Molecular Interactions of Aniline in Toluene + Iso-Butanol System

Indian Journal of Pure & Applied Physics Vol. 49, December 2011, pp. 803-808

Molecular interactions of aniline in toluene + iso-butanol system

G Mahendran & L Palaniappan* Department of Physics, Arignar Anna Government Arts College, Namakkal, Tamil Nadu, India *Department of Physics (DDE), Annamalai University, Annamalainagar 608 002, Tamil Nadu, India *E-mail: [email protected] Received8 February2011; revised 2 September 2011; accepted 17 October 2011

The separation efficiency of aniline by destructing the azeotropic formation in the binary toluene + iso-butanol has been analysed using ultrasonic techniques. Ultrasonic velocity, density and viscosity values have been measured at 303 K in the ternary system of aniline + toluene + iso-butanol and thermo dynamical approach is applied to evaluate the molar volume, adiabatic compressibility, internal pressure, molar cohesive energy and their excess values. Results are interpreted in terms of molecular interactions between the components of the mixtures and compared with molecular interaction parameter that can highlight the role of aniline in the azeotropic destruction of the chosen binary. Observed excess values lend further support to the interactions found in the binary and ternary systems. The dipole type interaction existing between aniline and iso-butanol is found to be the predominant factor for destructing the azeotrope formation. Keywords: Azeotropes, Binary mixtures, Ternary mixtures, Velocity, Density, Molecular interactions

1 Introduction ultrasonic techniques. As alcohols are invariably Velocity of sound waves in a medium is found as a component in petrochemical azeotropes, fundamentally related to the binding forces between iso -butanol is chosen for the present study. Toluene is the atoms or the molecules. The variations of taken as second azeotropic component because of its ultrasonic velocity and related parameters throw some importance in the separation process of petrochemical light on the intermolecular interactions and the intermediates. Thus, the present work forms a structural changes associated with the liquid mixtures continuation of our effort in analyzing the role of having weakly interacting components 1-3 as well as aniline in offering intermolecular interactions with the strongly interacting components 4-6. As these components that can deform iso -butanol-toluene interactions form the basis for the related process or azeotropes. phenomenon, the observed interactions can be utilized The azeotropic components are chosen for the to offer explanation for the macroscopic variations present work, are the toluene (boiling point 384 K), a found in the liquid mixtures. One such application can weak polar and iso-butanol (boiling point 381 K), a be found in distillation process industries to explain strong polar. In the present work, ultrasonic the destruction of binary azeotropes by the addition of techniques have been employed for the evaluation of a suitable solvent or entrainer 7-9. In general, aniline molecular interaction in the binary and ternary seems to be the best among the various extractive mixtures containing aniline, iso -butanol and toluene at solvents due to its high boiling point (457.4 K) and 303 K in order to explain the inherent nature of structural features. Thus, liquid mixtures with aniline aniline that aids in azeotropic destruction. as one component are indispensable for the industrial rectification column to avoid the formation of 2 Experimental Details azeotropes. The mixtures of various concentrations in mole The ability of aniline in breaking the various binary fraction by weight were prepared by taking purified azeotropes has been studied by many researchers AR grade samples at 303 K. The purification was using different techniques 7-10 . The same purpose was done as per the standard procedures 12 and the purity met out using ultrasonic techniques in our previous was checked by comparing the density with those work for the 1-propanol-toluene azeotropes 10 . Apart reported in literature 13 and found to be closer to first from aniline, the ability of pyridine in breaking the decimal. The ultrasonic velocities in liquid mixtures benzene-2-butanol azeotropes has also been studied have been measured using an ultrasonic by the authors in their earlier work 11 employing interferometer (Mittal type) working at 2 MHz 804 INDIAN J PURE & APPL PHYS, VOL 49, DECEMBER 2011 frequency with an accuracy of ± 0.1 ms −1. The density weight of i th component and AE stands for excess and viscosity are measured using a Pycknometer and property of any given parameter, Aexp is the an Ostwald’s viscometer, respectively with an experimental value and Aid is the respective ideal 5 –2 accuracy of 3 parts in 10 for density and 0.001 Nsm value. Uimr stands for the ultrasonic velocity predicted for viscosity. Using the measured data, the acoustical by means of ideal mixing relation 18 . The useful parameters such as molar volume ( V), adiabatic standard values of the component liquids are taken 19-21 compressibility ( β), internal pressure ( πi) molar from the literature and presented in Table 1. cohesive energy (MCE) and their excess parameters have been calculated using the following standard 3 Results and Discussion thermodynamical expressions 14-17 . Though many The measured values of density ( ρ), sound velocity researchers in India have used the traditional (U) and viscosity ( η) are presented in Table 2. The Newton’s formula for the calculation of adiabatic calculated values of molar volume ( V), adiabatic 2 −1 compressibility (= ( ρu ) ), it was strongly proved that compressibility ( β), internal pressure ( πi), the molar the formula is lack of molar counterpart and hence, cohesive energy (MCE) and the molecular interaction invalid 14-16 . Thus, the calculations performed in the parameter (MIP) for the binary and ternary mixtures present work consider all the quantities in their molar containing aniline, toluene and iso-butanol are nature by adopting the latest equations. presented in the Table 3. The perusal of Table 2 indicates that the sound M eff velocity and density in all the binary and ternary V = … (1) systems increase non-linearly with the mole fraction ρmix of first component. This trend suggests the possibility 2 αidV id of intermolecular interactions between the β=β − T … (2) 22 T id Cp components of the systems . The increasing trend of id density reveals that the addition of first component

