Volumetric and transport properties of binary liquid mixtures of aromatic hydrocarbons with N-methylacetamide at K

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1 Indian Journal of Pure & Applied Physics Vol. 47, July 2009, pp Volumetric and transport properties of binary liquid mixtures of aromatic hydrocarbons with N-methylacetamide at K B Ranjith Kumar, B Satyanarayana, S Asra Banu, K Amara Jyothi, T Savitha Jyostna & N Satyanarayana* Department of Chemistry, Kakatiya University, Warangal , Andhra Pradesh * nallani_s@yahoo.com Received 11 November 2008; revised 12 March 2009; accepted 25 May 2009 Experimental data on density, viscosity and speed of sound values at K are presented for the binary mixtures of N-methylacetamide with benzene, toluene, mesitylene and phenylacetonitrile. From these experimental data, excess molar volumes, deviations in viscosity and isentropic compressibility of aromatic hydrocarbons with N-methylacetamide have been calculated. The computed values have been fitted to Redlich-Kister polynomial equation using multiparametric non-linear regression analysis to estimate the coefficients and standard errors. The variations in the calculated excess quantities for these mixtures have been studied in terms of molecular interactions between the component liquids and the effects of methyl and cyanomethylene substitution on benzene ring. Keywords: Excess volumes, Viscosity deviations, Isentropic compressibility deviations, Binary mixtures, N-methylacetamide, Aromatic hydrocarbons 1 Introduction The study of the thermodynamic and transport properties of binary mixtures is useful for many purposes, one of which is to obtain information on molecular features of the studied mixtures 1-4. On the other hand, hydrocarbons are among the most important chemicals used in hydrocarbon processing industries. The characterization of the mixtures through their thermodynamic and transport properties is important from the fundamental viewpoint to understand their mixing behaviour (molecular interactions) as well as in practical applications such as in petrochemical industries. In continuation of our previous research on the study of binary organic liquid mixtures 5-12, the binary mixtures of N- methylacetamide + substituted monocyclic aromatic liquids has been studied in the present paper. In recent years, the thermodynamic and transport properties of binary liquid mixtures containing aliphatic, cyclic hydrocarbons and esters with aromatic hydrocarbons have been investigated. However, in the present study, the molecular interactions of four monocyclic substituted aromatics with N-methylacetamide have been investigated. When such liquids are mixed with N- methylacetamide their mixing properties vary depending upon the substitution of benzene moiety. In an effort to investigate this effect, we have measured density (ρ), viscosity (η) and speed of sound u of mixtures of N-methylacetamide (NMA) + benzene (BEN), + toluene (TOL), + mesitylene (MES) and + phenylacetonitrile (PAN) over the entire range of mole fraction at a temperature of K. From these data, excess molar volumes (V E ), deviations in viscosity (Δη) and deviations in isentropic compressibility (Δκ s ) have been computed. These results have been fitted to Redlich-Kister polynomial equation 17 to derive the binary coefficients and estimate the standard deviations between experimental and calculated data. Results have been used to explain the nature of molecular interactions between mixing components. The strength of specific and non-specific interactions between components of the binary mixtures has been examined in terms of the differences of the component molecules as well as the nature of interacting groups of benzene. 2 Experimental Details 2.1 Materials High purity and analytical grade benzene with purity of 99.7% (GLC) and phenylacetonitrile 98% is procured from S D Fine Chemicals Ltd; India and used after a single distillation. Toluene analytical grade with purity of 99.5% (GC) is purchased from Merck, India, and N-methylacetamide 99% (GC) and mesitylene 98% are purchased from Sigma-Aldrich Chemicals Pvt Ltd, Germany. These samples are used without further purification.

