General-acid-catalyzed reactions of hypochlorous acid and acetyl hypochlorite with chlorite ion

The rate of oxidation of ClO2- by HOCl is first order in each reactant and is general-acid catalyzed. In the initial steps of the proposed mechanism, a steady-state intermediate, HOClOClO-, forms (k(1) = 1.6 M-1 s(-1)) and un dergoes general-acid (HA)-catalyzed reactions (k(2)(HA)) to generate a meta stable intermediate, ClOClO. Values of k(2)(HA)/k(-1) are 1.6 x 10(4) M-1 ( H3O+), 20 M-1 (HOAc), and 8.5 M-1 (H2PO4-). Subsequent competitive reaction s of ClOClO with ClO2- (k(3)) to give 2ClO(2) and with OH- (k(4)(OH)) and o ther bases (k(5)(B)) to give ClO3- are very rapid. The relative yields of t hese products give k(4)(OH)/k(3) = 1.3 x 10(5), k(5)(HPO4)/k(3) = 0.20, and k(5)(OAc)/k(3) = 0.06. At low pH and low buffer concentrations, the appare nt yield of ClO2, based on 2ClO(2) per initial HOCl, reaches 140%. This ano maly is attributed to the induced disproportionation of ClO2- by ClOClO to give ClO3- and additional HOCl. A highly reactive intermediate, ClOCl(O)OCl O-, is proposed that can undergo Cl-O bond cleavage to give 2ClO(2) + Cl- v ia one path and ClO3- + 2HOCl via another path. The additional HOCl recycle s in the presence of excess ClO2- to give more ClO2. Ab initio calculations show feasible structures for the proposed reaction intermediates. Acetic a cid has a second catalytic role through the formation of acetyl hypochlorit e, which is much more reactive than HOCl in the transfer of Cl+ to ClO2- to form ClOClO.