Density, viscosity and speed of sound of binary liquid mixtures of sulpholane with aliphatic amines at T = K

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1 Indian Journal of Pure & Applied Physics Vol. 47, August 2009, pp Density, viscosity and speed of sound of binary liquid mixtures of sulpholane with aliphatic amines at T = K P Murali Krishna, B Ranjith Kumar, B Sathyanarayana, K Amara Jyothi & N Satyanarayana* Department of Chemistry, Kakatiya University, Warangal * nallani_s@yahoo.com Received 8 December 2008; revised 27 May 2009; accepted 3 July 2009 Experimental data on density, viscosity and speed of sound have been studied for the binary mixtures of sulpholane with diethylamine, n-propylamine, n-butylamine and tert-butylamine at K. Excess molar volume, deviations in viscosity and isentropic compressibility have been computed from this data. The computed quantities have been fitted to the Redlich-Kister equation to derive the binary coefficients and to estimate the standard deviations. All mixtures show negative deviations for excess molar volume, deviations in viscosity and isentropic compressibility. The results have been interpreted on the basis of intermolecular interactions between unlike molecules. Keywords: Excess volumes, Viscosity, Isentropic compressibility, Binary mixtures, Sulpholane, Aliphatic amines 1 Introduction Sulpholane has been extensively used in the petroleum industry for the recovery of aromatic compounds and other organic liquids by liquid extraction methods. It is also used to purify natural gas streams and for fractionation of fatty acids into saturated and unsaturated components and as a reaction solvent for the preparation of aromatic sulphonic acids, pyridines, isocyanates and pharmaceuticals. It can also be involved in the halogen exchange process and polymerization process. Diethylamine is used as a corrosion inhibitor in the production of rubber, resins, dyes and pharmaceuticals. The n-propylamine and n- butylamine are used as raw material for manufacture of drugs such as chlorpromazine and tolbutamide. The tert-butylamine is used as an intermediate in the preparation of rubber accelerations, pesticides, pharmaceuticals, dyes and other organic compounds. The excess molar volumes, deviation in viscosity and deviation in isentropic compressibility of binary mixtures of sulpholane with aliphatic amines have been studied in the present paper. Systematic investigations of the excess thermodynamic properties of binary liquid mixtures have been done to gain information about intermolecular interactions and changes in packing efficiencies with compositions 1-8. As a part of experimental program on the measurement of thermodynamic and transport properties of binary liquid mixtures, densities (ρ), viscosities (η) and speeds of sound (u) have been studied for sulpholane with diethylamine, n-propylamine, n-butylamine and tert-butylamine at K over the whole composition range. The excess molar volume (V E ), deviation in viscosity ( η) and deviation in isentropic compressibility ( κ s ) have been calculated and are fitted to Redlich-Kister type polynomial equation 7 to derive the binary coefficients and to estimate the standard deviation. 2 Experimental Details 2.1 Materials High purity and analytical grade samples of diethylamine LR 99.0% (GC), n-propylamine 98.0% (GC), n-butylamine 99.0% (GC) and tert-butylamine 99.0% (GC) are procured from S.D Fine Chemicals, India. All amines are dried over potassium hydroxide pellets for at least 48 h, distilled twice and the middle fractions were collected 9 and the amines were stored over type 3A 1.5 mm molecular sieves (MERCK) to reduce water content moisture and carbon dioxide gas. The high purity grade sulpholane (99%) furnished by Sigma-Aldrich Chemicals, USA was used without further purification. To minimize the contact of this deliquescent reagent with moist air, the product was kept in sealed bottles in a desiccator. The purities of the samples were confirmed by GLC. The physical properties of pure liquids were compared with literature is compiled in Table 1.

