C F Bond Research Articles

An innovative and eco-friendly modality for synthesis of highly fluorinated graphene by an acidic ionic liquid: Making of an efficacious vehicle for anti-cancer drug delivery

Fluorination of graphene nanomaterials has multitude merits owing to the peculiar temperament of the carbon-fluorine (C-F) bond. However, the current synthesis modalities of fluorinated graphene (FG) are based on the usage of toxic materials at high temperatures, which are problematic to be used. The methods to overcome these problems are challenging for chemists. Ionic liquids (ILs) have been used in several chemical processes as auxiliaries and eco-friendly alternatives instead of volatile organic solvents because of their properties. Consequently, herein we exploited a highly effective and green process for the synthesis of FG at mild temperature (80 °C) by using ammonium fluoride salt as fluorine agent and a synthesized acidic IL ([TEA]+[TFA]–) as a solvent. Our goal was to synthesize enriched FG with a high degree of fluorination (66.4 wt.% of F) and F/C ratio (2.2), which measured and confirmed by XPS analysis. Subsequently, the obtained FG was used as a nanocarrier for delivery of curcumin to cancerous cells. The in-vitro results showed that these nanosheets possessed a higher Cur-loading efficiency (78.43%) than commercial FG (52.12%) due to the sheet-like structure with folded edges. This, in turn, translated into an excellent in-vitro anti-cancer effect when tested against cancerous cells.

Photoredox/Nickel Dual-Catalyzed Reductive Cross Coupling of Aryl Halides Using an Organic Reducing Agent.

A successful protocol for the reductive aryl-aryl cross-coupling of polyfluorinated arenes with a broad range of aryl halides has been developed. Sequential carbon-fluorine bond cleavage and carbon-carbon bond formation are two of the important features of the reaction. Addition of an aryl radical anion to a nickel intermediate was achieved for the first time using polyfluoroarenes as radical precursors. This, in combination with the excellent para selectivity, paves the way for the synthesis of various new multifluorinated biaryl compounds.

Be cautious applying carbon-fluorine bonds in drug delivery

As reported in Chemosphere by Colles et al. (2020), there are multiple pathways for human exposure to poly- and perfluoroalkyl substances (PFAS). Now, a new chemical formation of C–F bonds in drug delivery lead to concerns for human exposure as these inert chemical formations are resistance to metabolic degradation and excretion.

Teaching bismuth to make and break bonds

Organometallics One major reason why transition metals are good catalysts is that they can shuttle between oxidation states. This flexibility lets them slide in and out of chemical bonds; so, for instance, they can snip a bond between carbon and boron and then stitch a carbonfluorine bond in its place. Planas et al. now report that bismuth can also orchestrate such bond-swapping events. They implement a fully catalytic cycle for fluorination of aryl boronates, in which bismuth hops between its +3 and +5 oxidation states. Science , this issue p. [313][1] [1]: /lookup/doi/10.1126/science.aaz2258

Intramolecular aryl-aryl coupling via C-F bond activation tolerant towards C-I functionality.

Herein we report a transition-metal free activation of a particularly stable aromatic carbon-fluorine bond allowing intramolecular aryl-aryl coupling which is orthogonal to carbon-iodine functionality.

Carbon-fluorine bond cleavage mediated by metalloenzymes.

Fluorochemicals are a widely distributed class of compounds and have been utilized across a wide range of industries for decades. Given the environmental toxicity and adverse health threats of some fluorochemicals, the development of new methods for their decomposition is significant to public health. However, the carbon-fluorine (C-F) bond is among the most chemically robust bonds; consequently, the degradation of fluorinated hydrocarbons is exceptionally difficult. Here, metalloenzymes that catalyze the cleavage of this chemically challenging bond are reviewed. These enzymes include histidine-ligated heme-dependent dehaloperoxidase and tyrosine hydroxylase, thiolate-ligated heme-dependent cytochrome P450, and four nonheme oxygenases, namely, tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, 2-oxoglutarate-dependent hydroxylase, Rieske dioxygenase, and thiol dioxygenase. While much of the literature regarding the aforementioned enzymes highlights their ability to catalyze C-H bond activation and functionalization, in many cases, the C-F bond cleavage has been shown to occur on fluorinated substrates. A copper-dependent laccase-mediated system representing an unnatural radical defluorination approach is also described. Detailed discussions on the structure-function relationships and catalytic mechanisms provide insights into biocatalytic defluorination, which may inspire drug design considerations and environmental remediation of halogenated contaminants.

