A frequent problem in the production of organic compounds via partial oxidation are unwanted byproducts, like acetic acid. Here, the convenient method for working-up the aqueous acidic effluents (containing up to 10 wt.-% acid) after removing the main product is the extraction. The influence of various extractant systems containing organic solvents and trialkylamines on distribution coefficients and selectivities of acids has been studied. Acetic acid and lactic: acid served as model compounds for acidic byproducts and acidic fermentation products, respectively. Experimental results indicate that combinations of tri-n-hexylamine and an alcohol show greatest synergistic effects and as a consequence comparably high distribution coefficients.