2 KRISHNA et al.: DENSITY, VISCOSITY AND SPEED OF SOUND OF BINARY MIXTURES 577 Table 1 Physical properties of the pure components at K Component ρ 10 3 (kg m 3 ) η 10 3 (m Pas) Expt Lit Expt Lit Sulpholane * Diethylamine n-propylamine n-butylamine tert-butylamine *T = K 2.2 Apparatus and Procedure Binary mixtures were prepared by mass in air tight bottles. The mass measurements were performed on a Dhona 100 DS, India, Single pan analytical balance with a precision of kg. The required properties of the mixture were measured on the same day. The uncertainty in mole fraction was estimated to be less than ± Densities of pure liquids and their mixtures were determined by using a m 3 double arm pycnometer 1. The density values from triplicate replication at the temperature of K were reproducible within ± kg m 3. The uncertainty in density and excess molar volume values were found to be ± kg m 3 and ± m 3 mol 1. Ubbelohde viscometer 10 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 (water conductivity less than ohm 1. cm 1 with ( and ) g. cm 3 as its density at and K respectively, density of benzene ( and ) g. cm 3 at and K, respectively). The detailed experimental procedure of viscometer was discussed earlier 5. Viscosity values (η) of pure liquids and mixtures are calculated using the relation: η = (at-b/t) (1) where a and b are the characteristic constants of the viscometer, ρ is the density and t represents the flow time. The flow time of pure liquids and liquid mixtures were repeated for 5 times. The uncertainty of viscosity was ± m Pas. 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 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 ±0.01 K using a constant temperature bath [INSREF Model IRI-016C, India], and the temperature was monitored with a platinum resistance thermometer with an accuracy of ±0.001 K and an uncertainty of ±0.004 K. 3 Results and Discussion Experimental values of density (ρ), viscosity (η), speed of sound (u), and excess molar volume (V E ), deviation in viscosity ( η) and deviation in isentropic compressibility ( κ s ) for the binary mixtures of sulpholane with DEA, n-pa, n-ba and tert-ba at T = K are given as a function of mole fraction in Table 2. The density values have been used to calculate excess molar volumes (V E ) using the following equation: 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 fraction, molar mass and density of pure components respectively. The deviation in viscosity is calculated using the relation: η = η m (x 1 η 1 + x 2 η 2 ) (3) where η m, η 1, η 2, x 1, and x 2 are viscosity of the liquid mixture, viscosity and mole fractions of pure liquids respectively. The speed of sound u is used to calculate the isentropic compressibility (κ s ) using the equation: κ s = 1/ (u 2.ρ) (4) The deviation from isentropic compressibility ( κ s ) have been evaluated using the equation: κ s =κ s (Φ 1 κ s1 +Φ 2 κ S2 ) (5) where κ s1, κ s2 and κ s are the isentropic compressibility of the pure components and observed isentropic compressibility of liquid mixture respectively. Φ i is

3 578 INDIAN J PURE & APPL PHYS, VOL 47, AUGUST 2009 Table 2 Experimental densities (ρ), viscosities, (η), speed of sound, (u), excess molar volume (V E ), deviation in viscosity ( η) and deviation in isentropic compressibilities ( κ s ) of the binary mixtures of sulpholane (1) with aliphatic amines (2) at K x 1 ρ 10 3 η 10 3 u V E 10 6 η 10 3 κ s kg m 3 m Pas m s 1 m 3 mol 1 m Pas m 2 N 1 Sulpholane (1) + diethylamine (2) Sulpholane (1) + n-propylamine (2) Sulpholane (1) + n-butylamine (2) Sulpholane (1) + tert-butylamine (2)

