ORGANIC INTERMEDIATES IN THE DEGRADATION OF 2,4-DICHLOROPHENOXYACETIC ACID BY FE-3+/H2O2 AND FE-3+/H2O2/UV

The transient products formed during mineralization of 2,4-D by Fe3+-catalyzed hydrogen peroxide in the dark or under 350-nm UV were identified in connection with studies of these advanced oxidation processes for wastewater treatment. Ethyl acetate extracts revealed 2,4-dichlorophenol as the major product (less-than-or-equal-to 15% yield) and less-than-or-equal-to 3% each of 2,4-dichlorophenyl formate, 2,4-dichloro-l-(chloromethoxy)benzene, and 6,8-dichloro-2H-1,4-benzodioxan-3-one. The aqueous phase contained oxalic acid in dark reactions and oxalic and formic acids in photoassisted reactions, identified as their 1-propanol esters. In the light oxalate and formate were found in less-than-or-equal-to 1% yield based on total carbon, but in the dark oxalate accumulated to about 60% yield. Experiment and numerical simulation showed that in the dark oxalate was unreactive toward the oxidizing species (hydroxyl radical) owing to its complexation with ferric ion, while in the light the ferric oxalate complex photolyzes to CO2.