Thermodynamic properties of binary mixtures containing tetrahydropyran: Excess molar volumes, excess molar enthalpies and isentropic compressibilities changes of mixing

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Abstract

Excess molar volumes, VE, excess molar enthalpies, HE and speeds of sound, u data of tetrahydropyran (i) + cyclohexane or n-hexane or n-heptane (j) binary mixtures have been measured using dilatometer, calorimeter and interferometer over whole mole fraction range at 308.15 K. Speeds of sound data have been utilized to predict isentropic compressibilities changes of mixing, κSE. The analysis of VE in terms of Graph theory reveals that (i + j) mixtures are characterized by dipole–induced dipole interactions between THP and cyclo or n-alkanes to form 1:1 molecular complex. HE and κSE data of the investigated mixtures have also been analyzed in terms of Graph theory. VE, HE and κSE data predicted by Graph theory compare well with their corresponding experimental values.

Introduction

The systematic study of thermodynamic properties has greater importance to extract information about the molecular interactions among the constituents of mixtures. Knowledge of thermodynamic properties is also essential for the proper design of industrial processes. The nature and relative strength of molecular interactions operating among the components of liquid mixtures have been successfully predicted by measuring their thermodynamic properties like excess molar volumes, excess molar enthalpies, excess Gibbs free energies of mixing and isentropic compressibilities changes of mixing and analyzing them in terms of topology of constituents of mixtures, Homomorph concept, UNIFAC, EBGCM, Nagamachi models and Graph theory of liquid mixtures [1], [2], [3], [4], [5], [6], [7], [8]. Cyclic ethers represent a class of technically important compounds frequently used as solvent in chemical industry. Tetrahydropyran is used in polymerization processes, pharmaceutical industries as a reaction intermediate [9]. A recent study [10] has shown that tetrahydropyran (i) + aromatic hydrocarbons (j) binary mixtures are characterized by interactions between dipole of tetrahydropyran and π-electron cloud of benzene ring of aromatic hydrocarbons to form 1:1 molecular complex. It would be of interest to see how these interactions are influenced when aromatic hydrocarbons are substituted by cyclo or n-alkanes. These considerations prompted us to measure excess molar volumes, VE, excess molar enthalpies, HE and speeds of sound data of THP (i) + cyclohexane or n-hexane or n-heptane (j) binary mixtures.

Section snippets

Experimental

Tetrahydropyran (THP) (Fluka: >99.5 moles percent purity), cyclohexane (E. Merck: >99 moles percent), n-hexane (E. Merck: > 99.5 moles percent), n-heptane (E. Merck: >99 moles percent) were purified by standard methods [11]. The purities of the purified liquids were checked by measuring their densities using bi-capillary pycnometer (recorded in Table 1) at 298.15 ± 0.01 K and these agreed to within ±5 × 10−5 kg m−3 with their corresponding literature values [11]. Excess molar volumes, VE for binary (i + j)

Results

The measured excess molar volumes, VE, excess molar enthalpies, HE and speeds of sound, u data of tetrahydropyran (i) + cyclohexane, n-hexane and n-heptane (j) binary mixtures over entire composition range at 308.15 K are recorded in Table 2, Table 3, Table 4. The isentropic compressibilities, κS for (i + j) binary mixtures were determined from their speeds of sound data using relation:κS=(ρiju2)1

The densities, ρij of binary mixtures were evaluated from their excess molar volumes data (reported in

Discussion

Excess molar volumes, VE values of THP (i) + n-hexane (j) mixtures are lesser (Fig. 1) by 0.004 cm3 mol−1 from the values reported in the literature [22], [26] at 303.15 K.Excess molar enthalpies, HE data of THP (i) + cyclohexane (j) mixtures at 308.15 K agree to within ±10 Jmol−1 (Fig. 2) with their literature values [20]. Further, HE values of THP (i) + n-hexane or n-heptane (j) mixtures differ by 4–5% than the values reported for these mixtures at 298.15 K [21], [22], [23]. Our VE values for THP (i) + 

Graph theory and results

The addition of THP (i) to cyclohexane or n-heptane or n-hexane (j) may change the topology of (i) or (j) in the mixed state. Excess molar volumes, VE reflects change in topology of the constituents of the mixtures, so it was worthwhile to analyze the observed VE data in terms of Graph theory. According to Graph theory [27], VE is given by:VE=αijxi(ζi3)m1xi(ζi3)1where αij is a constant characteristic of (i + j) mixture and xi is the mole fraction of component (i). (3ξi) (i = i or j) and (3ξi)m

Acknowledgements

The authors are thankful to the Head, Department of Chemistry and authorities of Maharshi Dayanand University, Rohtak, for providing research facilities.

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