Non-Polar Solvents [Xz+ ~

Indian Journal of Chemistry Vol. 20A, March 1981, pp. 221-224 I r ~ Viscometric Study of Molecular Interactions In Binary Liquid Mixtures of Polar &: Non-polar Solvents

R. R. YADAVA* & s. s. YADAVA Chemistry Department, Gorakhpur University, Gorakhpur 273 001

Received 7 May 1979; revised 15 July 1980; re-revised and accepted 6 August 1980

Viscosities of polar solutes, acetone and methyl ethyl ketone in admixture with non-polar solvents like cyclohexane, benzene, p-xylene and mesitylene have been measured at 34.2°C. The viscosities of binary mixtures prepared with cyclohexane show appreciable negative deviation from rectilinear dependence on mol. fraction. However, this deviation is gradually reduced in the case of benzene, p-xylene and mesitylene. The parameter (d) has been calculated for each mixture and the values show a trend similar to that shown by viscosities. An attempt has been made to corre- late the deviation of viscosity from the rectilinear dependence and the d values with strength of the interaction. It is pointed out that it is more logical to associate the value of the parameter (d) with the degree of the interaction rather than its type. Viscosity data have also been used to obtain a value for the interchange energy (WylBc). Corre-

lation between WvlBC, anticipated heat of mixing and the degree of interaction has been pointed out.

HE importance of dipole-induced dipole inter- are: 0.004050 and -0.68915 respectively. As a actions and steric factors in the formation of further check of values of a and b viscosities of T a molecular complex between a polar solute acetone and p-xylene were determined by noting their (A) and a non-polar aromatic solvent (B) has been time of flow. The agreement with the literature emphasizedv" on the basis of NMR studies. The values was good as shown below : contentions have also been supported by dielectric studies+". The molecular interactions in binary Viscosity (cp) at 34.ZOC liquid mixtures have also been studied on the basis of viscosity measurements+". This work Lita In this paper we have employed viscosity measure- 0.29112 ments for the study of molecular interaction in binary Acetone 0.290 liquid mixtures consisting of polar solutes like acetone p-Xy1ene 0.539 0.53813 and methyl ethyl ketone and non-polar solvents with (a) Interpolated values progressive change in polarisability and ste~ic en- vironment, e.g. benzene, p-xylene and mesitylene. Kinematic viscosities (\I) were converted into dyna- Studies have also been made using cyclohexane as mic viscosities ("YJ)by multiplying the former with p. inert solvent with a view to providing a reference Viscosity data reported here are correct to point for the assessment of interactions. ± 0.001 cp. Materials and Methods Values of the parameter (d) were calculated by Eq. (2), The solutes and the solvents employed were of spectroscopic grade (BDH or E. Merck). Viscosities .. (2) of the binary mixtures were determined with a modi- fied Ubbelchde kinematic viscometer-P. Density of first suggested by Grunberg and Nissan-». In Eq. (2) the mixture was measured pyknometrically. Pre- "YJ1and "t)2are the viscosities and Xl and X2 the cautions were taken to avoid losses by evaporation. mol fractions of the component 1 and 2 respectively. Kinematic viscosity, v was obtained from the two '1')1is2 the viscosity of the solution. The constant term equation+ . d is proportional to w, w being the interchange energy. Viscosity data were evaluated to obtain a 'I') b v = -=at-- ... (1) value for the interchange energy (WV!sc)employing p t Eq. (3)

where 'I') and p are the viscosity (dynamic) and 2.30258R T log ("YJ12/"t)!) density respectively of the liquid and t is the time of WvlSC •. (3) flow in seconds, a and b are characteristic constants A1X1X2 Xl] of the viscometer which were determined by measur- [Xz + ~: ing the time of flow for two liquids of known viscosity. Values of the constants a and b at 34.ZOC where the term carry their usual meaning-s.

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Results and Discussion solvent mixture of a certain composition becomes Viscosity data for the binary mixtures studied at less fluid i.e. more viscous, in view of enhanced ~4.ZOC as a function of the composition are reported intermolec~lar forces between unlike pair of mole- in Table 1 and 2. There is an appreciable negative ?ules. Thl~ enha~cement could be due to dipole- deviation from rectilinear dependence of viscosity induced dipole interaction proportional to the on mol fraction for the mixture containing the polar polariza~ility of the aromatic molecule. As p-xylene solute and cyclohexane (Figs 1-4). This negative and mesitylene are more polarisable than benzene ~eviation is sufficiently reduced when cyclohexarre increased interaction of the polar solute with th~ fhydrocarbon. Steric crowding forces between pairs of like molecules and that is why the mixture is more fluid, i.e. less viscous. This is quite likely in view of the known tendency of ace- TABLB2 - VISCOSITIESd, -VALUES AND INTERCHANGBENERGY tone to associate. However, polar solute-aromatic (WTI.e) OF BINARYMIXTURESOF MBTHYLETHYLKETONEWITH NON-POLARSOLVENTAND WITH CYCLOHEXANE [Values at 34.2°C] TABLE 1- VISCOSITIES,d-VALUES AND INTERCHANGEENERGY

