Elsevier

Thermochimica Acta

Volume 499, Issues 1–2, 20 February 2010, Pages 149-154
Thermochimica Acta

Solute–solvent and solvent–solvent interactions of menthol in isopropyl alcohol and its binary mixtures with methyl salicylate by volumetric, viscometric, interferometric and refractive index techniques

https://doi.org/10.1016/j.tca.2009.12.001Get rights and content

Abstract

The apparent molar volume (V), viscosity B-coefficient, isoentropic compressibility (ϕK) of menthol have been determined in binary solution of isopropyl alcohol and methyl salicylate (at 303.15, 313.15 and 323.15 K) from density (ρ), viscosity (η) and sound speed respectively. The apparent molar volumes have been extrapolated to zero concentration to obtain the limiting values at infinite dilution using Masson equation. The infinite dilution partial molar expansibilities have also been calculated from the temperature dependence of the limiting apparent molar volumes. Viscosity B-coefficients has been calculated using Jones–Dole equation. The structure-making or breaking capacity of the solute under investigation has been discussed in terms of sign of (δ2VØo/δT2)P. The activation parameters of viscous flow were determined and discussed by application of transition state theory.

Introduction

The volumetric, viscometric and interferrometric behavior of solutes has been proved to be very useful in elucidating the various interactions occurring in pure and mixed solvents. Studies on the effect of concentration and temperature on the apparent molar volumes of solutes have been extensively used to obtain information on ion–ion, ion–solvent, and solvent–solvent interactions [1], [2], [3]. It has been found by a number of workers [4], [5], [6] that the addition of a solute could either make or break the structure of a liquid.

In this paper we have attempted to study the behavior of menthol in isopropyl alcohol (I.P.A.) and in its mixture with methyl salicylate (5, 10 and 15 mass%) at various temperatures because of their extensive use in pharmaceutical and cosmetic industries. Methyl salicylate has a long history of use in consumer products as a counterirritant and as an analgesic in the treatment and temporary management of aching and painful muscles and joints. Methyl salicylate is also used as an UV absorber and in perfumery as a modifier of blossom fragrances [7]. I.P.A. is widely used as a cleaning agent, a cost-effective preservative for biological specimens and is a major ingredient in “dry-gas” fuel additive. Menthol, an old remedy in Chinese medicine extracted from plants of the genus Mentha, is widely used as both a cooling agent and a counterirritant for relieving pain especially in the muscles, viscera or remote areas [8], as well as for the treatment of pruritus.

Section snippets

Chemicals

Menthol (Thomas Baker, >99%) was used as such without further purification. Isopropyl alcohol (Merck, >99.5%) and methyl salicylate (Sigma–Aldrich, >99%) were used with no further purification other than being dried with molecular sieves. Experimental values of viscosity (η), density (ρ), sound speed (u) and refractive indices (nD) of the pure solvents were compared with the literature values and are listed in Table 1.

Measurements

Densities (ρ) were measured with an Ostwald–Sprengel type pycnometer having a

Results and discussions

Apparent molar volumes (V) were determined from the solution densities using the following equation:VØo=Mρo1000(ρρo)cρowhere M is the molar mass of the solute, c is the molarity of the solution; ρ0 and ρ are the densities of the solvent and the solution respectively. The limiting apparent molar volumes VØo was calculated using a least-square treatment to the plots of V versus √c using the Masson equation [13].VØ=VØo+Sv*cwhere VØo is the partial molar volume at infinite dilution and Sv*

Conclusion

The values of apparent molar volume (VØo), viscosity B-coefficients and isoentropic compressibility (ØKo) indicate the presence of strong solute–solvent interactions and these interactions are strengthened at higher temperature and weakened with increasing mass percent of methyl salicylate in the binary solution.

Acknowledgement

The authors are grateful to the Departmental Special Assistance Scheme, Department of Chemistry, NBU under the University Grants Commission, New Delhi (No. 540/27/DRS/2007, SAP-1) for financial support in order to continue this research work.

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