Infrared study of water-benzene mixtures at high temperatures and pressures in the two- and one-phase regions

Infrared spectra of water-benzene mixtures have been observed at temperatur es and pressures in the 473-648 K and 100-350 bar ranges. The OH stretching band intensities of HDO in the benzene-rich phase in the two-phase region and in the one-phase region were obtained as a function of temperature and pressure. The band intensity, as a measure of water concentration, increase s by about three times as the temperature rises from 473 to 523 K, while it is almost independent of pressure in the 100-350 bar range at these temper atures. At higher temperatures, on the contrary, the absorption intensities exhibit remarkable pressure dependence. They increase by an order of magni tude as the pressure increases from 100 to 350 bar. These temperature-press ure dependent changes of water concentration can be properly understood wit h a phase diagram of the water-benzene mixture. The absolute concentration of water in the benzene-rich phase and in the homogeneous one phase has bee n estimated from the absorption intensities by using a simple empirical rel ationship. The resulting values are consistent with literature data, which were obtained by composition analyses of the mixtures. The effect of temper ature and pressure on the water solubility in the benzene-rich phase has be en argued in terms of energies of solvation and cavity creation for a solut e molecule. Coalescence of the hydrogen-bonded and hydrogen-bond-free OH st retching bands has been observed at higher temperatures and discussed in te rms of rotational motion of water molecules in a hydrogen-bonded cluster. ( C) 2000 American Institute of Physics. [S0021-9606(00)50929-5].