Elsevier

Thermochimica Acta

Volume 590, 20 August 2014, Pages 116-126
Thermochimica Acta

Densities, viscosities, sound speed, and IR studies of N-methyl-2-pyrrolidone with cyclohexylamine, cyclohexanol, and cyclohexene at different temperatures

https://doi.org/10.1016/j.tca.2014.06.026Get rights and content

Highlights

  • Density, sound, speed, and viscosities are measured at a temperature range of 303.15–318.15 K.

  • Excess thermodynamic properties are computed.

  • All the binary systems under study are non ideal solutions.

  • Thermodynamic findings are in good agreement with IR data.

Abstact

Densities, viscosities, and speeds of sound of the binary liquid mixtures of N-methyl-2-pyrrolidone (NMP) with cyclohexylamine (CHA), cyclohexanol (CHOL) and cyclohexene (CHE) at temperatures of 303.15–318.15 K are measured over the entire composition range. From the experimental values excess molar volume VmE, deviation in isentropic compressibility Δks, excess free length LfE, deviation in viscosity Δη are computed. The variation with the temperature and concentration is discussed in terms of molecular interactions. All the excess parameters and deviations are fitted to Redlich–Kister polynomial equation to estimate the binary interaction parameters and mean deviation from the regression lines. The sign and magnitude of the computed parameters are discussed to reveal the nature and type of interactions existing between the component molecules in the binary mixtures. Thermodynamic investigations under the present study reveal the strong inter molecular interactions between the unlike molecules in the binary systems of NMP + CHA, NMP + CHOL, whereas in the other binary system NMP + CHE the reverse trend is observed due to dispersion forces. The strength of interaction of CHA, CHOL, and CHE with NMP found to follow the order: CHA > CHOL > CHE. FT-IR studies of these mixtures have been estimated and analyzed to study the interactions between unlike molecules. A good agreement is observed between the excess parameters and FT-IR studies.

Introduction

Thermodynamic, transport, and spectroscopic studies of binary liquid mixtures provide information on the nature of interactions in the constituent binaries. In chemical industry, the density, viscosity of multicomponent mixtures containing non-electrolyte solutions are required in many chemical engineering calculations involving chemical separations, fluid flow, mass, and heat transfer [1], [2], [3]. The excess values of binary liquid mixtures are useful in understanding the nature and strength of interactions in the mixtures [4], [5]. The interaction between solvents with polar groups and polar compounds plays a crucial role in the structural effects, molecular level, and for practical application. The deviation from ideality is expressed by many thermodynamic variables particularly by excess properties [6]. Derived thermodynamic and acoustical parameters like excess molar volume, isentropic compressibility, excess free length, and deviation in viscosity are of considerable interest in understanding the inter-molecular interactions in binary liquid mixtures.

Lactams are significant class of amides not extensively studied; despite their use as solvents and biologic applications, their solution properties are still not well understood. Hence, one of the lactams, N-methyl-2-pyrrolidone (NMP), is chosen as a common solvent for the present study. NMP is a colorless, high boiling, mobile, characteristic odor, and low viscous liquid known for its low toxicity and solvent power, is rapidly becoming the product of choice for agricultural chemicals, paint strippers, purification, and crystallization of drugs [7] and process solvent applications. As a co-solvent, NMP can improve the gloss of floor polishes, and it is has application in the electronic industry as a photo-resist stripper. In addition, NMP is a strong polar liquid and has the potential for use in solvent extraction process for separation of polar substances from non-polar substances. A fundamental understanding of the behavior of NMP in its binary mixtures with polar and non-polar solvents is important from the technical and engineering point of view. Further, it has excellent thermal and chemical stability and is used as absorbent of sour gases from crude natural gas.

Among the cyclic compounds, cyclohexylamine [8], an organic synthesizer,which acts as a corrosion inhibitor finds applications in the manufacture of plasticizers, detergents, insecticides, and emulsifiers. Cyclohexanol [8] finds applications as an intermediate substance in the production of nylon and plasticizers. It acts as a stabilizer in soap and detergent making and as a solvent in paint and textile industries. Cyclohexene [8] is used in oil refining as a stabilizer. Also, these three cyclic compounds are highly used as solvents in organic synthesis.