1 2 2 makes the systems to be more compact, thereby kη   ρ 3    … (3) πi = bRT   7 revealing the attractive type interaction between the U  M 6  eff  components. As the medium becomes more and more compact, velocity also increases as is observed in all MCE = πi V … (4) the systems. The coefficient of viscosity also shows AE = A − A … (5) an increasing trend in all the systems except toluene + exp id iso-butanol system. As toluene molecules are heavier A= ∑ x A … (6) than alcohol, density and hence, sound velocity id ii increase with increase in mole fraction of toluene. For 2 2 the same reason, the frictional forces and hence, the and MIP=U exp /U imr ) – 1 … (7) relative velocity between the layers will be feeble and this leads to a net reduction of η. Thus, whether the In Eqs (1-7), βTid is the ideal isothermal components are polar or weak polar favourable compressibility and αid is the ideal thermal expansion coefficient which are non-Gibbsian parameters and interaction exists in all the system to make that its hence, are volume fraction additive whereas the ideal compact is evident. molar volume ( V ) and the ideal specific heat It is interesting to note the trend of the calculated id parameters in Table 3, especially the molar volume, capacity at constant pressure ( Cp) are Gibbsian parameters and hence, mole fraction additive. The Table 1—Standard values of dipole moment ( D), density ( ρ), calculated molar volume values are used to change ultrasonic velocity (U), viscosity ( η), isothermal compressibility the mole fraction to corresponding volume fraction of (βT), thermal expansibility ( α) and specific heat capacity ( Cp) at the components. Further, b is the cubical pacing constant pressure of the experimental liquids at 303 K fraction, R the universal gas constant, T the absolute 3 12 3 Liquid D ρ U η×10 βT× 10 α×10 Cp –3 –1 temperature and kT is the temperature dependent kgm ms Nsm −2 Pa −1 K−1 kJkg −1K−1 constant having a value 201.1209×10 –8 in MKS system, k (= 4.28 ×10 9) is the temperature independent Aniline 1.131010.91614.0 3.036 453 0.81 2.167 constant, η is the coefficient of viscosity, Meff Σximi Toluene 0.37 857.8 1287.2 0.526 681.7 1.07 1.70 where x is the mole fraction and m is the molecular iso-Butanol 1.66 791.8 1157.5 2.580 1026 0.948 2.44 MAHENDRAN & PALANIAPPAN: MOLECULAR INTERACTIONS OF ANILINE 805

