Infrared study of water in benzene at high temperatures and pressure

Infrared spectra of isotopic mixtures of water dissolved in benzene at temperatures in the 373-533 K range and at constant pressure of 100 bar have been measured. The absorption intensities of the OD and OH stretching bands of HDO increases greatly with increasing temperature, indicating increase in solubility of water in benzene. Furthermore, the band shapes exhibit remarkable temperature dependence. This is due to increase in hydrogen bonded species relative to a monomeric species with increasing temperature. Concentrations of HDO in benzene have been estimated from the observed intensities by use of empirical relationships between molar absorption intensities and band peak wave numbers for hydrogen-bonded HDO. The result indicates that the solubility of water in benzene at 533 K and 100 bar is about 40 times larger than that at 293 K and I bar. The major part of the hydrogen-bonded species are attributed to dimeric species from comparison of the peak wave numbers of component bands with those reported for water in the gas phase and in low temperature matrices. Assuming a monomer-dimer equilibrium, it is shown that the rate of increase in solubility of water with increasing temperature is larger than the rate of decrease in the equilibrium constant due to an entropy effect. (C) 1998 American Institute of Physics. [S0021-9606(98)52004-1].