Hydration to Benzo-15-crown-5, Benzo-18-crown-6 and the Benzo-18-crown-6-Potassium Ion Complex in the Low-Polar Organic Solvents

The coextraction of water with benzo-15-crown-5 (B15C5), benzo-18-crown-6 (B18C6) and the B18C6-K^+ complex into seven low-polar solvents, i.e., carbon tetrachloride (CTC), chloroform (CF), dichloromethane (DCM), 1,2-dichloroethane (1,2-DCE), benzene (BZ), chlorobenzene (CB) and o-dichlorobenzene (o-DCB), has been investigated. The mean hydration number, n_<H2O>, of these solutes in the water-saturated organic solvents was determined. There is a trend that the n_<H2O> values for any solutes increase with increasing the water concentration in the solvents. Those of B18C6 and B15C5 converge at almost 0.8 for B18C6 and 0.4 - 0.5 for B15C5 in the solvents with the relatively high water concentration, i.e., CF, 1,2-DCE, DCM, and nitorobenzene (NB). The n_<H2O> value of B15C5 is about one-half of that of B18C6 for a given organic solvent. The dominant species of the B18C6-K^+ complex in these solvents is non-hydrated. From these results, the hydration equilibrium constants, K_<H2O>,o, in the organic solvents were estimated