The distribution of pyruvic acid between water and a tertiary aliphatic amine dissolved in various diluents of proton-donating and -accepting, polar and inert types and a comparison made with the extraction equilibria of pure diluent alone (I-hexanol and trichloroethylene) has been studied at 298 K. The 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 mainly promoting the formation of the acid-amine (1: 1) structure. The influence of the acid structure over distribution has been evaluated through comparing the extractabilities of seven acids containing different functional groups, i.e., benzoic. valeric. formic, levulinic, acetic, pyruvic and nicotinic acids. The results were correlated using various versions of the mass action law, i.e., a modified Langmuir equilibrium model and a chemical model approach comprising the formation of one or two acid-amine aggregated structures. (c) 2006 Elsevier B.V. All rights reserved.