Solubility of Alcohols, Phenols and Anilines in Water

An equation is deduced relating the solubility s of organic substances in water to their distribution coefficient P1 at infinite dilution between cyclohexane and water, to their association constant kM in cyclohexane and to their concentration Cαin their own phase. When the phase in equilibrium with water is crystalline, the entropy of melting ΔSmelting also intervenes as well as the difference between the melting point and the room temperature. For the alcohols it appears that both P1and kM depend on the number n of carbon atoms in the molecule. In this case the equation becomes: log s = A - 0.597 n + log f, where the constant A is respectively 2.40, 2.69 and 3.05 for the primary, secondary and tertiary alcohols, f is a correction factor which depends on Cαand on kM. For solubilities lower than 1.5 mol 1−1 the mean deviation between the computed values and the literature data is 10 % in a range of solubilities from 0.0002 to 1 mol l−1. For the phenols and the anilines P1 depends on the molar volume φ and on the pKa, whereas kM is more or less influenced by the last factor. Or the basis of previously established correlations between these quantities, the solubility of various alkyl and halogenated derivatives of phenol and of aniline are computed and compared with the experimental values. The mean deviation is 25 7 for solubilities going from 0.007 to 0.9 mol 1−1. The most important factor determining the solubility of the phenols appears to be their molar volume. The role of the pKaof the phenols and of the ortho-substituents is rather small as a consequence of the cancellation of effects of these factors on P1 and on kM. However, in the case of the anilines the effect of the pKa on their solubility remains important.