4 KRISHNA et al.: DENSITY, VISCOSITY AND SPEED OF SOUND OF BINARY MIXTURES 579 the volume fraction of pure components and is calculated from the individual pure molar volumes, V i, with the relation: Φ i =x i V i /(Σx i V i ) (6) The excess properties Y were fitted by the method of non-linear least squares to a Redlich-Kister type polynomial 11 Y = x 1 x 2 Σ A i (x 1 x 2 ) i (7) In each case, the optimum number of coefficients A i was determined from an examination of the variation of standard deviation (σ) as calculated by: σ ( Y) = [Σ ( Y obs Y cal ) / (n m)] ½ (8) where n represents the number of experimental points and m is the number of coefficients. It is found that for the solution of the fifth degree polynomial, the agreement between the experimental values and the calculated ones is satisfactory. The derived parameters (A i ) and the estimated standard deviation (σ) for V E, η and κ s are given in Table 3. Excess molar volume The variation of excess molar volume (V E ) values with the mole fraction (x 1 ) of sulpholane for DEA, n-pa, n-ba and t-ba at K are plotted in Fig. 1. The excess molar volumes for all binary mixtures with sulpholane are negative. The observed V E values are the resultant of physical and chemical forces and they may be broadly recognized as: (i) The breaking of liquid order on mixing with the second component; (ii) Non-specific physical interactions and unfavourable interactions between unlike molecules; (iii) Specific interactions appearing in the mixture between dissimilar molecules by hydrogen bond formation; and (iv) Specific interactions appearing in the mixture between solvent and co-solvent molecules by dipole-dipole. The first two factors contribute for the expansion of volume and the latter two factors contribute to the reduction of the volume. From the V E curves at K shown in Fig. 1, it is clear that the volume reduction factors are dominant over the expansion factors in the present systems. All the amines are associated liquids through H- bonding. When sulpholane is mixed with amines, dissociation of associated liquid structure takes place resulting in an expansion of volume of the mixture. But the observed negative excess molar volume shows that the volume reduction factor plays an important role between unlike molecules. This indicates the formation of hydrogen bond complexes. Thus, the observed negative values of V E indicate the predominance of formation of S=O HN bonds over the rupture of bonds present in pure sulpholane and amines. All amines are moderately polar solvents. Sulpholane is a dipolar aprotic solvent 12, because its high dipole moment (4.8 D) favours dipole-dipole interactions 12 in which negative end of the dipole has exposed. Hence, there will be dipole-dipole interactions between unlike molecules of the four systems, contributing to the reduction in the volume. Table 3 The binary coefficients (A i ) and standard deviations (σ) of sulpholane (1) + aliphatic amines (2) at K Binary system Function Binary coefficients A A 1 A 2 A 3 A 4 Σ Sulpholane + diethylamine V E 10 6 (m 3 mol 1 ) η 10 3 (m Pas) κ s (m 2 N 1 ) Sulpholane + n-propylamine V E 10 6 (m 3 mol 1 ) η 10 3 (m Pas) κ s (m 2 N 1 ) Sulpholane + n-butylamine V E 10 6 (m 3 mol 1 ) η 10 3 (m Pas) κ s (m 2 N 1 ) Sulpholane + tert-butylamine V E 10 6 (m 3 mol 1 ) η 10 3 (m Pas) κ s (m 2 N 1 )

5 580 INDIAN J PURE & APPL PHYS, VOL 47, AUGUST 2009 Fig. 1 Variation of excess molar volumes (V E ) versus mole fraction (x 1 ) of the binary mixtures of sulpholane (1) with, diethylamine (2);, n-propylamine (2);, n-butylamine (2) and, tert-butylamine (2) at the temperature K Fig. 2 Variation of deviation in viscosity ( η) versus mole fraction (x 1 ) of the binary mixtures of sulpholane (1) with, diethylamine (2);, n-propylamine (2);, n-butylamine (2) and, tert-butylamine (2) at the temperature K From the above argument (Fig. 1) it is clear that the specific interactions are present between the mixtures of sulpholane and amines. For instance at equimolar mixture composition, the magnitude of volume contraction are found to increase in the sequence: n-pa < n-ba < tert-ba < DEA The strength of hydrogen bonding interactions increases from primary amine to secondary amine with sulpholane. Deviation in viscosity A perusal of Table 2 shows that the deviations in viscosity ( η) values are negative over the entire composition range for all the binary liquid mixtures at K. The negative η values at equimolar concentration of sulpholane and amines vary as per the sequence tert-ba < n-pa < n-ba < DEA A correlation between the sign of η and V E has been observed for a binary system, η being positive where V E is negative or vice-versa 13. Figures 1 and 2 clearly indicate that the isotherms of V E and η do not go by the