The autoprotonation in reduction mechanism of pesticide ioxynil

The reduction mechanism of ioxynil (3,5-diiodo-4-hydroxy-benzonitrile) was studied in dimethylsulfoxide using the electrochemical methods (tast polarography, cyclic voltammetry and controlled potential electrolysis) combined with GC/MS identification of products. The reduction is accompanied by the cleavage of iodide yielding 3-iodo-4-hydroxybenzonitrile. Surprisingly, this process requires only one electron for the exhaustive electrolysis of the starting compound. We showed that the apparent one electron reduction observed in the aprotic solvent is due to the autoprotonation by another molecule of ioxynil. The overall one electron reduction (uptake of two electrons per two molecules of ioxynil) is changed in the presence of a strong proton donor to a two electron process per one molecule.