Catalytic oxidative degradation of 17α-ethinylestradiol by FeIII-TAML/H2O2: Estrogenicities of the products of partial, and extensive oxidation

Abstract

The oxidative degradation of the oral contraceptive 17α-ethinylestradiol (EE2) in water by a new advanced catalytic oxidation process was investigated. The oxidant employed was hydrogen peroxide in aqueous solution and the catalyst was the iron tetra-amido macrocyclic ligand (FeIII-TAML) complex that has been designated Na[Fe(H2O)(B*)] (FeIII-B*). EE2 (10 μM) was oxidised rapidly by the FeIII-B*/H2O2 (5 nM/4 mM) catalytic oxidation system at 25 °C, and for reactions at pH 8.40–11.00, no unchanged EE2 was detected in the reaction mixtures after 60 min. No oxidation of EE2 was detected in blank reactions using either H2O2 or FeIII-B* alone. The maximum rate of EE2 loss occurred at pH 10.21. At this pH the half-life of EE2 was 2.1 min and the oxidised products showed around 30% estrogenicity removal, as determined by the yeast estrogen screen (YES) bioassay. At pH 11.00, partial oxidation of EE2 by FeIII-B*/H2O2 (5 nM/4 mM) was studied (half-life of EE2 was 14.5 min) and in this case the initial intermediates formed were a mixture of the epimers 17α-ethynyl-1,4-estradiene-10α,17β-diol-3-one (1a) and 17α-ethynyl-1,4-estradiene-10β,17β-diol-3-one (1b) (identified by LC-ToF-MS and 1H NMR spectroscopy). Significantly, this product mixture displayed a slightly higher estrogenicity than EE2 itself, as determined by the YES bioassay. Upon the addition of further aliquots of FeIII-B* (to give a FeIII-B* concentration of 500 nM) and H2O2 (to bring the concentration up to 4 mM assuming the final concentration had dropped to zero) to this reaction mixture the amounts of 1a and 1b slowly decreased to zero over a 60 min period as they were oxidised to unidentified products that showed no estrogenicity. Thus, partial oxidation of EE2 gave products that have slightly increased estrogenicity, whereas more extensive oxidation by the advanced catalytic oxidation system completely removed all estrogenicity. These results underscore the importance of controlling the level of oxidation during the removal of EE2 from water by oxidative processes.