Excess enthalpies of dimethylsulfoxide with substituted benzenes at 298.15 K

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Abstract

Excess molar enthalpies (HE) at 298.15 K have been measured by a Paar 1451 solution calorimeter as a function of composition for the binary liquid mixtures of dimethylsulfoxide (DMSO) with substituted benzenes. The substituted benzenes include toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene. The HE values for the above mixtures are all positive over the entire composition range. The experimental results have been correlated using the Redlich–Kister (R–K) polynomials. The results are interpreted on the basis of possible hydrogen bonding between unlike molecules and changes in molecular association equilibria as well as structural effects for these systems. The excess enthalpy data have also been correlated with the Peng–Robinson (PR) as well as the Patel–Teja (PT) equations of state (EOS) and also the activity coefficient models of the Wilson and the NRTL.

Introduction

Experimental data of excess thermodynamic properties of liquids and liquid mixtures are of great fundamental and practical importance. These properties allow one to draw information on the structure and interactions of mixed solvents. The chemical industries have recognized the importance of the thermodynamic properties in design calculations involving chemical separations, heat transfer, mass transfer and fluid flow. Dimethylsulfoxide (DMSO) is a highly polar (μ = 4.06 Debye) [1] and self-associated solvent [2] and has ability to participate in hydrogen bonding [3]. It has a large dipole moment, high dielectric constant (ɛ = 46.45) [1] and polarizability [4] and these enable to stabilize molecules and ions through dipole and induced-dipole interactions. In liquid mixtures, the enhancement of its donor ability may result from the breaking of DMSO structure by the addition of second liquid component [5]. It is less toxic and an effective paint stripper, being much safer than many of the other polar solvents. Since, DMSO as a solvent of its high boiling point, thus its solutions are not typically evaporated but instead diluted to isolate the reaction product.

In recent years the thermodynamic properties of dimethylsulfoxide (DMSO) with substituted benzenes have received increasing attention because they serve as model compounds in biochemical considerations [6], [7], [8]. The excess molar enthalpy (HE) of binary mixtures containing DMSO + cycloethers [9], +hexamethylphosphoric trimide [10], +water [11], +dialkylethers [12], +halogenized aromatic compounds [13], [14], +dihalogenized benzenes [15], +N,N-dimethylethanolamine [16], +alkylbenzenes [17], +1-alkynes [18], +alkane-1-amines [19], +aliphatic alcohols [20], +aliphatic alcohols or aliphatic nitriles [21], +normal alcohols [22], +ketones [23] have been appeared in the literature. However, no effort appears to have been made to collect the HE for the mixtures of DMSO with substituted benzenes and there is no evidence for specific interactions of DMSO with substituted benzenes. In addition, these liquids were chosen in the present investigation on the basis of their industrial importance. DMSO, toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene are important liquids which find a variety of applications such as solvents for lacquers, oils and resins [4], [6].

In order to extend our research programs to explore the interactions between the highly polar groups with other solvents [6], [23], [24], [25], [26], [27], [28], [29], [30], and to characterize the type and the magnitude of molecular interactions between the polar group solvents, we report here the HE at T = 298.15 K and atmospheric pressure of binary mixtures containing DMSO with toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene. Moreover, the experimental HE data were correlated with the Peng-Robinson (PR) [31] and the Patel-Teja (PT) [32] equations of state and also the activity coefficient models of the Wilson [33] and the NRTL [34] for the binary systems.

Section snippets

Materials

The pure solvents of highest purity commercially available were used in the present investigation. DMSO and substituted benzenes were purified by the standard methods described by Riddick et al. [1]. The purity of the samples was checked by measuring densities and boiling points. The densities were measured using a standard bicapillary pycnometer, giving an accuracy of 2 parts in 105. Boiling points at 95.3 kPa were measured by Swietoslawski-type ebulliometer [35] with an accuracy of ±0.2 K. The

Results

The measured HE values of DMSO with substituted benzenes at 298.15 K are reported in Table 2 and shown graphically in Fig. 1 as a function of mole fraction of substituted benzenes. The experimental HE results of each binary system were fitted with the smoothing functions by the Redilich–Kister (R–K) type equation using the polynomial form:HEJmol1=x1(1x1)ihi(2x11)iwhere hi are coefficients for the binary systems and are collected in Table 3 along with the percentage standard deviation. The

Data correlation

The HE data have been correlated with the PR [31] and the PT [32] equations of state and also the activity coefficient models of the Wilson [33] and the NRTL [34] for all the binary systems. The properties of pure compounds are collected in Table 4. The calculated values of HE from the various models are also included in Table 2. The correlated results of the equations of state (the PR and the PT) and the activity coefficient models (the Wilson and the NRTL) are reported in Table 5, Table 6,

Discussion

The measured HE values are positive (endothermic) in all the mixtures of DMSO with substituted benzenes over the entire range of composition. The maximum positive HE value is observed for the above systems around 0.5 mol fraction. Excess enthalpy data may be interpreted by considering two factors: (a) loss of dipolar association due to the addition of one component to the other and difference in sizes between unlike molecules and (b) dipole–induced dipole and dipole–dipole interactions and

Acknowledgments

One of the authors (MRM) is highly thankful to University Grants Commission (UGC), New Delhi, India, for providing a teacher fellowship. Furthermore, MRM would like to grateful to Dr. D.H.L. Prasad, Indian Institute of Chemical Technology (IICT), Hyderabad, India for provided Paar 1451 solution calorimeter to carry out the HE measurements.

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