Volume Change for Hydrophobic Hydration of Biphenyl

The solubility of biphenyl in water at 298.2 K was measured at pressures up to 200 MPa. The logarithm of the solubility linearly decreased with increasing pressure. From the value of the slope, the volume change for the dissolution of biphenyl in water was thermodynamically estimated to be 11.8±0.5 cm³⋅mol⁻¹. The solution density of biphenyl in carbon tetrachloride at 298.2 K and 0.10 MPa was also measured to estimate the partial molar volume of the solute. Using these values and the molar volume of solid biphenyl, the volume change for the hydrophobic hydration of the biphenyl was estimated to be −6.5±1.6 cm³⋅mol⁻¹. The value was compared with those of methylene group and other aromatic hydrocarbons as a function of the rotational molecular diameter of these hydrophobic solutes.