(Wvl ee) OF BINARY MIXTURESOF ACETONEWITH NON-POLAR Mol fro of EMK (cp) d WTI•• SOLVENTANDWITH CYCLOHEXANE (cal mol <) METHYLETHYLKETONE(EMK)-CYCLOHEXANB [Values at 34.2°C] 0.0000 0.760 (cp) Mol fro of d Wvl •• 0.1093 0.648 -0.77 1914 acetone (cal rnol=) 0.3610 0.504 -0.57 1230 0.4975 0.453 -0.53 1067 ACETONE-C¥CLOHEXANE 0.5550 0.429 -0.57 1129 0.6809 0.413 -0.38 701 0.000 0.760 0.8865 0.366 -0.43 734 0.0910 0.662 -0.62 1417 1.0000 0.350 r 0.3116 0.512 -0.44 913 <. 0.3949 0.461 -0.50 1000 0.4589 0.431 -0.50 984 METHYLETHYLKETONE-BENZENE 0.5299 0.402 -0.51 966 0.7897 0.323 -0.57 995 0.0000 0.530 1.0000 0.290 0.0925 0.501 -0.21 551 0.2405 0.462 -0.21 508 ACETONE-BENZENE 0.3178 0.446 -0.19 449 0.4477 0.424 -0.15 347 0.0000 0.530 0.5084 0.410 -0.18 413 0.1115 0.492 -0.07 167 0.6160 0.394 -0.17 378 0.3573 0.419 -0.09 187 0.7356 0.378 -0.17 355 0.4938 0.382 -0.12 254 1.0000 0.350 0.5562 0.374 -0.05 113 0.6464 0.352 -0.09 1"l7 0.8853 0.308 -0.09 176 METHYLETHYLKETONE-p-XYLENE 1.0000 0.290 0.0000 0.539 ACETONE-p-XYLENE 0.1273 0.515 0.09 -227 0.3110 0480 0.09 -231 0.0000 0.539 0.3949 0.457 0.D2 - 62 0.1403 0.500 0.10 -236 0.5326 0.434 0.05 -145 0.4308 0.429 0.16 -397 0.5913 0.419 0.01 - 39 0.5768 0.400 0.24 -626 0.6949 0.401 0.02 - 55 0.6298 0.385 0.23 -601 0.7871 0.388 0.07 -183 0.7285 0.353 0.14 -378 1.0000 0.350 0.9118 0.311 0.19 -517 1.0000 0.290 METHYLETHYLKETONE-MESITYLENE

ACETONE-MESITYLENE 0.0000 0.584 0.1256 0.549 0.D2 - 62 0.0000 0.584 0.3266 0.500 0.05 -154 0.1387 0.541 0.17 --422 0.4175 0.479 0.06 -186 0.4493 0.447 0.19 -517 0.5581 0.443 004 -115 0.5975 0.403 0.20 -563 0.6213 0.428 0.03 - 95 0.6567 0.383 0.17 --491 0.7133 0.409 0.04 -137 0.7521 0.362 0.26 -785 0.8019 0.389 0.03 - 85 0.9168 0.313 0.24 -767 0.9035 0.368 0.01 - 28 1.0000 0.290 1.0000 0.350

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0.8 0·8

0'2 0·2

0·4 0·10 o.a /·0 0·2 0'4 0'10 0·8 /0

MOl Fr. OF ACETONE Mol Fr.OF ACETONE Fig. 1 - Viscosity at 34.2°C versus mole fraction of acetone Fig. 3 - Viscosity at 34.2°C of acetone-mesitylene mixture [Acetone-cyc1ohexane mixture, 0; acetone-benzene mixture, b) versus mole fraction of acetone

