Degradation kinetics and chloropicrin formation during aqueous chlorination of dinoseb

The kinetics of chlorination of dinoseb and the corresponding formation of disinfection by-products (DBPs) were studied between pH 4 and 9 at room temperature (25 +/- 1 degrees C). The reactivity shows a minimum at pH 9, a maximum at pH 4 and a medium at neutral conditions. pH profile of the apparent second-order rate constant of the reaction of dinoseb with chlorine was modeled considering the elementary reactions of HOCl with dinoseb species and an acid-catalyzed reaction. The predominant reactions at near neutral pH were the reactions of HOCl with the two species of dinoseb. The rate constants of 2.0 (+/- 0.8) x 10(4) M-2 s(-1), 3.3 (+/- 0.6) and 0.5 (+/- 0.1) M-1 s(-1) were determined for the acid-catalyzed reaction, HOCl reacted with dinoseb and dinoseb(-), respectively. The main degradation by-products of the dinoseb formed during chlorination have been separated and identified by GC-MS with liquid-liquid extraction sample pretreatment. Six volatile and semi-volatile DBPs were identified in the chlorination products, including chloroform (CF), monochloroacetone, chloropicrin (TCNM), 1,1-dichloro-2-methy-butane, 1,2-dichloro-2-methy-butane, 1-chloro-3-methy-pentanone. A proposed degradation pathway of dinoseb during chlorination was then given. TCNM and CF formation potential during chlorination of dinoseb reached as high as 0.077 and 0.0971 mu M mu M-1 dinoseb under the traditional condition (pH = 7 and Cl-2/C = 2). Their yields varied with Cl-2/C, pH and time. The maximum yields of TCNM appeared at molar ratio as Cl-2/C = 1 and pH 3, while the maximum of CF appeared at molar ratio as Cl-2/C = 4 and pH 7. [TCNM]/[CF] decreased with reaction time and increased solution pH. (C) 2013 Elsevier Ltd. All rights reserved.