Separation and Purification Technology 67 (2009) 141–148 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Kinetic and mechanistic investigation of the ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution Amilcar Machulek Jr. a,b,d,e , Eliso Gogritchiani b , José E.F. Moraes c,d , Frank H. Quina a,d , André M. Braun b , Esther Oliveros b,∗ a Instituto de Química, Universidade de São Paulo, CP 26077, São Paulo 05513-970, Brazil b Lehrstuhl für Umweltmesstechnik, Universität Karlsruhe, D-76128 Karlsruhe, Germany c Escola Paulista de Engenharia Química, Universidade Federal de São Paulo, 09972-270 Diadema, Brazil d Centro de Capacitac ¸ão e Pesquisa em Meio Ambiente (CEPEMA-USP), Universidade de São Paulo, 11730-000 Cubatão, Brazil e Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados, Mato Grosso do Sul - MS, 79804-970, Brazil article info Keywords: Ozonolysis 2,4-Xylidine (2,4-dimethyl-aniline) Kinetics Mechanisms Fenton reaction abstract The ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution was investigated by determining the major reaction products and their evolution as a function of the reaction time and their dependence on the pH of the reaction system. 2,4-Dimethyl-nitrobenzene and 2,4-dimethyl-phenol were found to be primary reaction products; their formation might be explained by electron transfer and substitution reactions. 2,4-Dimethyl-phenol was further oxidized yielding 2,4-dimethyl- and/or 4,6- dimethyl-resorcinol by electrophilic addition of HO • radicals. The best fitting phenomenological kinetic model and the good convergence of calculated and experimentally determined rate constants imply two additional competitive pathways of substrate oxidation: (i) electrophilic addition of HO • radicals and fast subsequent substitution would also yield the resorcinol derivatives. (ii) Substrate and isolated products are thought to be oxidized by hydrogen abstraction at the benzylic sites, but the corresponding prod- ucts (alcohols, aldehydes, and carboxylic acids) could not be identified. Fe(II) was added to probe for the presence of H 2 O 2 , but had no or only a minor effect on the kinetics of the ozonolysis. © 2009 Elsevier B.V. All rights reserved. 1. Introduction 2,4-Xylidine (2,4-dimethyl-aniline) is a well-known pollutant present in industrial wastewaters [1]. In addition, it has been found to be a very convenient model pollutant for mechanistic investi- gations in the domain of thermal and photochemical methods of oxidative degradation (AOP), such as VUV-photolysis [2] and ther- mal and photochemically enhanced Fenton reactions [3,4]. Product analysis of the latter allowed to differentiate between a hydroxyl radical (HO • ) initiated oxidation and an oxidation by a higher valent iron species, e.g. ferryl (Fe(IV)) [5]. Ozone (O 3 ) is frequently used as an oxidant for the abiotic treat- ment of wastewaters [6]. The oxidative degradation of 2,4-xylidine was already investigated for process development [7], but in the present work, 2,4-xylidine is used as a model pollutant in order (i) to study the reaction paths of its oxidation by ozone (O 3 ) as well as (ii) to estimate the extent of the reaction of ozone with the acidic aqueous solution, producing hydrogen peroxide (H 2 O 2 ). Genera- ∗ Corresponding author. Permanent address: Laboratoire IMRCP, UMR CNRS 5623, Université Paul Sabatier, F-31062 Toulouse Cédex 9, France. E-mail address: oliveros@chimie.ups-tlse.fr (E. Oliveros). tion of HO • radicals may be enhanced in the presence of Fe(II) ions, and the Fenton reaction could be used to probe the production of H 2 O 2 under the given experimental conditions. Kinetic investiga- tions are coupled with model calculations to assess a scheme of reactions based on the evolution of the initial oxidation products. 2. Materials and methods 2.1. Chemicals Iron(II) perchlorate hydrate (Fe(ClO 4 ) 2 ·6H 2 O) 98%, 2,4- dimethyl-aniline (2,4-xylidine. 2,4-XY) +99%, 2,4-dimethyl-phenol (2,4-DMP) 98%, 2,4-dimethyl-1-nitrobenzene (2,4-DMNB) +99%, perchloric acid (HClO 4 ), all from Sigma–Aldrich, Steinheim, Germany, and anhydrous calcium chloride, (CaCl 2 ) +97%, Fluka, Steinheim, Germany, were used as received. 2.2. Preparation of solutions Solutions were prepared with H 2 O of tridistilled quality (UHQ- II). The concentrations of 2,4-XY, 2,4-DMP and 2,4-DMNB solutions were 5.0, 5.0 and 1.0mM, respectively. 1383-5866/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.03.024