Rastogi, R. P.

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CommunicationsMolecular Interactions in Binary Mixtures ofChloroform with Benzene & Toluene*R. P. RASTOGIChemistry Department, Gorakhpur University, GorakhpurandR. R. MISRAHindu College, University of Delhi, Delhi 110007Received 8 April 1976; accepted 1 May 1976Chemical contribution to excess enthalpy for thebinary mixture of chloroform with benzene and toluenehave been calculated assurning 1 : 1 complex formation.The difference in the calorimetric and calculated excessenthalpy is attributed to physical (non-complextng)contribution.WE reported- excess enthalpies of binary mixturesof chloroform with aromatic hydrocarbons andconcluded qualitatively that hydrogen bonding werethe predominant interactions in these mixtureswithout any mention of the physical (non-com-plexing) contribution. However, the observedexcess enthalpy may conveniently be divided intophysical (non-complexing) and chemical contribu-tions, the latter being due to complex formations.Chemical contribution to excess enthalpy can becalculated from equilibrium constant data obtianedfrom spectral studies. The difference between thecalorimetric excess enthalpy and spectroscopicallycalculated excess enthalpy should be related to thephysical contribution. In this note we have estimat-ed the physical and chemical contributions to excessenthalpies for the binary mixtures of chloroform withbenzene and toluene.There is good evidence for association of chloroform(A) with aromatic hydrocarbons (B) to form 1: 1complex in the solid state" and in the liquid statt3-5,via hydrogen bonding. The association of chloroformwith aromatics is represented by.. , (1)The equilibrium constant of the association re-presented by Eq. (1) would be given by Eq. (2),K=r(l-r)/(xAxB-r+r2) ••• (2)where r represents the ratio of the amount of thecomplex AB formed at equilibrium to ~he sum. ofthe stoichiometric amounts of A and B 1Jl the mix-ture; XA and XB are the stoichiometric mole fractionsof A and B respectively.The chemical contribution of excess enthalpy H~ ofcomplex formation due to hydrogen bond inter-*Forms a part of the Ph.D. thesis.action can be calculated from the relation (3),H~ = r(~H) ... (3)\\:he.re ~H is t~e e?thalpy of hydrogen bond asso-ciation. SubstJtntlJlg the value of r from Eq. (2) inEq, (3), we obtain an expression for H~ as a functionof mole fr2.ctions of the two components Aand B.However, the calorimetric excess enthalpy HEmay ?e taken as the Sum of physical and chemicalcontributions,HE = HE+HE (4)pc ...where H~ and H~ represent the physical and chemicalcontributions respectively.In Fig. (1) are compared the calorimetric- excessenthalpies with the chemical contributions arisingfrom the formation of the CHCI3.CsHs and CHCI3.C6H5CH3 complexes. The equilibrium constant and~H values for both the systems are those reported1Jl references (5) and (6) respectively.The chemical contribution to excess enthalpy isgreater than the calorimetric excess enthalpies forboth of the binary mixtures. This clearly indicatesthat the physical contribution to excess enthalpyshould be positive, which is obvious because theexcess enthalpy for a mixture of carbon tetra-+300r--------------------[-b-I------------~+200, .... ----- .._-- ...".,<1"'"".----;~::=,'- -- -------- [_QI-- ,. --" ... -;""; ---------200i0E -4~-wx:-600iiiiiiiiii/.'I;"/.II;/I./[bl ,,/..•..•..._.,..-800-1000~--..,._!,_----:t_:_--__:__:__---:!-::----~o ·2 0'4- 0·8 0-8Mole fro of chlOroformFig. 1 - Comparison of excess enthalpies for (a) chloroform+benzene and (b) cbloroform-j-toluene [(-) calorimetericdata (ref. 1); (-.-) spectroscopic data (Eq. 3); and (----)physical contribution (Eq. 4)]521INDIAN J. CHEM., VOL. 14A, JULY 1976chloride-l-cyclchexane is positive? where a purephysical interaction would be expected.The complex bonding between chloroform andaromatic hydrocarbons similar to other hydrogenbonds, is essentially electrostatic in character, but isconsiderably less stable than the more commonhydrogen bond due to weak ionic character of theC-H bond. This is consistent with the lower valueof chemical contribution to excess enthalpies ofchloroform with benzene and toluene, which are-0·5 and -0·9 kJ mole'< respectively for equimolarmixtures.522Reference1. RASTOGI, R. P., NATH, J. & MISRA, R. R., J. chem:Thermodynamics, 3 (1971). 307.2. MCGLASHAN, M. L., An. Rep. Chem. Soc., LIX (1962), 73.3. REEVES, L. VV. & SCHNEIDER, \V. G., Can. J. Chem., 35·(1957), 25t.4. PERRI-NS, N. C. & SIMONS, J. P., Trans. Faraday Soc .•65 (1969), 390.5. WEI-CHUWAN, LIN & SHYR-JIN, TSAY, J. pliys. Chem.,74 (1970), 1037.6. JOHNSTON (Jr), M. D., GASPARRO, F. P. & KUNTZ (Jr),1. D., J. Am. chem. Soc., 91 (1969), 5715.7. ADCOCK, D. S. & MCGLASHAN, M. L., Proc. r . Soc., London.A226 (1954), 266.

Molecular Interactions in Binary Mixtures of Chloroform with Benzene & Toluene*

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Molecular Interactions in Binary Mixtures of Chloroform with Benzene & Toluene*

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