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 cor related through eqn. (i), where the solubility is expressed as the Ost wald solubility coefficient, L(w), and the solute explanatory variable s are R2 an excess molar refraction, pi2H the dipolarity/polarizabilit y, SIGMAalpha2H and SIGMAbeta2H the effective hydrogen-bond acidity an d basicity, and V(x) the McGowan characteristic volume. A similar equa tion 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 + 4.841SIGMAbeta 2H - 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 w ater are dipolarity/polarizability, hydrogen-bond basicity and hydroge n-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 si ze, for solvent water, and (b) a smaller increase in the favourable ge neral dispersion interaction with size, for solvent water. A new metho d for the determination of log L(w) values is put forward, using the r elationship L(w) = L16/P where L16 is as above, and P is either the wa ter-hexadecane partition coefficient or the water-alkane partition coe fficient. For 14 solutes using the former P-value, agreement with valu es 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.