This paper describes a kinetic model for the decomposition of hydrogen peroxide by ferric ion in homogeneous aqueous solution (pH < 3). The reaction was investigated experimentally at 25.0 °C and I ) 0.1 M (HClO 4 /NaClO 4 ), in a completely mixed batch reactor and under a wide range of experimental conditions (1 e pH e 3; 0.2 mM e [H 2 O 2 ] 0 e 1 M; 50 µM e [Fe(III)] 0 e 1 mM; 1 e [H 2 O 2 ] 0 / [Fe(III)] 0 e 5000). The results of this study demonstrated that the rate of decomposition of hydrogen peroxide by Fe-(III) could be predicted very accurately by a kinetic model which takes into account the rapid formation and the slower decomposition of Fe(III)-hydroperoxy complexes (Fe III -(HO 2 ) 2+ and Fe III (OH)(HO 2 ) + ). The rate constant for the unimolecular decomposition of the Fe(III)-hydroperoxy complexes was determined to be 2.7 × 10 -3 s -1 . The use of the kinetic model allows a better understanding of the effects of operational parameters (i.e., pH and [H 2 O 2 ] 0 / [Fe(III)] 0 ) on the complex kinetics of decomposition of H 2 O 2 by Fe(III).

The kinetics of chlorination of several phenolic compounds and the corresponding formation of chloroform were investigated at room temperature. For the chlorination of phenolic compounds, second-order kinetics was observed, first-order in chlorine, and first-order in the phenolic compound. The rate constants of the reactions of HOCl with phenol and phenolate anion and the rate constant of the acid-catalyzed reaction were determined in the pH range 1-11. The second-order rate constants for the reaction HOCl + phenol varied between 0.02 and 0.52 M(-1) s(-1), for the reaction HOCl and phenolate between 8.46 x 10(1) and 2.71 x 10(4) M(-1) s(-1). The rate constant for the acid-catalyzed reaction varied between 0.37 M(-2) s(-1) to 6.4 x 10(3) M(-2) s(-1). Hammett-type correlations were obtained for the reaction of HOCl with phenolate (log(k) = 4.15-3.00 x sigma sigma) and the acid-catalyzed reaction of HOCl with phenol (log(k) = 2.37-4.26 x sigma sigma). The formation of chloroform could be interpreted with a second-order model, first-order in chlorine, and first-order in chloroform precursors. The corresponding rate constants varied between k > 100 M(-1) s(-1) for resorcinol to 0.026 M(-1) s(-1) for p-nitrophenol at pH 8.0. It was found that the rate-limiting step of chloroform formation is the chlorination of the chlorinated ketones. Yields of chloroform formation depend on the type and position of the substituents and varied between 2 and 95% based on the concentration of the phenol.

The discharge of persistent and mobile organic chemicals (PMOCs) into the aquatic environment is a threat to the quality of our water resources. PMOCs are highly polar (mobile in water) and can pass through wastewater treatment plants, subsurface environments and potentially also drinking water treatment processes. While a few such compounds are known, we infer that their number is actually much larger. This Feature highlights the issue of PMOCs from an environmental perspective and assesses the gaps that appear to exist in terms of analysis, monitoring, water treatment and regulation. On this basis we elaborate strategies on how to narrow these gaps with the intention to better protect our water resources.