A survey of the literature shows that few groups of compounds are studied with NMP. With ketones by Gnana Kumari et al. [9], with water by George and Sastry [10], xylene with NMP by Yang et al. [11], with ammonium ionic liquids by Venkatesu and co-workers [12], aromatic hydrocarbons by Ye et al. [13], aqueous solutions of NMP by Henni et al. [14], isomeric butanediol with NMP by Mehta et al. [15], with N,N-dimethylformamide by Yang et al. [16], with monoetanolamine and diethanolamine by Hernandez et al. [17], with propoxy etanols by Pal and Bharadwaj [18], with ethylbenzene by Yang et al. [19], with xylene at different temperatures by Chen et al. [20], with dipropylene glycol monobutyl ether and dipropylene glycol tert-butyl ether by Pal and Kumar [21], with (C1–C10) alkan-1-ols by Garcia et al. [22].

Though the literature provides extensive data on the density and viscosity of binary liquid mixtures, but a combined study of density, viscosity, ultrasonic velocity, and FT-IR is quite scare. To the best of our knowledge, no experimental data, on thermo acoustic parameters, and FT-IR are available in the literature for (NMP + CHA), (NMP + CHOL) and (NMP + CHE) binary liquid systems. In continuation of our research work on phase equilibrium, thermodynamic, and thermo acoustic studies of NMP [23], [24], [25], [26], [27], in this paper, we present the speeds of sound, densities, viscosities in the temperature range 303.15–318.15 K at an interval of 5 K and atmospheric pressure over the entire composition range. We also present infrared data of the binary mixtures at room temperature. The aim of this work is to provide a set of data in order to assess the influence of the temperature and concentration of NMP on the molecular interactions between NMP and cyclic compounds. An attempt has been made to understand the influence of hydrogen bond on excess properties of the binaries investigated. The excess properties computed for all the binary mixtures are correlated with the Redlich–Kister polynomial type equation.

Section snippets

Materials

NMP (Merck India, >0.995 mol fraction purity) is distilled at low pressure and stored over freshly activated 0.3 nm molecular sieves. Cyclohexylamine (>0.995 mol fraction purity, SD Fine Chemicals, India) is dried over molecular sieves and fractionally distilled over sodium, followed by fractional distillation under dry nitrogen [28]. Cyclohexanol (>0.995 mol fraction purity, SD Fine Chemicals, India) is purified by refluxing for 24 h over freshly ignited lime, followed by fractional distillation.

Theory

Using experimental values of ultrasonic velocity (u), density (ρ), viscosity (η), acoustic, and thermo dynamical properties like molar volume, isentropic compressibility, free length, and deviation in viscosity are evaluated.Molar volume VmE=[x1M1+x2M2ρx1M1ρ1x2M2ρ2]Isentropic compressibility ks=1ρU2Free length LfE=KJ(ks)1/2

Deviation in viscosity where KJ is the Jacobson constant which is temperature dependent, M1, M2, ρ1 and ρ2 are molar masses, densities of pure components 1 and 2,

Results and discussion

The experimental values of u, ρ, and η are found to be nonlinear and can be seen from Table 3. The nonlinear behavior with the concentration of NMP at all the experimental temperatures is considered to be due to the existence of intermolecular interactions between unlike molecules. From Fig. 1 and Table 4, it can be seen that excess molar volume (VmE) values are negative for the systems CHA and CHOL with NMP and decreases with increase in temperature, while for the system CHE with NMP is

Spectral studies

IR studies have been carried for the binary mixtures of CHA, CHOL, and CHE with NMP over the entire composition range. The IR spectrum of pure compounds NMP, CHA and, CHOL at the room temperature shows all the peaks that are available in NIST spectral data. The frequency of band for single bondCO in NMP is observed at 1684.4 cm−1. With the addition of CHA and CHOL to NMP, this band is observed to change in both the frequency and intensity. A red shift is observed in the case CHA and CHOL systems with NMP,

Conclusions

The experimentally determined sound speeds (u), density (ρ), viscosity (η) are found to be non-linear. The excess molar volume (VmE), deviation in isentropic compressibility (Δks), excess free length (LfE) are found to be negative, and deviation in viscosity Δη is found to be positive for the systems CHA and CHOL with NMP at all measured temperatures where as for the system CHE with NMP reverse trend is observed. The variation of Cdouble bondO band frequency, intensity of NMP with the addition of CHA and

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