The solvent-dependence of the degradation of para-aminobenzoic acid (PABA) and 2-ethylhexyl 4-(dimethylamino)benzoate (padimate-O) due to UV-radiation is investigated. Both compounds are used as UV-absorbers in personal care products, and are emerging environmental contaminants. The variation in solvent environments between personal care products and aqueous environmental conditions makes it important to understand how solvent conditions can impact the UV-degradation of these compounds. Quantum yields for PABA and padimate-O are evaluated in methanol, acetonitrile, and dichloromethane. The highest quantum efficiencies are observed in the aprotic solvents. PABA and Padimate-O are irradiated with UVA light in methanol and acetonitrile, and the absorbance spectra are collected at various time points over approximately 24 h. The absorbance at the initial wavelength of max absorbance decreased through the exposure, and a new peak concurrently grew in at a lower wavelength. This indicates UV-induced photodegradation of PABA and padimate-O results in the formation of new photoproduct(s). High performance liquid chromatography (HPLC) is used to separate the photoproducts resulting from irradiation from the parent compound and isolate the spectral changes of the photoproduct. Liquid chromatography mass spectrometry (LCMS) utilizing similar separation conditions is used to identify masses of the individual photoproducts, and tandem mass spectrometry allows inference of the molecular structure of the photoproducts. The combined spectroscopic and chromatography analysis provides means to assess the solvent-dependent degradation kinetics and propose reaction mechanisms.

Solvent effects on the quantum efficiencies and UV-induced photodegradation of PABA and padimate-O

251st National Meeting (2016)

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