Pressure Dependence of the Solubilities of Anthracene and Phenanthrene in Water at 25°C

Solubilities of anthracene and phenanthrene in water were measured at 298.15K at pressures to 200 MPa and were found to decrease with increasing pressure.From the pressure coefficients of the solubilities, the volume changesaccompanying the dissolution were estimated to be 15.1±0.6 cm³-mol–1 for anthraceneand 12.4±0.3 cm³-mol–1 for phenanthrene. The partial molar volumes of thesesolutes in water are presumed to decrease with increasing pressure, contrary to thenegative compressibility of alkylbenzenes previously observed in water. Volumechanges accompanying hydrophobic hydration are also estimated to be 1.4cm³-mol–1 for anthracene and 4.1 cm³-mol–1 for phenanthrene, respectively. Thesepositive values are opposite to the negative ones usually observed for hydrophobichydration. The hydration structure of these hydrocarbons is discussed.