A Study of Solute–Solvent Interaction in Solvents of Medium Dielectric Constant from the Apparent Molal Volume Data. I

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Abstract
A study of the apparent molal volume (φv) of some common salts and the tetraalkylammonium iodides in DMSO has been reported in this communication. All the salts studied here, including those containing the larger R4N+ ions, have a positive slope in the φv vs. \sqrtC curves, indicating a strong ionic interaction, apparently due to the medium dielectric constant of the solvent. This dielectric constant also promotes ion-association at higher concentrations and thus mutual penetration of the R4N+ ions is prevented. As a result, no negative slope in the φv vs. \sqrtC curves of the larger R4N-iodides is observed in this solvent. The effect of temperature on the limiting apparent molal volume, φ°, reveals that the ion-solvent interaction is comparatively stronger in the non-hydrogen bonded solvents like DMSO and DMF than that in strongly hydrogen-bonded solvents like NMA and NMP. Addition of a CH2-group to each of the four R-chains of the R4N+ ion increases its volume by about 70 ml per mole in DMSO, DMF, and NMA.