Degradation of 4-aminoantipyrine by electro-oxidation with a boron-doped diamond anode: Optimization by central composite design, oxidation products and toxicity.

Electro-oxidation with electrogenerated H 2 O 2 (EO-H 2 O 2 ) was applied to treat acidic aqueous solutions of 4-aminoantipyrine (4-AA), a persistent drug metabolite of dipyrone, in sulfate medium. Trials were made using a boron-doped diamond anode in the presence of H 2 O 2 electrogenerated on site. A 2 4 central composite design (CCD) was employed to evaluate the effect of four independent variables, namely current density ( j ), pH, 4-AA concentration and electrolysis time, on the percentages of degradation and mineralization, as well as on mineralization current efficiency (MCE). Predicted responses agreed with observed values, showing linear trendlines with good R 2 and R 2 adj values. The degradation was optimum at j = 77.5 mA cm −2 , pH 3.5 and 62.5 mg L −1 4-AA, leading to 63% and 99% removal after 3 and 7 min, respectively. For those solutions, the largest mineralization was found at j = 77.5 mA cm −2 , attaining 45% abatement at 175 min. Low MCE values were obtained in all electrolyses. An initial route for 4-AA degradation is proposed based on one dimer and eleven aromatic and aliphatic intermediates detected in the treated solutions at pH 3.5 by LC-MS. The initial 62.5 mg L −1 solution at pH 3.5 presented acute toxicity on Artemia salina larvae, with LC 50 = 13.6 mg L −1 , being substantially reduced after 3 and 7 min of EO-H 2 O 2 at j = 77.5 mA cm −2 due to the formation of less toxic derivatives. [ABSTRACT FROM AUTHOR]