general statement. For such systems, Rastogi et al. 14 suggested that the observed excess property is a combination of an interaction and a noninteraction part. Thus: Y (observed) = Y (interaction) + Y size effect), Fig. 3 Variation of deviation in isentropic compressibility ( κ s ) versus volume fraction (Φ 1 ) of the binary mixtures sulpholane (1) with, diethylamine (2);, n-propylamine (2);, n-butylamine (2) and, tert-butylamine (2) at the temperature K where Y refers to the excess or deviation in the property. The non-interaction part in the form of the size effect can be comparable to the interaction part and may be sufficient to reverse the trend set by the latter. Based on this theory, the observed incongruity may be accredited to the size effect. Deviation in isentropic compressibility The variation of κ s with composition of mixture (Φ 1 of sulpholane) is shown in Fig. 3. From the isotherms it is seen that κ s values are negative for all the systems

6 KRISHNA et al.: DENSITY, VISCOSITY AND SPEED OF SOUND OF BINARY MIXTURES 581 studied. The algebric values of κ s for the four systems at equimolar compositions are in the order: n-pa < n-ba < tert-ba < DEA Sulpholane and amines are highly polar in nature. The behaviour of mixtures can be explained in terms of (i) physical forces dispersion (ii) chemical forces dipole-dipole interactions and hydrogen boding formation. The former factor increases the intermolecular path lengths, as described by Jacobson 15. This in turn causes positive deviation in compressibility. On the other hand, the latter factor decreases the inter-molecular path lengths leading to a negative deviation in compressibility. The actual values depend upon the relative strengths of the two opposing effects. The observed negative values of κ s for these mixtures imply that the specific interactions dominate over the dispersive interactions between unlike molecules. Usually the behaviour of V E and κ s are similar in nature. This tendency is also found in the present study, showing the same sign and same order as that of V E. 4 Conclusions The experimental values of density, viscosity and speed of sound for the binary mixtures of sulpholane with diethylamine, n-propylamine, n-butylamine and tert-butylamine at K and different compositions are measured. From these data, several thermodynamic excess functions have been calculated and correlated using the Redlich-Kister polynomial equation. The sign and magnitude of these quantities have been discussed in terms of hydrogen bonding and dipole-dipole interactions between the mixing components. In the entire composition range excess molar volume, deviation in viscosity and deviation in isentropic compressibility are negative for all binary mixtures. References 1 Sathyanarayana B, Ranjith Kumar B, Savitha Jyostna T & Satyanarayana N, J Chem Thermodyn, 39 (2007) Satyanarayana N, Satyanarayana B & Savitha Jyostna T, J Chem Eng Data, 52 (2007) Savitha Jyostna T & Satyanarayana T, J Chem Thermodyn, 38 (2006) Sathyanarayana B, Savitha Jyostna T & Satyanarayana N, Indian J Pure & Appl Phys, 44 (2006) Savitha Jyostna T & Satyanarayana N, Indian J Chem, 44 (2005) Ranjith Kumar B, Murali Krishna P, Sathyanarayana B, Savitha Jyostna T & Satyanarayana N, Indian J Chem, 47A (2008) Ranjith Kumar B, Murali Krishna P, Satyanarayana B & Satyanarayana N, J Chem Eng Data, 53 (2008) Satyanarayana B, Ranjith Kumar B, Murali Krishna P & Satyanarayana N, J Chem Eng Data, 40 (2008) Kalgud M V & Patil K J, J Phys Chem, 80 (1976) Nikam P S, Shirsat L N & Hasan M, J Chem Eng Data, 43 (1998) Redlich O & Kister A T, Ind Eng Chem, 40 (1948) Sacco A & Jannelli L, J Chem Thermodyn, 4 (1972) Fort R J & Moore W R, Trans Faraday Soc, 62 (1966) Rastogi R P, Nath J & Misra J, J Phys Chem, 71 (1967) Jacobson B, J Chem Phys, 20 (1952) Lampreia I M S, Dias F A & Mendonca A F S S, J Chem Thermodyn, 36 (2004) Pal A & Bharadwaj R K, J Chem Eng Data, 46 (2001) Subha M C S, Swamy G N, Bhai M E & Rao S V K, Indian J Chem, 43A (2004) Riddick J A, Bunger W B & Sakano T K, Organic solvents, physical properties and methods of purification, Techniques of Chemistry, 4 th Edn, vol. II (Wiley-Interscience, New York), 1986, p 7.