Table 2—Measured values in binary and ternary systems at interaction depends not only on the polarity or 303 K structure but some more factors such as functional Mole fraction ρ U η×10 3 group. However, it is to be noted that the magnitude –3 –1 -2 x1 kgm ms Nsm of molar volume is small as compared with the other Aniline + Toluene two binaries, so that the medium is much more 0.0000 857.8 1287.2 0.526 condensed in this system only. 0.0998 870.3 1324.3 0.801 0.1992 884.6 1355.4 1.075 As regards the ternary molar volume trend, in 0.3003 899.8 1388.6 1.292 general, it is decreasing and shows a minimum value 0.3997 916.2 1422.5 1.501 0.5002 932.5 1454.6 1.822 at 0.6 mole fraction of aniline; again suggest that 0.6013 947.2 1480.2 2.031 structural formation still exists. Comparing the 0.7004 963.5 1512.3 2.341 magnitudes, it can easily be predicted that the ternary 0.8002 981.2 1548.6 2.553 compactness is better than that in aniline + toluene 0.9003 995.4 1585.5 2.783 and toluene + iso-butanol binaries but worse than 1.0000 1010.9 1614.0 3.036 Aniline + iso-Butanol aniline + iso-butanol system. 0.0000 791.8 1157.5 2.580 A monotonous decreasing nature of adiabatic 0.0996 828.6 1205.3 2.602 compressibility is observed with increase in the mole 0.2000 845.3 1249.6 2.644 0.2990 866.2 1296.5 2.692 fraction of first component in all the systems which 0.4001 882.5 1340.3 2.743 assure that all systems show structural compactness. 0.5001 906.5 1386.2 2.785 However, the degree of compactness differs from one 0.5997 924.3 1432.6 2.832 system to other as is seen from the respective 0.7006 945.7 1478.5 2.885 0.7985 966.2 1512.8 2.911 magnitude variations. Compressibility is the measure 0.8996 985.3 1560.3 2.950 of the ease with which a system can easily be 1.0000 1010.9 1614.0 3.036 compressed. i.e., the larger the compressibility the Toluene + iso-Butanol easier it can be compressed because of more free 0.0000 791.8 1157.5 2.580 space between the components 23 . Hence, the 0.1001 797.5 1170.2 2.374 0.2008 804.2 1183.6 2.165 observation of binary systems reveals that toluene + 0.2997 810.0 1196.1 1.961 iso-butanol and aniline + iso-butanol systems are 0.3995 816.2 1209.5 1.771 highly compressible whereas aniline + toluene system 0.5004 822.5 1222.2 1.575 is less compressible. Considering the two binary 0.6003 828.6 1235.6 1.362 0.7009 835.7 1248.4 1.158 systems of toluene, it is evident that the aniline – 0.7992 842.4 1261.5 0.932 toluene separation is smaller than the toluene – iso- 0.9004 849.5 1274.8 0.736 butanol separation. This means that toluene, if placed 1.0000 857.8 1287.2 0.526 in a mixed environment of aniline and iso-butanol, is x1 x3 Aniline + Toluene + iso-Butanol likely to interact more with aniline. In general, 0.0000 0.7000 810.1 1196.2 1.962 0.0961 0.6051 832.4 1239.6 2.002 alcohol molecules have both hydrophilic and 0.2003 0.5007 853.6 1284.5 2.063 hydrophobic groups, the later being denser than the 0.3003 0.3998 876.2 1325.6 2.115 former. The hydrophilic –OH group that helps it 0.4008 0.2991 899.6 1368.5 2.163 dissolve polar molecules and ionic substances 0.5018 0.1987 921.8 1412.6 2.210 whereas the short, hydrophobic hydrocarbon chain 0.6011 0.0994 944.6 1460.1 2.265 24 0.6996 0.0000 963.5 1512.3 2.342 can attract non-polar molecules . Hence, iso-butanol in spite of having two active groups and more polar reflect the specific variation with components of the than aniline, their hydrophilic part have no favourable mixture. The molar volume shows a continuous counterpart to interact in the mixture of toluene decrease in aniline + toluene system, a continuous whereas the hydrophobic part remains less interactive increase in toluene + iso-butanol system but it highly in aniline mixture. Thus, the trend shown by the fluctuates around 92 m 3mol −1 in aniline + iso-butanol mixtures of iso-butanol always make it to be highly system. Such variations predict that in the systems of compressible or higher separation between the aniline + toluene and toluene + iso-butanol, though components followed by increasing molar volume. toluene is weak polar, the addition of polar molecule This may be attributed to the inherent associative forms some structural pattern. But if both components nature of the alcohol and in particular the excellent are polar as in aniline + iso-butanol, the degree of salvation nature of iso-butanol. As the system is 806 INDIAN J PURE & APPL PHYS, VOL 49, DECEMBER 2011

