Partitioning of aromatic molecules in aqueous biphasic systems

Aqueous biphasic systems (ABS) may be suitable for the separation of aromatic molecules in industrial and environmental settings; hence it is invaluable to have predictive models of partitioning behavior in these systems for design and evaluation purposes. In a continuing study of the partition of small aromatic organic molecules, the distribution of several relatively hydrophilic substituted benzene species is reported. The partitioning behavior of five charged substituted benzene species (phthalic acid, 4-hydroxybenzoic acid, benzoic acid, salicylic acid, and p-toluic acid) and one uncharged species (1,3-dinitrobenzene) has been studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts [K3PO4, K2CO3, (NH4)(2)SO4, and NaOH]. Comparison has been made with published data on the partitioning of these solutes in 1-octanol/water biphasic systems. In general, the partition of these species may be understood in terms of the free energy of hydration of the salt forming the ABS and the dissociation of the charged groups of the distributed solutes.