Thermodynamic Properties of Salophen Schiff Base + Ionic Liquid ([C n mIm][Br]) + Dimethylformamide Ternary Mixtures at 298.15 K Hemayat Shekaari,* ,† Abolfazl Bezaatpour, ‡ and Rasoul Elhami-Kalvanagh § † Department of Physical Chemistry, University of Tabriz, Tabriz, Iran ‡ Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, Ardabil, Iran § Department of Chemistry, Mamaghan Branch, Islamic Azad University, Mamaghan, Iran ABSTRACT: The densities and viscosities of ternary mixtures of N,N′-salicylidene- phenylenediamine Schiff base (Salophen) + ionic liquid + N,N-dimethylformamide (DMF) have been determined at 298.15 K and at atmospheric pressure. The ionic liquids were: 1-propyl-3-methylimidazolium bromide ([C 3 mIm][Br]), 1-butyl-3- methylimidazolium bromide ([C 4 mIm][Br]), 1-pentyl-3-methylimidazolium bromide ([C 5 mIm][Br]), and 1-hexyl-3-methylimidazolium bromide ([C 6 mIm][Br]). These data have been used to calculate the standard partial molar volumes, V ϕ 0 , transfer partial molar volumes, Δ tr V ϕ 0 , and viscosity B-coefficients for the investigated mixtures. An increase in concentration and alkyl chain length of ionic liquid results in a decreasing trend in the calculated volumetric and viscometric parameters. All of these parameters were used to interpret the effect of ionic liquids on the nonaqueous solutions of Salophen Schiff base and solute-solvent interactions occurring between the various components. ■ INTRODUCTION Ionic liquids (ILs) are a new class of organic salts containing an asymmetric organic cation and noncoordinating inorganic anion. Owing to their unique chemical and physical properties, such as negligible vapor pressure ([C 4 mIm][PF 6 ] is 10 -10 Pa at 298 K), 1 good thermal stability, a wide liquid range, excellent solvent power for organic and inorganic and polymeric compounds, suitable viscosity, and nonflammability, easy recyclability, and reusability, they have been recognized as an alternative solvent for organic and inorganic synthesis. 2-5 Recently, ILs have been applied to transition metal catalysis containing Schiff base ligands with the benefit of a convenient catalyst separation, hence, an easy recovery/recycling proce- dure. The efficiency of such a catalyst/IL system is strongly dependent on the nature of the ILs. The presence of ILs modifies many important properties of transition metal catalysis containing a Schiff base and their derivatives related to their thermophysical properties, such as density and viscosity. The Schiff base ligand has imine groups that are produced by the condensation reactions of aldehydes, ketones, or β-ketones with primary amines and related derivatives which are used extensively, as important groups of ligands in coordination chemistry, medicine, agriculture, industry, and electronics. 6-16 Some studies have been reported on the application of ILs in the processes containing the Schiff base ligand. A new cyanide optode was designed using a [N,N′ -bis(salicyliden)-2,3- diaminopyridine] tributylphosphine cobalt(III) percholorate monohydrate complex. The reduction in the absorbance value of the optode at the maximum wavelength of 380 nm was related to cyanide concentration in aqueous samples. The sensitivity of the method was improved by using an IL, 1-butyl- 3-methylimidazolium hexafluorophosphate, [C 4 mIm][PF 6 ], introduced in constructing the optode membrane. 17 A novel Schiff base extracting agent (PMBP-2-ABT) was synthesized and used for the extraction of heavy metal ions by PMBP-2- ABT/IL binary-water phase system. In IL binary-water phase system, PMBP-2-ABT was an excellent extracting agent for heavy metal ions. 18 The generalized use of these new compounds needs an accurate knowledge of their thermodynamic properties both when pure and when they are mixed with compounds. The study of thermodynamic properties of Schiff base in the presence of IL mixtures is crucial from a technological point of view, but it also provides a better understanding of the mechanisms involved when using these new media. For example, their volumetric and viscometric properties of the mixtures have been used to provide information on solute- solvent interactions in mixtures. However, there are not any reports on the thermodynamic properties of Schiff base ligand in the presence of ILs according to our literature survey. This work is a continuation of systematic studies on the thermodynamic properties of Schiff base ligands in the presence of ILs. In this work, we report the density, d, and viscosity, η, of N,N′-salicylidenephenylenediamine (Salophen) Schiff base (Figure 1) + IL + N,N-dimethylformamide (DMF) ternary mixtures at several concentrations of ILs. The ILs were: 1- propyl-3-methylimidazolium bromide ([C 3 mIm][Br]), 1-butyl- 3-methylimidazolium bromide ([C 4 mIm][Br]), 1-pentyl-3- Received: August 7, 2011 Accepted: January 8, 2012 Published: January 26, 2012 Article pubs.acs.org/jced © 2012 American Chemical Society 345 dx.doi.org/10.1021/je200872n | J. Chem. Eng.Data 2012, 57, 345-351