Table 3 — Calculated values in binary and ternary systems at 303 K

6 10 −8 Mole fraction V×10 β× 10 πi×10 MCE MIP 3 −1 −1 −1 x1 m mol Pa Pa KJmol Aniline + Toluene 0.0000 107.4143 6.5978 3.0705 3.2981 0.000 0.0998 105.9416 6.4168 3.7689 3.9933 0.020 0.1992 104.3703 6.2298 4.3560 4.5465 0.029 0.3003 102.7890 6.0327 4.7621 4.8953 0.039 0.3997 101.0353 5.8313 5.1276 5.1812 0.046 0.5002 99.3749 5.6201 5.6458 5.6113 0.047 0.6013 97.8886 5.3990 5.9670 5.8416 0.034 0.7004 96.4098 5.1760 6.3979 6.1688 0.031 0.8002 94.7046 4.9408 6.6790 6.3250 0.027 0.9003 93.5077 4.6985 6.9447 6.4947 0.022 1.0000 92.1159 4.4455 7.2597 6.6872 0.000 Aniline + iso-Butanol 0.0000 93.5842 10.1556 8.7661 8.2049 0.000 0.0996 91.7321 9.5950 8.6323 7.9197 0.047 0.2000 92.1526 9.0279 8.4162 7.7565 0.080 0.2990 92.0174 8.4653 8.2502 7.5926 0.110 0.4001 92.5891 7.8927 8.0563 7.4597 0.129 0.5001 92.2523 7.3232 7.9094 7.2977 0.141 0.5997 92.5092 6.7530 7.7445 7.1648 0.141 0.7006 92.4530 6.1745 7.6122 7.0382 0.129 0.7985 92.4033 5.6103 7.4833 6.9152 0.087 0.8996 92.5712 5.0270 7.3299 6.7854 0.048 1.0000 92.1159 4.4455 7.2597 6.6876 0.000 Toluene + iso-Butanol 0.0000 93.5842 10.1556 8.7661 8.2042 0.000 0.1001 95.2540 9.7580 8.1507 7.7643 0.012 0.2008 96.6549 9.3682 7.5661 7.3135 0.020 0.2997 98.1442 8.9955 7.0028 6.8731 0.026 0.3995 99.5711 8.6283 6.4732 6.4451 0.030 0.5004 101.1836 8.2700 5.9297 6.0003 0.035 0.6003 102.4438 7.9172 5.3792 5.5114 0.031 0.7009 103.7806 7.5746 4.8342 5.0174 0.028 0.7992 104.9459 7.2430 4.2369 4.4462 0.019 0.9004 106.3312 6.9158 3.6692 3.9028 0.013 1.0000 107.4143 6.5978 3.0705 3.2985 0.000 x1 x3 Aniline + Toluene + iso-Butanol 0.0000 0.7000 98.1508 9.0977 7.0324 6.9023 0.026 0.0961 0.6051 97.6912 8.5534 6.9220 6.7622 0.056 0.2003 0.5007 97.5910 7.9579 6.8246 6.6603 0.076 0.3003 0.3998 97.2631 7.3840 6.7402 6.5564 0.083 0.4008 0.2991 96.8620 6.8096 6.6528 6.4441 0.082 0.5018 0.1987 96.6014 6.2352 6.5592 6.3362 0.072 0.6011 0.0994 96.4692 5.6684 6.4781 6.2367 0.055 0.6996 0.000 96.3421 5.1030 6.4031 6.1691 0.030 replaced by more polar molecules, depending on the can interact with the other two components if the other component of the system, either hydrophobic or components behave as electron-donors. In this case, hydrophilic interaction of increasing magnitude arises the hydrophobic group exhibits attractive type and hence, adiabatic compressibility decreases 25,26 . interactions and the hydrophilic shows repulsive type Toluene and aniline being aromatic, and aniline whereas repulsive interactions exist in between the with amino group, behaves as electron donors. two electron-donors, as a net effect the ternary system Though the amino group is comparatively a strong experiences a larger compressibility. In case if aniline electron-donor, the H atoms in the NH 2 group can also behaves as electron-acceptor then it seems that donor- play the role of electron-acceptor centres 27 . Hence, acceptor complexation of the two solutes exist in the butanol with its hydrophobic and hydrophilic groups alcohol medium wherein all are attractive type MAHENDRAN & PALANIAPPAN: MOLECULAR INTERACTIONS OF ANILINE 807 interactions that lead to a comparatively lower compressibility. The perusal of Table 3 further