Thermodynamic behaviour of some aromatic fluorocarbon solutions.

An apparatus has been developed to measure the vapour pressures of mixtures by a static technique. The apparatus has been tested by reproducing the vapour pressures and excess Gibbs functions for mixtures of hexafluorobenzene + cyclohexane. Excess Gibbs functions have been determined for hexafluorobenzene +N,N-dimethlaniline, and isopropylcyclohexane. An equilibrium constant for complex formation Kx, has been calculated from these quantities and compares favourably with the spectroscopically determined Kx. Excess Gibbs functions have also been determined for mixtures of pentafluorocyanobenzene + cyclohexane at two temperatures. The solid-liquid phase diagram has been determined for hexafluoro-benzene +N,N-dimethyl p-toluidine and shows the existence of a 1:1 complex in the solid. The liquid-liquid phase diagram for pentafluorocyanobenzene + isopropylcyclohexane has also been determined, and the system shows an upper critical solution temperature. Excess volumes of mixing have been obtained for hexafluorobenzene +N,N-dimethylaniline, N,N-dimethyl p-toluidine and isopropylcyclohexane and pentafluorocyanobenzene +N,N-dimethylaniline, N,N-dimethyl p-toluidine, benzene, toluene and p-xylene. Excess enthalpies of mixing have been measured at two temperatures for pentafluorocyanobenzene + cyclohexane, benzene, toluene and p-xylene. The experimental evidence suggests that strong complexing occurs in solution between aromatic fluorocarbons + aromatic hydrocarbons, and also aromatic amines. In the former case the interaction appears to be mainly of an electrostatic nature, whereas in the latter case the major contribution to the interaction arises from charge transfer forces, the amine acting as an electron donor.