Distribution of picolinic acid between water and Alamine 336, a mixture of tertiary aliphatic amines, dissolved in various diluents of proton-donating and -accepting, polar and inert types, as well as a comparison with the extraction equilibria of pure diluent alone (l-octanol and 1,2-dichlorobenzene) have been studied at 298 K and the phase ratio of 1: 1 (v/v). Cyclic alcohol/amine system yields the largest synergistic extraction efficiency. The strength of the complex solvation has been found to be reasonably high for halogenated aliphatic hydrocarbons promoting mainly the formation of acid(1)-amine(1) structure. The influence of the acid structure over distribution has been evaluated through comparison of the extractabilities of five acids containing different functional groups, i.e., formic, levulinic, acetic, valeric, and picolinic acids. The results were correlated using various versions of the mass action law, i.e., a modified Langmuir equilibrium model and a chemical modeling approach comprising the formation of one or two acid-amine aggregated structures. (C) 2004 Elsevier B.V. All rights reserved.