The Mechanisms, Products, and Kinetics of Triclosan-Free Chlorine Reactions

Abstract

The kinetics, products, and reaction pathways of triclosan/free chlorine reactions were investigated for the pH range 3.5-11. Although pH dependent speciation occurs in both triclosan and free chlorine, only the reaction between HOCl and the phenolate-triclosan was found to play a significant role in the kinetics. The second order rate constant for the reaction between phenolate-triclosan and HOCl was found to be 5.40 (±1.82) Ã 103 M⁻¹s⁻¹. Three chlorinated triclosan intermediates were tentatively identified based on mass spectral analysis. Additionally, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and chloroform formed under excess free chlorine conditions. The majority of the chloroform formed during the reactions does not form via 2,4-dichlorophenol and 2,4,6-trichlorophenol oxidation. Therefore, the majority of chloroform is likely formed via the oxidation of triclosan's phenolic ring. Based on the identified products, a reaction pathway was proposed for the oxidation of triclosan in the presence of free chlorine.