0.8

0·10

0.2

0'2

0.2 0.4 0·10 0·8 /.0

0·4 0·10 0·8 /·0 Mol Fr. OF ETHYL METHYL KETONE

Mol Fr. OF ACETONE Fig. 4 - Viscosity at 34.2°C versus mole fraction of methyl ethyl ketone [methyl ethyl ketone-cyclohexane mixture, @ ; Fig. 2 - Viscosity at 34.2°C of acetone-s-xylene mixture methyl ethyl ketone-benzene mixture, b) versus mole fraction of acetone large and positive d-value indicated strong specific on the aromatic hydrocarbon, due to methyl substi- interaction; small positive values indicated weak tition would make the flow process still more difficult specificinteraction, and large negative value indicated i.e. will enhance the viscosity which is in line with no specific interaction. the experimental observations reported here. It is evident from Tables 1 and 2 that d-values are However, a comparison of the viscosity data for large negative with cyclohexane, small negative with the polar solutes acetone and methyl ethyl ketone benzene and small positive with p-xylene and mesi- with p-xylene and rnesitylene shows that the mix- tylene for both the solutes. The three aromatic sol- tures with mesitylene show slightly greater negative vents are expected to have similar interactions with deviation as compared to those prepared with p- the polar solutes. In viewof the above, it seemsmore xylene. This behaviour becomes more pronounced appropriate to regard the parameter (d) as a measure in the case of binary mixture with methyl ethyl ketone of the resultant interaction rather than to associate than those with acetone. This indicates that a higher different range of d-values with different type of steric overcrowding on the interacting molecules exclusive interactions. Large negative d-values for has a tendency to adversely affect the intermolecular binary mixtures with cyclohexane indicate the forces between pairs of unlike molecules due to existence of weak interaction due mainly to disper- blocking effect-. sion forces. Increased (less negative) d-values for In an earlier publication- d-values were said to mixtures of polar solutes with benzene indicate indicate various types of interactions as follows : stronger interaction due to appreciable dipole induced 223 INDIAN J. CHEM., VOL. 20A, MARCH 1981

0'8 0·8

0·5 0·2

0·2 0'4 0·6 o-a 1·0 0·2 0·4 o·a 1·0

MOl Fr. OF ETHYL METHYL KETONE Mol Fr. OF ETHYl METHYL KETONE Fig. 5 - Viscosity at 34.2°C of methyl ethyl ketone-s-xylene Fig. 6 - Viscosity at 34.2°C of Methyl ethyl ketone-mesitylene mixture versus mole fraction of methyl ethyl ketone mixture versus mole fraction of methyl ethyl ketone dipole interaction. Still higher (positive) d-values Acknowledgement for the mixtures prepared with p-xylene and mesi- The authors are thankful to Prof. R. P. Rastogi tylene seem to be due to enhanced dipole-induced for his interest in the work and to the UGC, New dipole interactions on account .of higher polarisa- Delhi for financial assistance. bility of the methyl substituted benzenes. However, d-values for p-xylene and mesitylene mixtures pre- References pared with methyl ethyl ketone as compared to 1. HOMER,J. & YA,DAVAR. . R .• J. chem. Soc., Faraday Trans. those with acetone once again indicate the reduced 1.. (1974). 611. dipole-induced dipole interactions due to steric over- 2. HOMER.J. & YA,DAVAR.. R .. Tetrahedron. 29 (1973).3853. corwding-, Variation in d-value with the composition 3. YADAVA.R. R. & YA,DAVA.S. S., Indian J. Chem., 16A of the mixture in any series is not large and can not (1978). 826. 4. YADAVA.R. R. & YA,DAVA.S. S.• Indian J. Chem., 18A be correlated to draw any conclusion. (1979), 120. A perusal of WvlsC values given in Tables I and 2 5. FORT. R. J. & MOORE. W. R., Trans. Faraday Soc .• 62 shows that for both the solutes Wvlsc is highly (1966), 1112. 6. RAMAN. G. K .• NAIDU. P. R. & KRISHNAN.V. R .• Aust, positive with cyclohexane, less positive with benzene J. Chem., 21 (1968). 2717. and slightly negative with p-xylene and mesitylene 7. NIGAM. R. K. & SINGH. P. R .• Indian J. Chem .• 9 (1971). again showing a graded behaviour. 691. 8. NIGAM. R. K. & MAHL. B. S.• Indian J. Chem.,9 (1971). Values of interchange energy (Wvlsc) as obtained 1255. by viscosity measurements seem to fall in line with 9. GOPAL, R .• AGRAWAL.S. & AGRAWAL.D. K .• J. Indian the values of heat of mixing anticipated on the basis chem. Soc .• 55 (1978), 501. of the degree of interaction in various mixtures. 10. UBBELHODEL. ., Ind. Engng. Chem. (Anal. Edn.). 9 (1937). 85. Small negative values of Wvlsc for polar solute 11. WEISSBERGER.A., Technique of organic chemistry. Vol. 1 p-xylene (or mesitylene) mixtures, indicating evolu- (Interscience, New York). 1959. tion of heat, clearly shows that the attractive forces 12. WEAST. R. C .• Hand book of chemistry and physics (The between the pairs of unlike molecules in such mix- Chemical Rubber Co .• Ohio). 1971. 13. TIMMERMANS.J.• Physico-chemical constants of pure organic tures have overtaken the interaction between pairs compounds (Elsevier. New York). 1950. of like molecules. 14. GRUNBERG.L., Trans. Faraday Soc .• 50 (1954). 1293.

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