Experimental and Theoretical Determination of the Limiting Partial Molar Volume of Indole in CCl4, Tetrahydrofuran and Acetonitrile at 293.15 K: A Comparative Study with Benzimidazole and Benzothiophene

Abstract

The partial molar volumes of indole(Ind) at infinite dilution (\(V_{2}^{\infty}\)) in carbon tetrachloride (CCl4), acetonitrile (ACN) and tetrahydrofuran (THF) as solvents, were estimated from densitometry measurements at 293.15 K. The results indicate that \(V_{2}^{\infty}\mbox{(ACN)}>V_{2}^{\infty}\mbox{(CCl$_{4}$)}\) \(\approx V_{2}^{\infty}\mbox{(THF)}\). The values determined in this study are close to the values calculated from reported density for Ind in the solid state. In order to make a comparison the partial molecular volume of benzimidazole (Bim) and benzothiophene (BT) in solvents with appropriate solubility were measured too, and the results have revealed that \(V_{2}^{\infty}\mbox{(BT)}>V_{2}^{\infty}\mbox{(Ind)}\) in CCl4 and \(V_{2}^{\infty}\mbox{(Ind)}>V_{2}^{\infty}\mbox{(Bim)}\) in THF. In this work the role of solvent reorganization around to solute cavity, and specific and nonspecific interactions on the volumetric behavior of these molecules in solution are discussed using the Terasawa-Itsuki-Arakawa model, the Lee-Graziano model, molar volumes of solutes calculated at the DFT-B3LYP/cc-pVTZ and aug-cc-pVTZ level in the gas phase and considering solvent presence with the Onsager’s reaction field, and the van der Waals volume. This analysis suggests that the molecular volumes of solutes are overestimated by the quantum methods employed in this work and that the volumetric contribution from the van der Waals components to the limiting partial molecular volumes of solutes is important, with the exception of Ind in CCl4 where the solvent reorganization is the dominant factor.