Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

Abstract

The photolysis of pesticides with different fluorine motifs was evaluated to quantify the formation of fluorinated products in buffered aqueous systems, advanced oxidation (AOP) and reduction processes (ARP), and river water. Simulated sunlight quantum yields at pH 7 were 0.0033, 0.0025, 0.0015, and 0.00012 for penoxsulam, florasulam, sulfoxaflor, and fluroxypyr, respectively. The bimolecular rate constants with hydroxyl radicals were 2 to 5.7 × 10 10 M −1 s −1 and, with sulfate radicals, 1.6 to 2.6 × 10 8 M −1 s −1 for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100fold lower. Using quantitative 19 F-NMR, complete fluorine mass balances were obtained. The maximum fluoride formation was 53.4 and 87.4% for penoxsulam and florasulam under ARP conditions, and 6.1 and 100% for sulfoxaflor and fluroxypyr under AOP conditions. Heteroaromatic CF 3 and aliphatic CF 2 groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF 3 and CF 2 groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. 19 F-NMR chemical shifts and coupling analysis provided information on hydrogen loss on adjacent bonds or changes in chirality. Mass spectrometry results were consistent with the observed 19 F-NMR products. These results will assist in selecting treatment processes for specific fluorine motifs and in the design of agrochemicals to reduce byproduct formation.

Wavelength-Dependent UV-LED Photolysis of Fluorinated Pesticides and Pharmaceuticals

“…The products indicated a loss of one or both stereocenters from the parent based on differences in peak splitting, but the Het-CF 3 is retained, irrespective of the wavelength . The LC–HRMS results agree with products observed in the solar simulator in our previous study . Fluoride and the maximum amount of TFA of all wavelengths was only observed for 308 nm, but yields were only 14.9 and 10.7%, respectively.…”

“…Fluorinated photoproducts may be of environmental concern due to their potential persistence and toxicity. It has been reported that total fluorine mass balances often fall short during nontarget liquid chromatography high-resolution mass spectrometry (LC–HRMS) product identification. − Our previous works have established a rapid, reliable, and reproducible detection method to quantify and screen fluorinated products in photolyzed solutions using fluorine nuclear magnetic resonance spectroscopy ( 19 F NMR). , Previous studies have shown that 19 F NMR analysis can identify products and complement LC–HRMS results. , Our previous study reported photoproduct formation from four fluorinated pesticides using 19 F NMR and LC–HRMS, but photolysis of more fluorinated compounds needs to be studied to understand the effect of fluorinated motifs in the structure . Fluorine motifs could form fluoride, trifluoroacetic acid (TFA), or persistent fluorinated products, and the dependence of fluorine motifs on the photolysis wavelength needs to be identified for potential optimized design and synthesis of fluorinated compounds.…”

Fluorous Liquids for Magnetic Resonance-Based Thermometry with Enhanced Responsiveness and Environmental Degradation

“…The F − peak for ozonation is shifted slightly upfield compared to that of photolysis, but it was deemed the F − peak because of the broad signal and sensitivity to solvent composition commonly seen experimentally in our previous work. 32,33 While F − production is believed to be from the aromatic fluorines as previously demonstrated, not all of the Ar-F can be accounted for via F − . 32,33 This is supported by the sum of the concentrations of fluorine for Ar-F, F − , and ringopening products/vinyl fluorine being 198 μM and 200 μM for photolysis and O 3 , respectively.…”

Photodegradation of polyolefin thin films in simulated freshwater conditions

“…Additionally, similar results have been found through indirect photolysis studies of a variety of different pollutants, 60 such as pesticides where DOM generated 3DOM, ˙OH, and 1 O 2 contributed at varying percent to the degradation of these molecules. 61,62…”

“…Additionally, similar results have been found through indirect photolysis studies of a variety of different pollutants, 60 such as pesticides where DOM generated 3DOM, cOH, and 1 O 2 contributed at varying percent to the degradation of these molecules. 61,62 We further tested the difference between freshwater and saltwater conditions, repeating photolysis experiments under simulated ocean conditions without the presence of DOM (i.e., "Instant Ocean" solution), resulting in no signicant carbonyl signal (ESI Fig. S5 †).…”