Journal of Fluorine Chemistry最新文献

Described herein is the direct amidation of a range of carboxylic acids, in moderate to excellent yields, using potassium hexafluorotitanate (K₂TiF₆) as a catalytic activator. The ready commercial availability, low cost, and ease of handling of the catalyst, as well as the simple, chromatography-free work-up of the reaction renders the process very appealing.

A new strategy for the synthesis of peptides incorporating racemic hexafluorovaline (hfVal) is presented. The synthetic pathway relies on the anti-Michael addition of benzyl amine derivatives to ad hoc prepared β-bis-trifluoromethyl-acryloyl-α-amino esters which proceeds in mild condition, high yields, even if with low stereocontrol. The following elaboration of the intermediates, namely deprotection of the benzyl moiety and coupling with α-amino esters allowed us to synthetize the targeted tripeptides in four overall synthetic steps, resulting in a synthetic pathway more favorable respect to those appeared in literature based on the synthesis and isolation of racemic Boc-hfVal-OH (eight synthetic steps).

The detection of organic pollutants in the environment is crucial due to their significant impact on human health. Formyl fluoride (HFCO) and carbonyl fluoride (COF₂) are toxic gasses that contribute to stratospheric ozone depletion. To explore a potential sensor material for these compounds, the adsorption properties of HFCO and COF₂ on pristine (8, 0) single-walled carbon nanotubes (SWCNTs), aluminum-doped SWCNTs (Al-SWCNTs), nitrogen-doped SWCNTs (N-SWCNTs), and aluminum nitride nanotube (AlNNTs) were investigated using density functional theory (DFT) calculations. Obtained structural and electronic results reveal no significant after HFCO and COF₂ adsorption on pristine SWCNT. However, the conductivity and polarizability of Al- SWCNT increases throw HFCO and COF₂ adsorption. It was shown that this adsorption strongly depends on molecular orientation toward SWCNT. Structural and electronic findings show that studied molecules undergoes a physical adsorption to N- SWCNT. However, AlNNT was also found to show significant changes in structural and electronic properties after HFCO and COF₂ adsorption. This adsorption leads to a significant (nearly 45%) reduction in the HOMO-LUMO gap of AlNNTs. Therefore, it is proposed from this study that Al-SWCNTs and AlNNTs are promising candidates for HFCO and COF₂ gas sensors. Moreover, AlNNTs exhibit intrinsic detection capabilities without structural manipulation via doping which makes AlNNTs particularly attractive for sensor applications. Moreover, the capability of AlNNT without manipulating makes this nanotube a good and easy made candidate for these compounds adsorption.

Analysis of the physicochemical parameters of saturated (hetero)cyclic carboxylic acids and their α-fluorinated analogues is described. Measured pK_a values revealed a significant influence of the single fluorine substituent on the compound's acidity (pK_a decreased by 1.3–2.4 units). This effect did not demonstrate additivity with electronic effects of other heteroatom (i.e., cyclic ether moiety). On the contrary, lipophilicity (LogP) of the corresponding anilides was almost unaffected upon α-substitution with a fluorine atom and mainly governed by the nature of the (hetera)cycloalkyl substituent. The obtained results suggest that polarization of the C–F bonds themselves does not define the fluorine effect on the compound's lipophilicity.

The organofluorine chemistry field has steadily increased over the years. In particular, the difunctionalization of unsaturated compounds is an efficient pathway toward the formation of regioselective and highly functionalized aliphatic compounds. This review depicts the recent advances made for simultaneously forming C−FG¹ and C−CF₂FG² on alkenes (FG = functional group) by catalysis. This review highlights approaches involving transition metal-catalyzed transformations and one electron manifold.

Air ingress accident scenarios may result in the oxidation of graphite matrix materials and cause serious safety problems in molten salt reactor. However, the oxidation behavior of the molten-salt-infiltrated graphite remains elusive. In this study, the effect of alkali fluoride salts (LiF, NaF, KF and ternary salt FLiNaK) on the oxidation behavior of graphite powder under air atmosphere was investigated. Thermogravimetric analysis and oxidation tests manifest that the initial oxidation temperature of the graphite is reduced from 720 °C to 510–610 °C, because of the presence of the alkali fluoride salts. The catalytic oxidation effect follows the order of KF > NaF > LiF. Careful characterizations reveal that the pristine graphite is mainly oxidized at the graphite edges, while salt-infiltrated graphite is mainly damaged at the graphitic basal planes. Density functional theory calculations suggest that the doping of alkali metal atoms does not change the physical adsorption feature of the oxygen molecule on the graphite plane surface, but increases its adsorption energy to facilitate the graphite oxidation reactions.

