Thermodynamics of transfer of p-nitroaniline from water to alcohol + water mixtures at 25 °C and the structure of water in these media

Abstract

Free energies (ΔGt0) and entropies (ΔSt0) of transfer at 25 °C of the nonelectrolyte p-nitroaniline from water to various alcohol + water mixtures have been determined from solubility measurements at seven temperatures from 10–40 °C. Increasing specific solute–solvent interactions have been proposed to interpret the nature of the ΔGt0-composition profiles and the enhanced structure of water in the water-rich mixed solvents has been correlated with maxima in the ΔSt0-composition profiles. The effectiveness of p-nitroaniline as a useful probe for studying solvent structure has been pointed out.

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

“…The observed upward trend after the initial downward trend imparting roller-coaster type behaviour is seemingly the result of possible hydrogen bonded intercomponent complexation of the type E, making the solvents at these compositions somewhat more ordered. Such type of intercomponent complexes were attributed to similar upward trends observed in AY(HX)-composition profiles (6) or AS:-composition profiles for p-nitroaniline (27) or benzoic acid (28) especially in aqueous mono-01s at higher compositions.…”

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

“…Water used was triply distilled. pNA (Reidel) was used after recrystallizing twice from 75% ethanol and then drying in vncuo, as before (9).…”

“…The method adopted for the measurement of solubility of pNA in different solutions was essentially similar to that described earlier (9). The saturated solutions were diluted with water as required.…”

“…In a series of papers (6), we have examined the observed characteristic maxima of AS: of hydrogen halides (HX) in aqueous mono-01s in the light of "four-step transfer process" (7) and demonstrated from a semiquantitative theory (6) that AS: (HX) might serve as a structural probe. But in view of the fact that electrostatic effect accompanying the transfer of HX is likely to eonfuse the issue, we have also extended these studies with some suitable nonelectrolytes like benzoic acid (HBz) (8) and p-nitroaniline (pNA) (9) as probes. In fact, by adopting a logical model of these amphiphilic solutes and introducing appropriate modifications of the "four-step transfer process", we have demonstrated (8,9) that AS: of these non-electrolytes as well might serve as suitable structural probes.…”

“…But in view of the fact that electrostatic effect accompanying the transfer of HX is likely to eonfuse the issue, we have also extended these studies with some suitable nonelectrolytes like benzoic acid (HBz) (8) and p-nitroaniline (pNA) (9) as probes. In fact, by adopting a logical model of these amphiphilic solutes and introducing appropriate modifications of the "four-step transfer process", we have demonstrated (8,9) that AS: of these non-electrolytes as well might serve as suitable structural probes. Very recently (lo), however, when we applied AS: of HBz as a structural probe in various aqueous ionic and non-ionic cosolvents like LiC1, KBr, D, acetonitrile (ACN), PG, and GL, it appeared that the conclusions derived for these non-ionic cosolvents are at variance not only with those obtained from earlier studies but also with that expected from structural and electronic consideration.…”