The photolysis of phenol and its derivatives received great attention due to their widespread occurrence in surface waters as organic contaminants and as important moieties in humic substances. Very recent studies showed that the irradiation of some phenols generate OH radicals in the fisrt stage of the reaction and featureless long-wavelength absorbing compounds exhibiting sensitizing properties at higher extent. Due to the strong interest in such reactions for understanding the fate of organic contaminants in the aquatic environment, we undertook a comprehensive investigation of the long term photochemical transformation (simulated solar light) of two substituted phenols: 5-halogenosalicylic acids (5-ClSA and 5-BrSA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). By means of laser flash photolysis, steady-state irradiation, photoproducts identification by high resolution mass spectrometry (HRMS) and quantum calculations, we were able to establish the primary reaction mechanism. Excitation of monoanionic 5-ClSA and 5-BrSA generates the triplet carbene by dehalogenation of the long-lived triplet excited state. Upon formation, this highly reactive carbene reacts with water, oxygen and its precursors to yield 2,5-DHBA and other primary photoproducts. Secondary reaction pathways leading to mineralization were investigated by HRMS analysis of solutions irradiated at various stages of the transformation, before and after derivatization with DNPH (dinitro phenyl hydrazine) and BSTFA (N,O-Bistrifluoroacetamide), TOC measurement, and OH radical scavenging technique. Numerous photoproducts from C<sub>2</sub> to C<sub>19</sub> were identified. As a key result, the formation of light induced secondary OH (LIS-OH) precursors could be demonstrated. These data shed light on the fate of irradiated organic compounds, on the formation of OH radical from humic-like light absorbing compounds or non-absorbing molecules and on the changes over time of irradiated light absorbing compounds.

Photomineralization of 5-halogenosalicylic acids: A self-sustained reaction via the formation of Light Induced Secondary OH precursors (LIS-OH)

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.