Excess Enthalpies of some Binary Mixtures of 1,2-Dichloroethaneand HydrocarbonsBY B. S. MAHL* and J. R. KHURMADepartment of Chemistry-Biochemistry,Punjab Agricultural University, Ludhiana, IndiaReceived 26th April, 1976The excess enthalpies of mixtures of 1 ,Zdichloroethane with cyclohexane, benzene, toluene,0-, rn- andp-xylenes have been measured at 298.15 K. HE values for the first two systems are foundto be positive over the entire composition range whereas HE changes sign with composition in therest of the systems. Examination of the results shows that there appears to be some kind of specificinteraction between aromatic hydrocarbons and 1,2-dichloroethane.It has been established 1-9 that benzene and methylated benzenes act as weakelectron donors in the formation of intermolecular complexes with carbon tetra-chloride, chloroform and methylene chloride.In this paper we deduce the presenceof such interactions for the systems 1,2-dichloroethane +benzene, +toluene, + 0-, + m- and +p-xylenes from excess enthalpy measurements.EXPERIMENTALThe materials were purified and their purity checked as reported ear1ier.lo* l1 Excessenthalpies were measured in the previously described ~alorimeter.~ The temperature of thewater bath in which the measurements were taken was controlled to better than +O.OOl K.RESULTS AND DISCUSSIONThe excess enthalpies at different mole fractions of these systems at 298.15 Kwere fitted to the expression :where x1 and x2 are the mole fractions of the components 1 and 2 in the mixture.HE/x1x2 = ho+hl(xl-x2)+h2(x1 - x ~ ) ~ + ~ ~ ( x ~ - x ~ ) ~ (1)TABLE l.-VALUES OF THE CONSTANTS OF EQN (1) AT 298.15 Ksystem ho/J mol-1 hl/J mol-1 h l / J mol-1 h3/J mol-1 aHE/J mol-11,2-dichIoroethane+1 ,Zdichloroethane+1 ,Zdichloroethane+1,2-dichIoroethane+1 ,Zdichloroethane +1 ,Zdichloroethane+benzene 260.5 229.0 167.4 - 44.7 1.4toluene - 107.5 415.1 276.1 22.0 3.9o-xylene - 77.2 702.3 232.1 - 155.2 1.5rn-xylene 60.3 901.6 292.4 - 239.2 2.6p-xylene - 258.2 658.6 399.1 21 3.2 4.2c yclo hexane 5552.9 121.6 425.5 223.9 4.1230 EXCESS ENTHALPIES OF BINARY MIXTURESThe coefficients ho, h l , h2 and h3 for each mixture, evaluated by fitting the experi-mental values of HE/x1x2 to eqn (1) by the method of least squares, are recorded intable 1, together with the estimated standard deviation a(HE) calculated from theequationwhere the sum is taken over the set of n(observed) results and rn is the number ofcoefficients.The values of HE are reproducible to within 4.0 J mol-1 and are plottedin fig. (1)-(6).O W E ) = [ W O E b s - ~cEalc)2/(~,,s - m)l+iaoo12001200no01000r( 900800?OOw 600 ' 500LOOI -230020010002 OL 0 6 08 10XIFIG. 1 .-Enthalpies of mixing HE against molefraction x1 of 1,2-dichloroethane (1) + cyclo-hexane (2)x1FIG. 3.-Enthalpies of mixing HE againstmole fraction x1 of 1,2-dichloroethane (l)+toluene (2).x1FIG. 2.-Enthalpies of mixing H E againstmole fraction xi of 1 ,Zdichloroethane (1) +benzene (2).0 2 OL 0 6 08 1 0X1FIG. 4.-Enthalpies of mixing HE againstmole fraction x1 of 1,Zdichioroethane (I)+o-xylene (2)B.S. MAHL AND J . R. KHURMA 31The HE values of 1,2-dichloroethane +benzene and 1,2-dichIoroethane + cyclo-hexane are positive over the whole range of composition whereas for 1 ,Zdichloro-ethane + toluene, + u-, + m- and +p-xylenes, HE values change sign with composition.In the case of 1 ,2-dichloroethane + benzene, HE is a maximum at a mole fraction of1,2-dichloroethane of - 0.7. The excess heat is thus markedly asymmetrical inthese systems except for I ,Zdichloroethane + cyclohexane where it is symmetrical.Such asymmetry is common in mixtures in which specific interactions occur.126050LO3020104I 10 2 -2032 -302 -Low- 50-60-70-60-90-1 no0 2 O L 0 6 0 8 1 0x1FIG.5.-Enthalpies of mixing HE againstmole fraction xl of 1,Zdichloroethane (1)+p-xylene (2).1101009080706050t LO0M -E 3o2 20z ' 0w-50 "?.i -10I L 1 ' 1 ' 1 ' " 102 o c 06 o a 1 0X1FIG. 6.-Enthalpies of mixing H E againstmole fraction x1 of 1,2-dichloroethane (1)+m-xylene (2).HE values are smaller with benzene than with cyclohexane and are smaller stilland even change sign with toluene and the xylenes as a function of composition.The sharp decrease of HE values of 1,Zdichloroethane with benzene, as comparedwith that with cyclohexane although their sizes are approximately the same, and theexothermic mixing with toluene and xylenes at low mole fractions of 1,2-dichloro-ethane provide strong evidence for the existence of specific interactions in thesesystems.This is further supported by the positive temperature coefficient of excessvolumes of mixing l3 of these systems.It is, however, difficult to comment specifically about the nature of these inter-actions from thermodynamic evidence alone. A weak complex formation l4 betweenthe n-electrons of the various aromatic hydrocarbons under the present investigationwith 1 ,Zdichloroethane could be a probable explanation for the results obtained.W. G. Schneider, J. Phys. Chem., 1962, 66,2653.C. J. Creswell and A. L. Allred, J. Phys. Chem., 1962, 66, 1469.R. P. Rastogi, J. Nath and R. R. Misra, J. Chem. Thermodynamics, 1971, 3, 307.M. L. McGlashan, D. Stubley and H. Watts, J. Chem. Soc. (A), 1969, 673.J. R. Goates, R. J. Sullivan and J. B. Ott, J. Phys. Chem., 1959, 63, 589.R. K. Nigani and B. S. Mahl, Indian J. Chem., 1972, 10, 1167. ' R. K. Nigam and B. S. Mahl, J.C.S. Faraday I, 1972, 68, 1508.a L. W. Reeves and W. G. Schneider, Canad. J. Chem., 1957, 35, 25132 EXCESS ENTHALPIES OF BINARY MIXTURESN. C. Perrins and J. P. Simona, Trans. Firaday Soc., 1969, 65, 390.3, 363.loB. S. Mahl, R. K. Nigam, S. L. Chopra and P. P. Singh, J. Chem. Thermodynamics, 1971,l1 J. N. Vij and B. S. Mahl, Thermochim. Acta, 1975, 12, 155.l2 J. S. Rowlinson, Liquids and Liquid Mixtures (Butterworth, London, 1969).l3 M. S. Dhillon, J. Chem. Thermodynamics, 1974, 6, 1107.l4 L. A. K. Staveley, W. I. Tupman and K. R. Hart, Trans. Faraday SOC., 1955, 51, 323.(PAPER 6/802