In this work, a molecular design of solvents program based on A-UNIFAC, a revised UNIFAC model where specific association interactions are taken into account, is applied to the removal of organic chemicals found in wood hydrolysates that are toxic for the fermentation of saccharified aqueous solutions to produce ethanol. The fundamentals of computer aided molecular design are discussed as well as the characterization and feasibility rules for the synthesis of feasible molecules. The detoxification process is analyzed from the point of view of solvent selection for liquid extraction and the primary solvent properties; the solvent-environmental properties and other solvent constraints to be applied in the computer aided molecular design are presented.