shows that ternary compressibility values are larger than that of aniline + toluene system. This reveals that aniline in the ternary system behaves as electron acceptor rather than electron donor. Thus, it supports the dominating dipole or induced dipole type interactions of aniline with toluene rather than the inherent dispersive type of toluene in the ternary system. As dipole type Fig. 1 — Mole fraction versus excess molar volume at 303 K interactions are stronger in magnitude than the other types, it is quite evident that the addition of aniline to the binary toluene + iso-butanol makes aniline to have strong interactions with toluene, not to such extent with iso-butanol This happens at all mole fractions of aniline, thus conveying that aniline can combine with polar butanol as well as with weak polar toluene. The measure of the net adhesive/cohesive forces between the components of the mixture is reflected by the values of the internal pressure. Aniline + toluene system shows an increasing trend whereas all other Fig. 2 — Mole fraction versus excess adiabatic compressibility systems record a decreasing trend with the mole at 303 K fraction of the first component. This ensures that the existing dipole-induced dipole type interactions of aniline – toluene system have generated appreciable cohesion between the components. This is supposed to facilitate the destruction of toluene-iso-butanol azeotropes in which the cohesion is comparatively less. The same behaviour is reflected in molar cohesive energy in all the systems. As MCE connotes the free energy state of liquid system in whatever state of aggregation, the increasing trend of MCE always accounts for the enhancement of the structure forming Fig. 3 — Mole fraction versus excess internal pressure at 303 K tendency of the solvent molecules as reported by Poonam Sharma et al.17 and Sanaria et al.28 in different liquid mixtures. All the systems considered are having dipoles and hence, expected to exhibit appreciable interaction. As these interactions highly depend on the mole fraction of polar molecules 29 , all the systems invariably exhibit peak interaction at equimolar mole fraction. This is exactly shown by the trend of molecular interaction Fig. 4 — Mole fraction versus excess molar cohesive energy at 303 K parameter (MIP) calculated by ideal mixing relation. The respective excess parameters have been iso-butanol system clearly confirms the existence of calculated and are shown in Figs 1-4. The deviation strong interactions in it. Thus, all the parameters from ideality is an indication of the presence of unanimously declare that among the binary systems interaction and the magnitude and sign of the considered here, the interactions in toluene + iso- parameters are measure of interaction 29 . The highly butanol system are found to be stronger while that of fluctuating excess molar volume assures the existence aniline + toluene is weaker. This confirms the of interaction in the mixtures but the –ve possibility of azeotropic formation between toluene compressibility (up to 0.7 mole fraction) in toluene + and iso-butanol. 808 INDIAN J PURE & APPL PHYS, VOL 49, DECEMBER 2011

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