EXCESS MOLAR ENTHALPIES OF BINARY-MIXTURES OF 2-BROMO-2-CHLORO-1,1,1-TRIFLUOROETHANE (HALOTHANE) WITH OXYGENATED AND HYDROCARBON SOLVENTS

Excess molar enthalpies, H(E), were determined at 298.15 K for the following eighteen mixtures: 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane)+acetone, +dipropyl ether, +diisopropyl ether, +methyl tert-butyl ether, +ethylene glycol dimethyl ether or monoglyme, +diethylene glycol dimethyl ether or diglyme, +tetraethylene glycol dimethyl ether or tetraglyme, +methyl phenyl ether, +tetrahydrofuran, +1,4-dioxane, +methyl acetate, +benzene, +cyclopentane, +cyclohexane, +n-hexane, +n-heptane, +2,2-dimethylbutane and +2,4-dimethylpentane. The value of H(E) for all oxygenated solvents is strongly negative whereas for the equal-structure hydrocarbon solvents (taken as homomorphs) it is positive. This is a clear indication of the formation of a halothane-oxygenated-compound complex. The complexation is through a H-bond between the oxygen atom in the solvent molecules and the hydrogen atom in halothane. As the number of oxygen atoms in the solvent increases, H(E) becomes more negative and asymmetrical, its minimum being displaced towards higher halothane concentrations. The H(E) values for halothane mixed with the glymes are amongst the largest ever found for mixtures of non-electrolytes. The increase in asymmetry in going from monoglyme to tetraglyme is indicative of the presence of multisolvated species in the solution. A clear correlation between the solvent Kamlet-Taft beta parameter (H-bonding acceptor ability) and H(E) was found. A comparison between the H(E) vs. beta correlation for the present data and that for chloroform showed that for a given oxygenated solvent H(E) with halothane is always more negative than with chloroform. This indicates that the acidity of the hydrogen atom in halothane is greater than that in chloroform.