Distribution of acetic acid between water and Alamine 308 (triisooctylamine) dissolved in various diluents of proton-donating and -accepting (benzyl alcohol, chloroform, methylisobutyl ketone), polar (1,2-dichloroethane), and inert (xylene) types, as well as a comparison with the extraction equilibria of pure diluent alone (1-octanol), has been studied at 298 K. Among the tested C-6 ring-containing and aliphatic diluents, the cyclic alcohol/amine system yields the highest synergistic extraction efficiency. The strength of the complex formation was found to be reasonably large for halogenated compounds favoring mainly the formation of acid(1)-amine(1) structure. The influence of the acid structure over distribution has been interpreted through comparing the extractabilities of six acids containing different functional groups, i.e., acetic, formic, levulinic, pyruvic, nicotinic, and valeric acids. The results were correlated using a linear solvation energy relation (SERAS) 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 complexes. The reliability of the proposed models has been analyzed statistically.