Formation of chlorinated breakdown products during degradation of sunscreen agent, 2-ethylhexyl-4-methoxycinnamate in the presence of sodium hypochlorite.

Alicja Gackowska,Waldemar Studziński,Maciej Przybyłek,Jerzy Gaca

doi:10.1007/s11356-015-5444-0

Abstract

In this study, a new degradation path of sunscreen active ingredient, 2-ethylhexyl-4-methoxycinnamate (EHMC) and 4-methoxycinnamic acid (MCA) in the presence of sodium hypochlorite (NaOCl), was discussed. The reaction products were detected using gas chromatography–mass spectrometry (GC-MS). Since HOCl treatment leads to more polar products than EHMC, application of polar extracting agents, dichloromethane and ethyl acetate/n-hexane mixture, gave better results in terms of chlorinated breakdown products identification than n-hexane. Reaction of EHMC with HOCl lead to the formation of C=C bridge cleavage products such as 2-ethylhexyl chloroacetate, 1-chloro-4-methoxybenzene, 1,3-dichloro-2-methoxybenzene, and 3-chloro-4-methoxybenzaldehyde. High reactivity of C=C bond attached to benzene ring is also characteristic for MCA, since it can be converted in the presence of HOCl to 2,4-dichlorophenole, 2,6-dichloro-1,4-benzoquinone, 1,3-dichloro-2-methoxybenzene, 1,2,4-trichloro-3-methoxybenzene, 2,4,6-trichlorophenole, and 3,5-dichloro-2-hydroxyacetophenone. Surprisingly, in case of EHMC/HOCl/UV, much less breakdown products were formed compared to non-UV radiation treatment. In order to describe the nature of EHMC and MCA degradation, local reactivity analysis based on the density functional theory (DFT) was performed. Fukui function values showed that electrophilic attack of HOCl to the C=C bridge in EHMC and MCA is highly favorable (even more preferable than phenyl ring chlorination). This suggests that HOCl electrophilic addition is probably the initial step of EHMC degradation.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-015-5444-0) contains supplementary material, which is available to authorized users.

Highlights

Sodium hypochlorite is one of the most commonly used disinfectants in water treatment
Many studies have been focused on purely anthropogenic halogenated disinfection by-products (HDBPs) (Negreira et al 2008; Nakajima et al 2009; Santos et al 2013; Solakyildirim et al 2014; Bulloch et al 2015) which can be formed through pharmaceuticals and personal
In order to evaluate the effect of hypochlorous acid (HOCl) on the stability and photostability of EHMC, gas chromatography–mass spectrometry (GC-MS) analyses of reaction mixtures were performed

Summary

Introduction

Sodium hypochlorite is one of the most commonly used disinfectants in water treatment. It has been reported that EHMC undergoes degradation in the presence of UV light and different oxidizing and chlorinating agents (Nakajima et al 2009; MacManusSpencer et al 2011; Gackowska et al 2014), there is no comprehensive report dealing with the formation of EHMC chlorinated breakdown products under the water chlorination conditions This is a complex issue, since there are many factors which can affect degradation of UV filters such as sunlight radiation, pH, and dissolved organic and inorganic compounds (Sakkas et al 2003, Nakajima et al 2009; Jammoul et al 2009; Zhang et al 2010; Zhou et al 2013). In order to gain better insight into this question, experimental results were supported with Fukui function value analysis

Materials and methods

Results and discussion

Conclusions