  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.
