Oxidation of estrone by aqueous permanganate: reaction kinetics and oxidation products

The purpose of this article was to investigate the effectiveness and mechanism for the oxidation of estrone by aqueous potassium permanganate. Experiments were conducted to examine the reaction kinetics of potassium permanganate with estrone under the condition with potassium permanganate in excess over a wide pH range. Then, reaction products of estrone with potassium permanganate were identified with liquid chromatography tandem mass spectrometry (LC-MS/MS). The results showed that the loss of estrone followed the pseudo-first-order kinetics with potassium permanganate, suggesting that the reaction is first-order with respect to estrone. The pseudo-first-order rate constant (K_obs, s^-1) increased linearly with the increase of potassium permanganate concentration. The degradation of estrone of the second-order rate constants (k, L·mol^-1·s^-1) increased with the increase of pH. Estrone was shown to exhibit similarly appreciable reactivity toward potassium permanganate with the second-order rate constant at near neutral pH comparable to chlorine but much lower than that of ozone. In comparison with these oxidants, however, potassium permanganate was much more effective for the oxidative removal of estrone in real waters, mainly due to the relatively high stability of potassium permanganate therein. Identification of oxidation products suggested the initial attack of potassium permanganate at the hydroxyl group in the aromatic ring of estrone, leading to the formation of a series of quinone-like and aromatic ring-opening products and thus the elimination of its estrogenic activity.