Reductive dechlorination of a chloroacetanilide herbicide in water by a Co complex-supported catalyst

Abstract Chloroacetanilide herbicides are widely used pesticides in agriculture, resulting in contamination of ground and surface waters. Among the methods studied to enhance their degradation rate, reductive dechlorination is proposed. A [Co(bpy(CH 2 OH) 2 ) 2 ] 2+ complex allowing electrocatalytic reduction of chloroacetanilide herbicides is covalently immobilized on a 3D porous electrode previously functionalized by electrografting methods. Bulk electrolyses performed on alachlor in a flow electrochemical cell show the high catalytic activity of the Co complex, leading to a total reduction of the substrate and a good selectivity toward the formation of the dechlorinated derivative. Interestingly, when it is immobilized, the catalyst is more stable than in solution as shown by the turnover number of more than 360 compared with a value of 4 in solution. Biodegradability on 5 days did not show any improvement compared with the starting material, highlighting that even if chlorine atoms that are often responsible for the toxicity of a molecule are removed, the substrate can still have a biorecalcitrant behaviour. The main by-product, deschloroalachlor, was identified and was found to be not biodegradable accounting for this recalcitrance.