Kinetics and mechanism of the reaction of hydrogen peroxide with hypochlorous acid: Implication on electrochemical water treatment

Reduction of HOCl to Cl by in-situ electrochemical synthesis or ex-situ addition of H2O2 is a feasible method to minimize Cl-DBPs and ClOx- (x = 2, 3, and 4) formation in electrochemical oxidative water treatment systems. This work has investigated the kinetics and mechanism of the reaction between H2O2 and HOCl. The kinetics study showed the species-specific second order rate constants for HOCl with H2O2 (k(1)), HOCl with HO2 (k(2)) and OCl with H2O2 (k(3)) are 195.5 +/- 3.3 M 1s 1, 4.0 x 10(7) M(-1)s(-1) and 3.5 x 10(3) M 1s 1, respectively. The density functional theory calculation showed k(2) is the most advantageous thermodynamically pathway because it does not need to overcome a high energy barrier. The yields of O-1(2) generation from the reaction of H2O2 with HOCl were reinvestigated by using furfuryl alcohol (FFA) as a probe, and an average of 92.3% of O-1(2) yields was obtained at pH 7-12. The second order rate constants of the reaction of O-1(2) with 13 phenolates were determined by using the H2O2/HOCl system as a quantitative O-1(2) production source. To establish a quantitative structure activity relationship, quantum chemical descriptors were more satisfactory than empirical Hammett constants. The potential implications in electrochemical oxidative water treatment were discussed at the end.

Automated summary

This study investigated the kinetics and mechanism of the reaction between H2O2 and HOCl, and discussed the potential implications in electrochemical oxidative water treatment.