HYDROGEN-BONDING, INTERFACIAL-TENSION AND THE AQUEOUS SOLUBILITY OF ORGANIC-COMPOUNDS

From the interfacial tension of organic compounds with water and their contactable surface areas, the aqueous solubility of such compounds c an be quantitatively predicted. Vice-versa, when the interfacial tensi on with water is known for a given organic compound, as well as its aq ueous solubility, its contactable surface area can be obtained. From a ny two of these three data, and the compound's surface tension, its fr ee energy of hydration can be calculated. However the free energy of h ydration is not simply linked to a compound's aqueous solubility. For compounds which are partly apolar and partly polar, the interfacial te nsions with water must be separately determined for each part; once th ese are expressed in kT units, they can be added together, following w hich the aqueous solubility of the complete compound can be calculated (a procedure which has been used earlier to obtain the critical micel le concentrations of nonionic(1) and anionic(2) surfactants). From a c omparison between the solubilities (and the interfacial tensions) of a lcohols and those of the corresponding hydrocarbons, it is possible to obtain the (repulsive) free energy of OH-groups interacting in water, as well as the free energy of hydration of the OH-group of alcohols. The latter is about -5.6kT, or 14kT/Mole.