Excess molar heat capacities and excess molar volumes of binary mixtures of 1,1,2-trichlorotrifluoroethane (Freon 113) with oxygenated and hydrocarbon solvents

Abstract

Excess molar heat capacities C p E were determined at 298.15 K for the following thirteen mixtures with 1,1,2-trichlorotrifluoroethane (F113): +acetone (ACT), +dipropyl ether (DPE), +diisopropyl ether (DIPE), +methyl t-butyl ether (MTBE), +tetrahydrofuran (THF), +1,4-dioxane (DIOX), +methyl acetate (MAC), +benzene (BENZ), +cyclo-hexane (cC6), + n-hexane (nC6), +2,2-dimethylbutane (22DMB), + n-heptane (nC7) and +2,4-dimethylpentane (24DMP). Excess molar volumes V E at 298.15 K were also measured for the following mixtures: F113 +DPE, +MTBE, +DIOX, +BENZ, +cC6, +22DMB, +nC7 and +24DMP. V E data for the remaining five mixtures (those with ACT, DIPE, THF, MAC and nC6) were previously reported. The C E p for all oxygenated solvents is positive, whereas for the equal-structure hydrocarbon solvents (taken as homomorphs) it is almost zero or negative. This is interpreted in terms of the formation of an F113-oxygenated compound complex in the solution. Further support for the existence of this complex is given by V E, which for the oxygenated solvents is always smaller than for the hydrocarbon compounds. The use of the homomorphs indicated that (i) the asymmetry of the C 9 E curves for F113 +DPE, +DIPE and +MTBE finds its origin in the physical contributions to C 9 E rather than in the presence of the complex, and (ii) the most probable stoichiometry of the complexes is 1:1 for MTBE, DPE and DIPE, while for DIOX the 2:1 complex is also present. The F113-oxygenated solvent complex is probably formed through a charge transfer mechanism and it is energetically weak (enthalpy of formation 2–3 kJ mol −1).