Oxidation of diclofenac with ozone in aqueous solution

Ozonation of diclofenac in aqueous solution in the presence and absence of an (OH)-O-center dot scavenger, tertiary butanol (t-BuOH),was studied, and the most important reaction intermediates and products were identified. The second-order O-3 rate constant was determined by competition with buten-3-ol and was found to be 6.8 x 10(5) M-1 s(-1) at 20 degrees C. From this high rate constant, it has been concluded that O-3 must initially add on the amino nitrogen. Decomposition of the adduct results in the formation Of O-3(center dot-) (-> center dot OH) and aminyl radical precursors. A free (OH)-O-center dot yield of 30% was estimated based on the HCHO yields generated upon reaction of (OH)-O-center dot with 0.01 M t-BuOH. Almost all diclofenac reacted when the molar ratio of O-3/diclofenac was similar to 5:1 in the presence of t-BuOH and similar to 8:1 in its absence. As primary reaction products (maximum yield), diclofenac-2,5-iminoquinone (32%), 5-hydroxydiclofenac (7%), and 2,6-dichloroaniline (19%) were detected with respect to reacted diclofenac in the presence of t-BuOH. These primary products degraded into secondary ones when the O-3 dose was increased. In the (OH)-O-center dot-mediated reaction (absence of t-BuOH) small yields of 5-hydroxydiclofenac (4.5%), diclofenac-2,5-iminoquinone (2.7%), and 2,6-dichloroaniline (6%) resulted. Practically all Cl- (95%) was released in the absence of t-BuOH but only about 45% in the presence of t-BuOH at an O-3/diclofenac molar ratio of 10:1. Based on the reaction products, mechanisms that may account for the high O-3 consumption during ozonation of diclofenac are suggested. For technical applications, adequate supply of O-3 is needed not only to eliminate diclofenac, but also for the degradation of its potentially toxic products like diclofenac-2,5-iminoquinone and 5-hydroxydiclofenac.