2 512 INDIAN J PURE & APPL PHYS, VOL 47, JULY Apparatus and Procedure Binary mixtures are prepared by mass in air tight bottles. The mass measurements were performed on a Dhona 100 DS, India, Single pan analytical balance with a resolution of kg. The required properties of the mixture are measured on the same day. The uncertainty in mole fraction is estimated to be less than ± The densities of pure liquids and their mixtures were determined by using double arm pycnometer of m 3 as described in our previous paper 9. The density values from triplicate replication at temperature K were reproducible within ± g cm 3. The uncertainties in density and excess molar volume values are found to be ± g cm - 3 and ± cm 3 mol 1 (Table 1). An Ubbelohde viscometer 18 having a capacity of about 15 ml and the capillary having a length of about 90 mm and 0.5 mm internal diameter has been used to measure the flow times of pure liquids and liquid mixtures and it was calibrated with benzene and doubly distilled water. The detailed experimental procedure with the viscometer was discussed in our previous paper 9. Viscosity values (η) of pure liquids and mixtures are calculated using the relation: η = (at b/t) ρ (1) where a and b are the characteristic constants of the viscometer; ρ is the density and t represents the flow time. The flow times of pure liquids and liquid mixtures are repeated for 5 times. The uncertainty of viscosity was ± m Pas. The speed of sound was determined by using an ultrasonic interferometer [Model M-82, Mittal Enterprises, India], working at 2MHz frequency. The working principle used in the measurement of speed of sound through medium was based on the accurate determination of the wavelength of ultrasonic waves of known frequency produced by quartz crystal in the measuring cell 10,19. The temperature of the solution Table 1 Physical properties of pure components at K Components ρ 10 3 /g cm 3 η 10 3 /m Pas Exptl. Lit. Exptl. Lit N-methylacetamide Benzene * * Toluene * Mesitylene * Phenylacetonitrile * a * Values at K. a Handbook of Fine Chemicals, Sigma-Aldrich, India was controlled by circulating water at a desired temperature through the jacket of double-walled cell. The speed of sound was measured with relative uncertainty of ±0.3%. In all the property measurements, the temperature was controlled within ±0.01K using a constant temperature bath [INSREF Model IRI 016C, India], and the temperature was monitored with a platinum resistance thermometer with an accuracy of ±0.001K and an uncertainty of ±0.004K. 3 Results and Discussion The values of excess molar volumes V E, deviation in viscosity Δη and deviations in isentropic compressibility Δκ s for the binary mixtures of N-methylacetamide with benzene, toluene, mesitylene and phenylacetonitrile at K along with the mole fraction are presented in Table 2. The excess molar volumes V E have been evaluated from density using V E = (x 1 M 1 +x 2 M 2 )/ ρ m (x 1 M 1 / ρ 1 +x 2 M 2 /ρ 2 ) (2) where ρ m is the density of the mixture; x 1, M 1, ρ 1 and x 2, M 2 and ρ 2 are the mole fractions, molecular weights and densities of pure components 1 and 2, respectively. The deviation in viscosity is calculated using the relation : Δη = η m (x 1 η 1 + x 2 η 2 ) (3) where η m, η 1 and η 2 are viscosities of the liquid mixture and of the pure components 1 and 2, respectively; x 1 and x 2 are the mole fractions of the pure components 1 and 2 in the liquid state. The deviation in isentropic compressibility has been evaluated using the equation: Δκ s = κ s (Φ 1 κ s1 + Φ 2 κ s2 ) (4) where Φ i is the volume fraction of pure components and is calculated from the individual pure molar volumes, V i, using the relation: Φ i =x i V i /(Σx i V i ) (5) and κ s1, κ s2 and κ s were the isentropic compressibility of the pure components and observed isentropic compressibility of liquid mixtures, respectively. The excess or deviation properties ΔY are fitted by the method of non-linear least-squares to the fourthorder Redlich-Kister type polynomial 17.

3 KUMAR et al.: VOLUMETRIC AND TRANSPORT PROPERTIES OF BINARY LIQUID MIXTURES 513 Table 2 Densities, (ρ), viscosities, (η), speed of sound, (u), excess molar volume, (V E ), deviation in viscosity, (Δη), and deviation in isentropic compressibilities, (Δκ s ) of the binary mixtures of N-methylacetamide (1) +aromatic hydrocarbon (2) at K. x 1 ρ 10 3 η 10 3 u V E 10 6 Δη 10 3 Δκ s g cm 3 m Pas m s 1 m 3 mol 1 m Pas m 2 N 1 Benzene (2) Toluene (2) Mesitylene (2) Phenylacetonitrile (2)

