Effect of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane Schiff base (BPIE) on the thermodynamic properties of the ionic liquid 1-hexyl-3-methylimidazolium chloride in N,N-dimethylacetamide solvent at T = 298.15 K

doi:10.1016/j.jct.2014.09.022

The Journal of Chemical Thermodynamics

Volume 81, February 2015, Pages 131-135

https://doi.org/10.1016/j.jct.2014.09.022 Get rights and content

Highlights

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The effect of BPIE Schiff base on the thermodynamic properties of an ionic liquid in DMA was studied.
•
Densities, viscosities, and refractive indices of the ternary mixtures were measured.
•
Some important parameters, such as $V_{ϕ}^{0}$ and viscosity B-coefficient were calculated.
•
(Polar + nonpolar) and (nonpolar + nonpolar) interactions between the ionic liquid and BPIE were confirmed.
•
The IL showed a structure-breaking ability in DMA that this tendency decreased in the presence of the Schiff base.

Abstract

Densities, viscosities, and refractive indices of ternary mixtures of ionic liquid 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) + Schiff base, N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE), a mixture of cis- and trans-isomers, + N,N-dimethylacetamide (DMA) were measured at T = 298.15 K. From the obtained data, apparent molar volumes ( $V_{ϕ}$ ), corresponding experimental slopes (S_v), standard partial molar volumes ( $V_{ϕ}^{0}$ ), transfer volumes ( $Δ_{t} V_{ϕ}^{0}$ ), viscosity B-coefficients, solvation numbers (S_n), and molar refractions ( $R_{D}$ ) were calculated and discussed on the basis of (solute + solvent), and (solute + cosolute) interactions. As stated by cosphere overlap model (Yan et al., 2009), the negative transfer volumes obtained here show the dominance of (polar + nonpolar) interactions between the polar group of BPIE and the nonpolar alkyl chain of [HMIm]Cl and (nonpolar + nonpolar) interactions between the nonpolar groups of BPIE and the alkyl chain of [HMIm]Cl. The values of solvation numbers (S_n) were obtained as S_n > 2.5 and decrease as the concentration of BPIE in the mixtures increases. The S_n > 2.5 means that the IL is solvated in the mixtures, but the decreasing the S_n values indicates that the solvation of the ions of the ionic liquid decreases at higher concentrations of the Schiff base.

Introduction

Schiff bases are products from the condensation of primary amines with carbonyl compounds that were first reported by Schiff [1] in 1864. The common structural feature of Schiff bases is the azomethine group with a general formula RHC double bond N single bond R′, where R and R′ are alkyl, aryl, cyclo alkyl, or heterocyclic groups that may be variously substituted. Schiff bases are present in various industrial processes, such as optical materials and conducting polymers [2], [3]. They are containing amphiphiles in polymeric films that show interesting optical and electronic properties [4], [5]. They are also used in catalytic, antimicrobial, antifungal, antiviral applications, plant growth regulation, and dying applications [6]. In addition, several complexes of the tetradentate Schiff base ligand, N, $N^{'}$ -bis(salicylidene)ethylenediamine (salen), have been proposed as insulin mimetic agents for potential usages [7]. Schiff bases have also been introduced as effective corrosion inhibitors for steel, copper, and aluminum, which act by adsorption on the metal/solution interface [8], [9], [10].

Recently, several works have been reported on Schiff bases and their metal complexes in the presence of ionic liquids (ILs) [11], [12], [13]. Ionic liquids are solvents with a relative high polarity and a broad ability to dissolve organic and inorganic compounds. It has been reported that ionic liquids are attractive solvents for oxidation catalytic reactions, such as alkene epoxidations [11] and asymmetric synthesis of cyanohydrins catalyzed by Schiff base complexes [12]. Surprisingly, it was found that the activity of Schiff base complexes as catalysts increased by adding ionic liquids to the reaction medium [13]. Moreover, the addition of co-solvents has been found to affect strongly various physico-chemical properties of ionic liquids, and this becomes further important when the solubility of reactants in ionic liquids is limited. The mixed organic solvents and ionic liquids can be used advantageously to achieve homogeneous systems in which the reactants and catalysts have the best solubility. DMA is one the known organic solvents to interact strongly with metal cations to leave non-solvated anions. DMA is a polar aprotic solvent with good properties for nonaqueous chemistry. It has a moderate relative permittivity (37.8), a wide liquid range, and a room temperature viscosity close to water. The oxygen atom in the carbonyl group is at the negative end of the molecular dipole and is the site at which cation solvation occurs.

