy ethanol (ME) have been determined from emf measurements of the cells: Pt, H2 (g, 1 atm)/HBr (m), solvent/AgBr–Ag and Pt, H2 (g, 1 atm)/KOH (m1), KI (m2), solvent/AgI–Ag, respectively, at seven equidistant temperatures ranging from 15 to 45 °C. ΔGt0 values of HBr and HI as well as of HCl obtained from literature, and particularly that of the individual ions obtained by tetraphenylarsonium tetraphenylboron (TATB) assumption, suggest that while H+ is increasingly stabilized by cosolvent-induced larger "basicity", halide ions (X−) are increasingly destabilized by cosolvent-induced decreased "acidity" and the dielectric constant of the mixed solvents compared to that of water. Analysis of the variation of the observed TΔSt0(HX) and particularly of ΔY (= TΔSt0(H+) + TΔS0t.ch (X−), with composition, in the light of Kundu etal's semi-quantitative theory reveals that ME induces breakdown of three dimensional (3D) tetrahedral structures of water at water-rich compositions. This is being followed by an ordered region due to possible H-bonded cosolvent–water complexation and then the usual disordered region due to packing imbalance. Comparison of ΔY(HI)–composition profiles for aqueous mixtures of t-butanol (ButOH), ethylene glycol (EG), and 1,2-dimethoxy ethane (DME) also demonstrates that the remarkable enhancement of 3D water structures by the well known structure promoter ButOH gets succintly diminished when cosolvent ButOH is replaced by EG, ME, and DME, as is expected from structural and electronic considerations of the cosolvents.

Solvent effect on the dissociation of p-nitroanilinium ion in glycerol–water media at 25 °C

1984 ◽  
Vol 62 (11) ◽  
pp. 2245-2248
Author(s):  
Amrita Lal De ◽  
Tapas Kumar De
Keyword(s):  
Solvent Effect ◽  
Dissociation Constants ◽  
Mixed Solvents ◽  
Individual Species ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Monohydric Alcohol ◽  
Glycerol Water ◽  
Alcohol Water ◽  
The Individual

Thermodynamic dissociation constants (sK) of p-nitroanilinium ion (BH+) have been determined at 25 °C in aqueous mixtures of 10, 30, 50, 70, and 90 wt.% of glycerol (GL) by spectrophotometric measurements. Standard free energies, [Formula: see text], of p-nitroaniline (B) from water to mixed solvents have been evaluated from the measurement of solubilities at 25 °C. p(sK) values decrease with increase in mol% of GL and pass through a minimum and then increase very slowly. The solvent effect on the dissociation, δ(ΔG0) = 2.303RT [p(sK)N – p(wK)N] has been discussed in terms of the standard free energies of transfer [Formula: see text] from water to aqueous mixtures of GL of the uncharged base (B), the hydrochloride of the base (BHCl), hydrochloric acid (HCl), and also in terms of the individual species involved in the dissociation process. The solvent effect in trihydric alcohol – water (GL + H2O) system has been compared with those in dihydric alcohol – water (ethylene glycol + water) and monohydric alcohol – water (ethanol + water) systems available from literature. The much less solvent effect in GL + H2O has been primarily attributed to the contrasting nature of interaction of H+ and of partially charged H atoms of—NH3+ group in BH+ compared to those in other two solvent systems.

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