A Series of Deoxyfluorination Reagents Featuring OCF2 Functional Groups

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Marine Transport Barrier for Traditional and Emerging Per- and Polyfluoroalkyl Substances in the Southeast Indian Ocean and Antarctic Marginal Seas

Traditional per- and polyfluoroalkyl substances (PFASs) have been observed in the remote Southern Ocean. In contrast, current knowledge about emerging PFASs, such as perfluoroether carboxylic acids (PFECAs), and their transport mechanisms remains ambiguous. In this study, the occurrence and transport of both traditional and emerging PFASs in the surface seawater of the Southeast Indian Ocean and Antarctic marginal seas are comprehensively discussed by integrating hydrological data. Long-chain PFASs were restricted to the north of the thermohaline front in the Southeast Indian Ocean, suggesting a transport barrier effect and the input of terrestrial contamination from low-latitude regions. Conversely, unexpectedly high levels of short-chain perfluorobutanoic acid (PFBA) were limited to the south of the Antarctic Circumpolar Current, preventing further northward transport. PFBA showed significant positive correlations with two emerging PFECAs, perfluoro-2-methoxyacetic acid (PFMOAA) and fluoro(heptafluoropropoxy)acetic acid (3:2 H-PFECA), which were also widely detected in Antarctic marginal seas for the first time. This suggests their similar sources and environmental behavior, as they were probably formerly accumulated in Antarctic snow through atmospheric deposition and released into seawater during the summertime melting process.

Electrochemical Decarboxylative Cross-Coupling with Nucleophiles

Decarboxylative cross-coupling reactions are powerful tools for carbon-heteroatom bonds formation, but typically require pre-activated carboxylic acids as substrates or heteroelectrophiles as functional groups. Herein, we present an electrochemical decarboxylative cross-coupling of carboxylic acids with structurally diverse fluorine, alcohol, H2O, acid, and amine as nucleophiles. This strategy takes advantage of the ready availability of these building blocks from commercial libraries, as well as the mild and oxidant-free conditions provided by electrochemical system. This reaction demonstrates good functional-group tolerance and its utility in late-stage functionalization.

Recent Advances in the Synthesis and Transformation of Carbamoyl Fluorides, Fluoroformates, and Their Analogues

Carbamoyl fluorides, fluoroformates, and their analogues are a class of important compounds and have been evidenced as versatile building blocks for the preparation of useful molecules in organic chemistry. While major achievements were made in the synthesis of carbamoyl fluorides, fluoroformates, and their analogues in the last half of 20th century, an increasing number of reports have focused on using O/S/Se=CF2 species or their equivalents as the fluorocarbonylation reagents for the direct construction of these compounds from the parent heteroatom-nucleophiles in recent years. This review mainly summarizes the advances in the synthesis and typical application of carbamoyl fluorides, fluoroformates, and their analogues by the halide exchanges and fluorocarbonylation reactions since 1980.

Emerging and Legacy Perfluoroalkyl Substances in Breastfed Chinese Infants: Renal Clearance, Body Burden, and Implications

BACKGROUND

Human breast milk is a primary route of exposure to perfluoroalkyl substances (PFAS) in infants. To understand the associated risks, the occurrence of PFAS in human milk and the toxicokinetics of PFAS in infants need to be addressed.

OBJECTIVES

We determined levels of emerging and legacy PFAS in human milk and urine samples from Chinese breastfed infants, estimated renal clearance, and predicted infant serum PFAS levels.

METHODS

In total, human milk samples were collected from 1,151 lactating mothers in 21 cities in China. In addition, 80 paired infant cord blood and urine samples were obtained from two cities. Nine emerging PFAS and 13 legacy PFAS were analyzed in the samples using ultra high-performance liquid chromatography tandem mass spectrometry. Renal clearance rates (CLrenals) of PFAS were estimated in the paired samples. PFAS serum concentrations in infants (<1 year of age) were predicted using a first-order pharmacokinetic model.

RESULTS

All nine emerging PFAS were detected in human milk, with the detection rates of 6:2 Cl-PFESA, PFMOAA, and PFO5DoDA all exceeding 70%. The level of 6:2 Cl-PFESA in human milk (median concentration=13.6 ng/L) ranked third after PFOA (336 ng/L) and PFOS (49.7 ng/L). The estimated daily intake (EDI) values of PFOA and PFOS exceeded the reference dose (RfD) of 20 ng/kg BW per day recommended by the U.S. Environmental Protection Agency in 78% and 17% of breastfed infant samples, respectively. 6:2 Cl-PFESA had the lowest infant CLrenal (0.009mL/kg BW per day), corresponding to the longest estimated half-life of 49 y. The average half-lives of PFMOAA, PFO2HxA, and PFO3OA were 0.221, 0.075, and 0.304 y, respectively. The CLrenals of PFOA, PFNA, and PFDA were slower in infants than in adults.

CONCLUSIONS

Our results demonstrate the widespread occurrence of emerging PFAS in human milk in China. The relatively high EDIs and half-lives of emerging PFAS suggest potential health risks of postnatal exposure in newborns. https://doi.org/10.1289/EHP11403.