Nafion™ utilizes -SO₃H groups for proton conduction. Using an alternative proton-exchange functionality like -PO₃H₂, -COOH, etc., to replace -SO₃H in ion conductive fluoropolymers has attracted significant attention. For example, composite membranes comprising Nafion™ and perfluoro(carboxylic acid) bearing a -COOH group on its side chains have been used in color-alkali cells to reduce unwanted electrolyte crossovers. In the present paper, we reported a new synthetic strategy for constructing novel -PO₃H₂-bearing fluoropolymers (FBP). Our method employs a ZnI₂-promoted phosphorylation reaction of triethyl phosphite that converts benzyl alcohol on a side chain of a fluoropolymer into a benzylphosphodiester group, followed by trimethylsilyl chloride (TMSCl) hydrolysis to yield FBP. This strategy has enabled us to graft a fluoropolymer side chain directly with phosphonic acid. Although the in-plane proton conductivities of FBP fluoropolymers are lower than those of Nafion™ 115, most FBPs, especially Homo-FBP that has no fluoroalkyl ether group on its side chains, are significantly more stable against hydroxyl radical degradations in Fenton tests. This paper presents a new method for the synthesis of -PO₃H₂-containing fluoropolymers and our work also confirms a novel strategy for enhancing the long-term stability of a proton-conductive fluoropolymer in electrical devices—eliminating or reducing fluoroalkyl ether groups on the side chains of the polymer.

A series of asymmetrically fluorinated 2,2′-bibenzimidazoles were obtained by reaction of benzimidazole-2-carboxylic acid with fluorinated 1,2-phenylenediamines in polyphosphoric acid at elevated temperature. The tautomers of fluorinated 2,2′-bibenzimidazoles with a predominance of isomers containing F atoms in distant position relative to the NH group of the benzimidazole fragment are detected in DMSO‑d6 using NMR spectroscopy. The ratio of tautomers depends on the number and arrangement of F atoms in the initial fluorinated 1,2-phenylenediamines. Under similar conditions fluorinated 1,2-phenylenediamines in the presence of benzimidazole-2-carboxylic acid, but without its participation as well as without it, give fluorinated phenazine-2,3-diamines. The direction of transformation of fluorinated 1,2-phenylenediamines depends on the number and position of F atoms. Under similar conditions phenazine-2,3-diamine is not formed from non-fluorinated 1,2-phenylenediamine, but it is obtained with the presence of fluorinated 1,2-phenylenediamines. When fluorinated 1,2-phenylenediamines contain F atoms simultaneously at the positions 4 and 5, the hydrodefluorination of initial fluorinated 1,2-phenylenediamines occurs, resulting in less fluorinated 2,2′-bibenzimidazoles and phenazine-2,3-diamines. Hydrodefluorination of fluorinated 1,2-phenylenediamines in a polyphosphoric acid at elevated temperatures is the first example of the hydrodefluorination of fluorinated aromatic compounds containing strong donor substituents, such as amino groups. Polyphosphoric acid is shown to be a suitable medium for redox processes.

R1234ye(E) is an environmentally friendly working fluid that can be applied in refrigeration, heat pumps, and organic Rankine cycle systems, but it has issues with oxidative decomposition and flammability. Therefore, based on density functional theory, the oxidative decomposition mechanism of R1234ye(E) has been studied. The results indicate that the oxidative decomposition of R1234ye(E) is a typical chain reaction. The first stage is a chain-initiation reaction, where R1234ye(E) generates a large number of free radicals through initial self thermal decomposition reactions and collision reactions with oxygen. The most likely to occur is path 1–2, which is a homolytic reaction with an energy barrier of only 347.91 kJ/mol. The second stage is the chain-propagation reaction, including the reactions between R1234ye(E) and different free radical and subsequent reactions. The most likely to occur is path 5–1, which is a hydrogen abstraction reaction with an energy barrier of only 21.83 kJ/mol. The last stage is the chain-termination reaction, where the intermediates or products of the above reactions continue to react with the active free radicals until they are consumed. When all the reactants and free radicals are consumed and stable products are generated, the oxidative decomposition reaction ends. The research results provide a reference for the safe application of R1234ye(E) and other HFOs working fluids.

Synthesis of 2,2,3,3-tetraftluoro-γ-aminobutyric acid (tetraF-GABA) starting from commercially available 2,2,3,3-tetrafluorobutane-1,4-diol is described. The straightforward nine-step reaction sequence allowed the production of up to 20 g of the target amino acid in 41 % overall yield. Potentiometric titration revealed increased acidity of both ionizable moieties in the title compound (the pK_a values were diminished by 1.6 and 4.0 units for the COOH and NH₃⁺ groups, respectively, as compared to parent GABA). X-ray diffraction studies and DFT calculations demonstrated different preferential conformations in solid state and solution, although the fluorine gauche effect was observed in both cases.