4 514 INDIAN J PURE & APPL PHYS, VOL 47, JULY 2009 Table 3 Binary coefficients (A i ) and standard deviations (σ) of N-methylacetamide (1) +aromatic hydrocarbons (2) at K Binary system Function A 0 A 1 A 2 A 3 A 4 σ N-methylacetamide (1)+ V E 10 6 (m 3 mol 1 ) Benzene (2) Δη 10 3 (m Pas) Δκ s (m 2 N 1 ) Toluene (2) V E 10 6 (m 3 mol 1 ) Δη 10 3 (m Pas) Δκ s (m 2 N 1 ) Mesitylene (2) V E 10 6 (m 3 mol 1 ) Δη 10 3 (m Pas) Δκ s (m 2 N 1 ) Phenylacetonitrile (2) V E 10 6 (m 3 mol 1 ) Δη 10 3 (m Pas) Δκ s (m 2 N 1 ) ΔY = x 1 x 2 ΣA i ( x 1 x 2 ) i...(6) where A 0, A 1, and A 2 are adjustable binary coefficients. The coefficients A i were estimated using multi-parametric regression analysis based on a leastsquares method. The number of A i parameters was optimized using F-test and is found to be five (m=5). In each case, the optimum number of coefficients A i is determined from an examination of the variation of standard deviation (σ) as calculated by : σ (Y E ) = [Σ(ΔY obs ΔY cal ) 2 /(n m)] 1/2 (7) where n represents the number of experimental points and m is the number of coefficients used in fitting the data. The estimated values of coefficients A i and standard deviations σ (V E, Δη, and Δκ s ) of the fit are presented in Table 3. Excess molar volume Plots of excess molar volumes V E against x 1 at K for all binary mixtures are shown in Fig. 1. The values of V E for the mixtures of N-methylacetamide +benzene, +toluene, +phenylacetonitrile are negative whereas for the mixtures of N-methylacetamide +mesitylene are positive. For instance, at equimolar mixture compositions, V E results vary as per the sequence: TOL > BEN > PAN > MES with increasing molar volumes of liquids. The V E values are the result of contributions from several opposing effects. These may be divided arbitrarily into three types, namely chemical, physical and structural (geometrical) characteristics of the Fig. 1 Variation of excess molar volumes, (V E ), versus mole fraction (x 1 ) of the binary mixtures of N-methylacetamide (1) with, benzene (2);, toluene (2);, mesitylene (2) and, phenylacetonitrile (2) at the temperature K liquids. Physical contributions (dispersion forces), which are non-specific interactions between the real species present in the mixture; contribute a positive term to V E ; chemical or specific intermolecular interactions (structural effects) which result in a volume decrease. This effect contributes negative values to V E. In the present study, negative values of V E for N-methylacetamide + benzene, + toluene systems indicate π-electron donor-acceptor type specific interactions between unlike molecules 20. The strong negative magnitude of V E of toluene than benzene can be interpreted as a consequence of the strong attractions appearing between π-electrons of toluene and the lone pair of electrons in the amide NH group due to the introduction of CH 3 group on the benzene ring, π-electron donating capacity

5 KUMAR et al.: VOLUMETRIC AND TRANSPORT PROPERTIES OF BINARY LIQUID MIXTURES 515 Fig. 2 Variation of deviations in viscosity, (Δη), versus mole fraction (x 1 ) of the binary mixtures of N-methylacetamide (1) with, benzene (2);, toluene (2);, mesitylene (2) and, phenylacetonitrile (2) at the temperature K increases, thereby increasing the attractive interactions between the two components. In the case of N-methylacetamide + phenylacetonitrile system; the less negative values of V E than benzene may be attributed to formation of new molecular complexes through n-π interactions. The positive V E values for N-methylacetamide + mesitylene system arises due to steric hindrance of methyl groups 21 (dispersion forces). Viscosity deviation The plots of deviations in viscosity versus mole fraction (Δη versus x 1 ) at K for N-methylacetamide + benzene, + toluene, + mesitylene and + phenylacetonitrile are shown in Fig. 2. The negative values of Δη are seen for all the mixtures over entire mole fraction range. Large negative deviation is observed for N-methylacetamide + toluene and less negative deviation is observed for N-methylacetamide +phenylacetonitrile than benzene and mesitylene. Thus, Δη values do not seem to follow any systematic trend with increasing molar mass or volume of the substituted benzenes. It is observed that negative values of Δη for all the systems vary as per the sequence: TOL > BEN > MES > PAN Figures 1 and 2 show that the plots of V E and Δη are not according to general statement of Fort 22. This observation can explain that the observed property is a combined effect of an interaction and noninteraction part of the molecules. The non-interaction part is in the form of size and shape of the component molecules 23. Deviation in isentropic compressibility The results of Δκ s versus Φ 1 (volume fraction of NMA) at K for mixtures of (N-methylacetamide + Fig. 3 Variation of deviations in isentropic compressibility, ( κ s ), versus volume fraction (Φ 1 ) of the binary mixtures of N methylacetamide (1) with, benzene (2);, toluene (2);, mesitylene (2) and, phenylacetonitrile (2) at the temperature K benzene, + toluene, + mesitylene and + phenylacetonitrile are shown in Fig. 3. For the mixtures of (N-methyl-acetamide +benzene, +toluene and +mesitylene), a positive deviation in Δκ s is observed whereas for N-methylacetamide + phenyl-acetonitrile the values are negative. However, the Δκ s values decrease in the order for TOL > BEN > MES, while the mixture with PAN shows very large negative deviation. The same sign for V E and Δκ s was observed for a number of binary solvent systems. But it is reverse in case of benzene and toluene systems which is quite obvious in the literature In all the plots in Fig. 3, points represent the quantities calculated from Eqs 2-4 using the measured values of ρ, η and u, while smooth curves are drawn from the best-fit values calculated from the Redlich- Kister equation. 4 Conclusions In this paper, the densities, viscosities and speed of sound at K over the entire range of composition of N-methylacetamide + benzene, + toluene, + mesitylene or + phenylacetonitrile mixtures have been measured. From these measured physical property data, excess molar volumes, deviations in viscosity and isentropic compressibility have been calculated and correlated by a Redlich- Kister type polynomial equation to derive the coefficients and standard deviation. The results are interpreted in terms of molecular interactions between the components. References 1 Osborne C G & Morcom K W, J Chem Thermodyn, 13 (1981) 235.

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