Divergent dehydroxyfluorination and carbonation of alcohols with trifluoromethyl trifluoromethanesulfonate

Preparation of alkyl fluorides and carbonates via divergent dehydroxyfluorination and carbonation of alcohols with trifluoromethyl trifluoromethanesulfonate (CF₃SO₂OCF₃) is described. The reactions performed with BTMG in THF provided alkyl fluorides in good yields, whereas those of two different alcohols with Et₃N in DCM formed asymmetric carbonates in moderate to excellent yields. CF₃SO₂OCF₃ was demonstrated to be either a "F" or a "CO" reagent in the reactions by changing the base, allowing the selective construction of alkyl fluorides and carbonates from the corresponding alcohols with high efficiency. Notably, the fluorine-containing asymmetric carbonates that are difficult to synthesize by other methods were comprehensively prepared by this method, which would have great application potential in both academic and industrial fields.

Vital Environmental Sources for Multitudinous Fluorinated Chemicals: New Evidence from Industrial Byproducts in Multienvironmental Matrices in a Fluorochemical Manufactory

Direct emissions from fluorochemical manufactory are an important source of per- and polyfluoroalkyl substances (PFASs) to the environment. In this study, a wide range of PFASs, including 8 legacy PFASs, 8 long-chain perfluoroalkyl carboxylic acids (PFCAs), and 40 emerging PFASs, were investigated through a target screening in multienvironmental matrices from a fluorochemical manufactory in China. Indoor dust was the most polluted matrix, wherein 52 PFASs were detected, and the median concentration of long-chain PFCA was 276 ng/g. A high level of short-chain PFAS in total suspended particles (median concentration = 416 ng/m³) and the effluent in the manufactory (Σ₄₈PFAS = 212 μg/L) will undoubtedly increase the burden on the surrounding environment. Twenty-four industrial byproducts were ascertained to be generated during the electrochemical fluorination (ECF) process, and eight fluorinated alternatives were considered to be produced during product development. Twelve PFASs were quantified for the first time in the working environments. Perfluoropropane sulfonic acid, perfluoro (2-ethoxyethane) sulfonic acid (PFEESA), and 2-perfluorohexyl ethanoic acid are abundant fluorinated alternatives, with median levels of 1187-17204 ng/g in the dust. Significant positive correlations between ECF-related PFAS products and byproducts indicate that the detected values are strongly connected with the industrial source. Hierarchical cluster analysis further manifests their affiliation. Our findings raise the need for further investigations of emerging PFAS (including the first report of PFAS, such as PFEESA, in the environment) which may be released during the production process in the fluorochemical manufactories.

Nontargeted Identification and Temporal Trends of Per- and Polyfluoroalkyl Substances in a Fluorochemical Industrial Zone and Adjacent Taihu Lake

Various per- and polyfluoroalkyl substances (PFASs) remain undiscovered and unexplored in the environment. The goals of this study were to discover new species of PFASs in effluent and surface waters from a fluorochemical industrial zone, and to assess their concentration, distribution, and temporal trends in the adjacent natural environment. In total, 83 emerging PFASs from 14 classes were identified, 22 of which were reported for the first time. Authentic standards were synthesized for 13 per- and polyfluoroalkyl ether carboxylic acids (PFECAs), thereby greatly expanding the scope of PFAS-targeted monitoring. The newly identified compounds accounted for 27%-95% of the total PFAS concentrations. Of note, a novel diether carboxylic acid, 2-[2-(trifluoromethoxy)hexafluoropropoxy]tetrafluoropropanoic acid (C7 HFPO-TA) was detected at an extremely high concentration in the fluorochemical zone effluent (447 000 ng/L) and at a median concentration in the fluorochemical zone surface water (670 ng/L), with detectable levels also found in the natural environment, that is, Wangyu River (23 ng/L) and Taihu Lake (5.6 ng/L). The distinct geographic distribution of C7 HFPO-TA suggests transport from the industrial point source to Taihu Lake via the Wangyu River. The concentration of C7 HFPO-TA in Taihu Lake, along with that of many other emerging PFASs, continued to grow in three sampling campaigns from 2016 to 2021. Considering the environmental persistence and toxicity of structurally similar PFECAs (e.g., HFPO-DA), studies on C7 HFPO-TA are urgently needed.

Tetramethylammonium Fluoride: Fundamental Properties and Applications in C-F Bond-Forming Reactions and as a Base

Nucleophilic ionic sources of fluoride are essential reagents in the synthetic toolbox to access high added-value fluorinated building blocks unattainable by other means. In this review, we provide a concise description and rationale of the outstanding features of one of these reagents, tetramethylammonium fluoride (TMAF), as well as disclosing the different methods for its preparation, and how its physicochemical properties and solvation effects in different solvents are intimately associated with its reactivity. Furthermore, herein we also comprehensively describe its historic and recent utilization, up to December 2021, in C-F bond-forming reactions with special emphasis on nucleophilic aromatic substitution fluorinations with a potential sustainable application in industrial settings, as well as its use as a base capable of rendering unprecedented transformations.

Enantiospecific deoxyfluorination of cyclic α-OH-β-ketoesters

We herein report the deoxyfluorination of cyclic α-hydroxy-β-ketoesters using diethylaminosulfur trifluoride (DAST). The reaction proceeds with excellent levels of stereospecificity, giving the configurationally inverted α-fluoro-β-ketoesters in high yields under operationally simple conditions.