EXCESS MOLAR HEAT-CAPACITIES AND EXCESS MOLAR VOLUMES OF BINARY-MIXTURES OF 1,1,2-TRICHLOROTRIFLUOROETHANE (FREON 113) WITH OXYGENATED AND HYDROCARBON SOLVENTS

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), +cyclohexane (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(p)E 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(p)E curves for F113+DPE, +DIPE and +MTBE finds its origin in the physical contributions to C(p)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).