Various thermophysical thermodynamic properties of the systems composed of Schiff base, ionic liquid, and molecular solvents can provide useful information about (solute-solvent) and (solute-cosolute) interactions that would permit developing a suitable experimental procedure for a convenient catalytic system.

This paper is a continuation of our previous studies [14], [15] on the thermodynamic properties of the nonaqueous BPIE Schiff base in the presence of an ionic liquid. In this work, we have reported some thermodynamic properties including density, viscosity and refractive index of the ternary mixtures ([HMIm]Cl + BPIE + DMA) at T = 298.15 K and the results discussed in terms of the (ion + ion) or (solute + solute), (ion + solvent) or (solute + solvent), and (solute + cosolute) interactions.

Section snippets

Materials

The chemicals used in this work are N-methylimidazole (>99%), 1-chlorohexane (>99%), N,N-dimethylacetamide (>99.8%), ethyl acetate (>99%), pyridine-2-aldehyde (>99.8%), and ethylenediamine (>99.9%). The density and viscosity of DMA at T = 298.15 K have the values 936.31 kg · m⁻³ and 0.989 × 10⁻³ Pa · s, respectively that are in good agreement with the literature values 935.287 kg · m⁻³ [16] and 0.945 × 10⁻³ Pa · s [17], [18] (see table 1).

Synthesis of the ionic liquid and the Schiff base

The ionic liquid 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl) was

Volumetric properties

Volumetric properties are considered sensitive tools to understand molecular interactions in mixtures. To obtain these properties, experimental densities (d) of the ternary mixtures of the ([HMIm]Cl + BPIE + DMA) as a function of [HMIm]Cl molality (m_IL) were measured at T = 298.15 K (reported in table 2). From the density values, apparent molar volumes ( $V_{ϕ}$ ) of [HMIm]Cl in (BPIE + DMA) mixtures were calculated using the following equation $V_{ϕ} = \frac{M}{d} - \frac{(d - d_{0})}{m_{IL} {dd}_{0}},$ where M is the molar mass of [HMIm]Cl, m_IL is

Conclusions

Densities, viscosities, and refractive indices of the ternary mixtures (1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) + N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) + N,N-dimethylacetamide (DMA)) were measured at T = 298.15 K. The positive values obtained for $V_{ϕ}^{0}$ and viscosities B-coefficient demonstrate that there is (solute + solvent) interactions in the mixtures, and these interactions are weakened at higher BPIE concentrations. The transfer volumes ( $Δ_{t} V_{ϕ}^{0}$ ) have negative values and

Acknowledgments

All the laboratory work of the present paper has been performed in the University of Mohaghegh Ardabili. The authors would like to thank financial support from the Graduate Council of this university. The authors also greatly appreciate Dr. A. Bazaatpour, the head of Inorganic Chemistry Research Laboratory in University of Mohaghegh Ardabili, to help in the synthesis of the Schiff base and for his constructive comments in this project.

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Effect of N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane Schiff base (BPIE) on the thermodynamic properties of the ionic liquid 1-hexyl-3-methylimidazolium chloride in N,N-dimethylacetamide solvent at T = 298.15 K

Highlights

Abstract

Introduction

Section snippets

Materials

Synthesis of the ionic liquid and the Schiff base

Volumetric properties

Conclusions

Acknowledgments

Tetrahedron

J. Lumin.

Chem. Phys. Lett.

Corros. Sci.

Corros. Sci.

Tetrahedron

Catal. Commun.

Thermochim. Acta

J. Chem. Thermodyn.

J. Mol. Struct.

Chem. Phys. Lett.

J. Chem. Thermodyn.

J. Mol. Liq.

Biophys. Chem.

J. Mol. Liq.