Experimental and theoretical studies on the photodegradation of 2-ethylhexyl 4-methoxycinnamate in the presence of reactive oxygen and chlorine species

TL;DR

This study combines experimental and theoretical approaches to investigate the photodegradation pathways of the sunscreen ingredient EHMC in the presence of reactive oxygen and chlorine species, identifying key reaction products and their thermodynamic favorability.

Contribution

It provides new insights into the photodegradation mechanisms of EHMC using GC-MS analysis and quantum chemical calculations, highlighting the formation of specific chloro-organic compounds.

Findings

Chloro-substituted degradation products identified by GC-MS.

Reactions with Cl2 and HOCl are thermodynamically favorable.

Reactivity indices explain formation of specific chloro-organic compounds.

Abstract

2-Ethylhexyl 4-methoxycinnamate (EHMC) is one of the most commonly used sunscreen ingredient. In this study we investigated photodegradation of EHMC in the presence of such common oxidizing and chlorinating systems as H2O2, H2O2/HCl, H2O2/UV, and H2O2/HCl/UV. Reaction products were detected by gas chromatography with a mass spectrometric detector (GC-MS). As a result of experimental studies chloro-substituted 4-methoxycinnamic acid (4-MCA), 4-methoxybenzaldehyde (4-MBA) and 4-methoxyphenol (4-MP) were identified. Experimental studies were enriched with DFT and MP2 calculations. We found that reactions of 4-MCA, 4-MBA and 4-MP with Cl2 and HOCl were in all cases thermodynamically favorable. However, reactivity indices provide a better explanation of the formation of particular chloroorganic compounds. Generally, those isomeric forms of mono- and dichlorinated compounds which exhibits the highest hardness were identified. Nucleophilicity of the chloroorganic compounds precursors were examined by means of the Fukui function.