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Bulk electrolysis of diuron (3-(3,4-dichlorophenyl)-1,1-dimethyl urea) was carried out at a glassy carbon anode with ultrasound in order to avoid a total blockage of the electrode surface by a passivating film. The major oxidation product P1 isolated in 23% yield resulted from the loss of one electron and one proton with formation of a nitrogen radical and of the corresponding NN dimer. Two more compounds P2 and P3 were isolated in 12 and 10% yields. They are suggested to originate from an intramolecular Fries rearrangement in dimer P1, i.e. the migration of an amide group from a monomeric unit of the dimer to the aromatic ring of the second one, with formation of a dichloro– N , N –dimethyl benzamide derivative. This rearrangement would be related to a strong adsorption of the intermediate nitrogen radical. It would occur at the positively charged electrode surface concomitantly with the N–N bonding formation. Several non-identified minor compounds were generated, which could involve multi-electron oxidation processes, since the overall oxidation process of diuron required more than one electron. |
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