HYDROGEN-BONDING .34. THE FACTORS THAT INFLUENCE THE SOLUBILITY OF GASES AND VAPORS IN WATER AT 298-K, AND A NEW METHOD FOR ITS DETERMINATION

The solubility of 408 gaseous compounds in water at 298 K has been correlated through eqn. (i), where the solubility is expressed as the Ostwald solubility coefficient, L(w), and the solute explanatory variables are R2 an excess molar refraction, pi2H the dipolarity/polarizability, SIGMAalpha2H and SIGMAbeta2H the effective hydrogen-bond acidity and basicity, and V(x) the McGowan characteristic volume. A similar equation using the log L16 parameter instead of V(x) can also be used; L16 is the Ostwald solubility coefficient on hexadecane at 298 K. log L(w) = -0.994 + 0.577R2 + 2.549 pi2H + 3.813SIGMAalpha2H + 4.841SIGMAbeta2H - 0.869 V(x) (i) n = 408 rho = 0.9976 sd = 0.151 F = 16810 The main factors leading to increased solubility are solute pi2H, SIGMAalpha2H and SIGMAbeta2H values; conversely, the corresponding properties of water are dipolarity/polarizability, hydrogen-bond basicity and hydrogen-bond acidity. Solute size plays a minor role, and slightly decreases solubility, contrary to observations on all non-aqueous solvents. It is shown that this peculiar behaviour of water is due to (a) a greater increase in the unfavourable cavity effect with increase in solute size, for solvent water, and (b) a smaller increase in the favourable general dispersion interaction with size, for solvent water. A new method for the determination of log L(w) values is put forward, using the relationship L(w) = L16/P where L16 is as above, and P is either the water-hexadecane partition coefficient or the water-alkane partition coefficient. For 14 solutes using the former P-value, agreement with values calculated through eqn. (i) is 0.08 log units on average and for 45 solutes using the latter P-value, the corresponding agreement is 0.15 log units, with log L(w) values ranging up to 8 log units.