Distribution of formic and levulinic acids between water and Alamine 308 (triisooctylamine) dissolved in C-6-ring included diluents of proton-donating and accepting (cyclohexanone, methylcydohexanol), polar (1,2-dichlorobenzene, 1,2-DCB) and inert (toluene) types, as well as a comparison with the extraction equilibria of pure diluent alone (1-hexanol) have been studied at 298 K. From tested C-6 ring-containing diluents, cyclic alcohol/amine system yields the highest synergistic extraction efficiency. The strength of the complex solvation was found to be reasonably large for halogenated aromatics favouring mainly the formation of acid,-amine, structure. The influence of the acid structure over distribution has been evaluated through comparing the extractabilities of four acids containing different functional groups, i.e. formic, levulinic, nicotinic and valeric acids. The results were correlated using a modified linear solvation energy relation (METLER) and versions of the mass action law. i.e. a chemodel approach and a modified Langmuir equilibrium model comprising the formation of one or two acid-amine complex formation. (C) 2000 Elsevier Science B.V. All rights reserved.