Catalytic activity of humic substances in condensation reactions

Abstract Humic substances (HS) have considerable impact on the fate of organic xenobiotics in natural environments. This paper reports on the catalytic activity of HS in condensation reactions of carbonyl compounds with active methylene compounds, using Knoevenagel and Claisen-Schmidt reactions as examples. Of the HS, the aquatic fulvic acids are the most active, but the velocity of condensation reactions depends also on the temperature, concentration and form of HS (free or salt) used, and the solvent.