Thermodynamic properties of binary mixtures of tetrahydropyran with pyridine and isomeric picolines: Excess molar volumes, excess molar enthalpies and excess isentropic compressibilities

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Abstract

Densities, ρ and speeds of sound, u of tetrahydropyran (i) + pyridine or α-, β- or γ- picoline (j) binary mixtures at 298.15, 303.15 and 308.15 K and excess molar enthalpies, HE of the same set of mixtures at 308.15 K have been measured as a function of composition using an anton Parr vibrating-tube digital density and sound analyzer (model DSA 5000) and 2-drop micro-calorimeter, respectively. The resulting density and speed of sound data of the investigated mixtures have been utilized to predict excess molar volumes, VE and excess isentropic compressibilities, κSE. The observed data have been analyzed in terms of (i) Graph theory; (ii) Prigogine–Flory–Patterson theory. It has been observed that VE, HE and κSE data predicted by Graph theory compare well with their experimental values.

Research highlights

► Densities, ρ and speeds of sound, u of tetrahydropyran (i) + pyridine or α-, β- or γ-picoline (j) binary mixtures at 298.15, 303.15 and 308.15 K and excess molar enthalpies, HE of the same set of mixtures at 308.15 K have been measured as a function of composition. ► The observed densities and speeds of sound values have been employed to determine excess molar volumes, VE and excess isentropic compressibilities, κSE. ► Topology of the constituents of mixtures has been utilized (Graph theory) successfully to predict VE, HE and κSE data of the investigated mixtures. ► Thermodynamic data of the various mixtures have also been analyzed in terms of Prigogine–Flory–Patterson (PFP) theory.

Introduction

Industry demands reliable and accessible reference data on the thermodynamic properties of binary and ternary liquid mixtures. These properties are required for the development of thermodynamic models, engineering applications along with nature and extent of interactions in liquid mixtures. Cyclic ethers are useful solvents due to strong proton accepting ability. Furthers cyclic ether as alone or their mixtures with aromatic hydrocarbons, alkanols or n-alkanes are used in pharmaceutical and cosmetic processes. This has greatly stimulated the need for extensive information about thermodynamic properties of mixtures containing cyclic ether. In our systematic investigations of thermodynamic properties of binary and ternary mixtures containing cyclic ether, excess molar volumes, VE, excess molar enthalpies, HE, excess Gibbs free energies, GE and excess isentropic compressibilities, κSE data of binary [1], [2], [3] and ternary [4], [5] mixtures have been analyzed in terms of Graph theory (which involves the topology of a molecule). In continuing with our study on thermodynamic properties of cyclic mixtures, we report here the densities, speeds of sound and excess molar enthalpies data of tetrahydropyran (i) + pyridine or α-, β- or γ-picoline(j) mixtures.

Section snippets

Experimental

Tetrahydropyran (THP) (Fluka, 98 mol.%), pyridine (Py) (Fluka, 99 mol.%), α-picoline (Fluka, 98 mol.%), β-picoline (Fluka, 98 mol.%), γ-picoline (Fluka, 99 mol.%) were purified by standard methods [6]. The purities of the purified liquids were checked by measuring their densities (recorded in Table 1) using Anton Parr DSA 5000 at 298.15 ± 0.01 K. These values agreed to within ±2 × 10−3 kg m−3 with their literature values [6], [7]. Excess molar enthalpies, HE for the studied mixtures were measured by a

Results

Densities, ρ and speeds of sound, u of THP (i) + Py or α-, β- or γ-picoline (j) binary mixtures at 298.15, 303.15 and 308.15 K and excess molar enthalpies, HE of the same set of mixtures at 308.15 K are listed in Table 2. Densities and speeds of sound values of mixtures were employed to predict excess molar volumes, VE and isentropic compressibilities, κS usingVE=i=ijxiMi(ρ)1i=ijxiMi(ρi)1κS=(ρu2)1where ρ is the density of mixture and xi, Mi and ρi are the mole fraction, molar mass and density

Discussion

We are unaware of VE, HE and κSE data of the studied mixtures with which to compare our results. Excess molar enthalpies, HE data of (i + j) mixtures are positive over entire composition range and for equimolar composition follow the order: α-picoline  γ-picoline > Py > β-picoline. However, excess molar volumes, VE and excess isentropic compressibilities, κSE values are negative over entire composition range and for equimolar composition vary in the order: Py > β-picoline > γ-picoline > α-picoline; β

Excess molar volumes

Graph theory deals with the topology of the constituents of mixtures. Topology of the pure (i) and (j) components changes on the addition of i to j or vice versa in (i + j) mixture. Since excess molar volumes, VE reflects change in topology of the constituents of mixtures, VE data of (i + j) mixtures were, therefore, analyzed in terms of Graph theory. According to this theory [17], VE is given byVE=αijxi(3ξj)m1xi(3ξj)1where xi is the mole fraction of the component (i) and αij is a constant

Excess molar volumes

According to this theory, excess molar volumes [27], VE is considered to be comprised of three contributions: (i) interaction contribution; (ii) free volume contribution; (iii) the contribution that depends on the difference in both internal pressure and reduced volumes of two components constituting binary mixtures. VE in terms of these three contributions is expressed as:VE=VinteractionE+Vfree-volumeE+VP*effectEwhereVinteractionExivi*=[(v˜1/31)v˜ψiθjχij*][(4/3)v˜1/31]v˜Vfree-volumeExivi*

Acknowledgements

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

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