Thermodynamic properties of some binary liquid mixtures.

The excess enthalpies and volumes of mixing have been measured for a number of cyclic ethers with benzene and cyclohexano. In addition the enthalpies of milling of hexafluorobenzene + 1,4-dioxan have been measured. The studies suggest that a rather weak specific interaction occurs between benzene and some cyclic ethers. The present results show reasonable correlation with other estimates of the electron-donor ability of the ethers; the interaction between benzene and the oxygen lone pair may involve a charge-transfer mechanism. Replacing benzene with a stronger acceptor, hexafluorobenzene, enhances the interaction. Volumes of mixing of 1,4-dioxan with several hydrocarbons have also been measured. An apparatus is described for the precise measurement of vapour pressures; preliminary measurements have been made to test the operation of the apparatus. Work on fluorocarbon + hydrocarbon mixtures is described in the Appendix. The results indicate that it is the shape of the hydrocarbon that is the dominant factor governing the magnitude of the excess function and that TT-TT interactions play a secondary role in this respect.