Fluorinative Rearrangement Involving Cleavage and Recombination of Carbon-Fluorine Bond: Synthesis of Functionalized Allylic gem-Difluorides from Propargylic Fluorides

Fluorinative Rearrangement Involving Cleavage and Recombination of Carbon-Fluorine Bond: Synthesis of Functionalized Allylic <i>gem</i>-Difluorides from Propargylic Fluorides

The direct trifluoromethylsilylation and cyanosilylation of aldehydes via an electrochemically induced intramolecular pathway.

The initiator-free electrochemical trifluoromethylsilylation and cyanosilylation of aldehydes were developed in an undivided cell. A DFT study reveals that the direct cathodic activation of trimethylsilyl reagents significantly released the congestion around the 'Si' atom, allowing the Si-O bond affinity to form concerted anion intermediates with aldehydes. Thus, intramolecular -CF3 and -CN migration make the reactions much easier to carry out without initiators.

Hydrophobic surface modification toward highly stable K2SiF6:Mn4+ phosphor for white light-emitting diodes

K2SiF6:Mn4+ phosphor is well known for its excellent red emission performance which is vital for improving the color rendering of white light-emitting diodes. However, the poor moisture resistance limits its application in optical devices. In this paper, K2SiF6:Mn4+ phosphor is coated with an inorganic hydrophobic protective layer to obtain good moisture resistance. Chemical vapor deposition method was used to decompose acetylene at high temperature, and the generated nanoscale carbon layer worked as a hydrophobic protective coating on the surface of the phosphor. Microstructure, compositions and properties of the synthesized K2SiF6:Mn4+@C phosphor were investigated in detail. It is found that most of the deposited carbon is coated on the surface of phosphor crystals in amorphous state. The carbon atoms are bonded with the fluorine element in K2SiF6:Mn4+ phosphor, forming carbon-fluorine (C–F) covalent bonds. The moisture resistance of K2SiF6:Mn4+@C phosphor is improved owing to the protection of the hydrophobic carbon. The relative emission intensity of K2SiF6:Mn4+@C phosphor could maintain 73% of the initial luminous intensity after immersing in the aqueous solution at room temperature for 8 h, whereas K2SiF6:Mn4+ phosphor without carbon coating was only 0.7% remaining of the initial value under the same conditions.

Pollutant-accelerated aging behaviors of fluorocarbon coating in tropical marine atmosphere

The aging behavior of polyvinylidene fluoride coatings in a tropical marine atmosphere was studied by natural exposure tests. The surface morphologies, chemical structures, and barrier effects of the coatings after natural weathering were investigated by scanning electron microscopy, attenuated total reflection Fourier transform infrared, X-ray photoelectron spectroscopy, and electrochemical impedance spectra measurements. Grey relational analysis was also performed to establish the relationship between environmental factors and degradation behaviors. It was found that the degradation of the coatings was accelerated, manifesting the breakage of CF bonds after 18 months of exposure at Hainan test site. With the aid of grey relational analysis, temperature, humidity, sunshine duration, and ammonia deposition were the most important factors that greatly affected the aging behaviors of the coatings. Therefore, a two-step degradation mechanism was proposed for the aging process. The first step was the degradation of the acrylic polyurethane resin through the photo-oxidation reactions. The second step was the dehydrogenation and defluorination of the fluorocarbon resin resulting from the ammonia-induced alkaline environment.

Preparation and characterization of PFTS grafted alumina supported zirconia (ASZ) membrane for removal of phenol from aqueous solution

Asymmetric alumina supported zirconia (ASZ) grafted 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFTS) membranes were successfully prepared. The structure, micromorphology, surface elements, roughness and hydrophobicity of the ASZ membrane before and after grafting were evaluated by XRD, SEM, EDS, AFM and contact angle, respectively. The effects of PFTS concentration, different solvents and alkali pretreatment on the hydrophobicity of the membrane surface were investigated systematically. The surface roughness and contact angle increased while the SFE decreased as the pH of the alkali pretreatment increased. The results show that the hydrophobicity of the PFTS grafted membrane depends on the roughness of the modified membrane surface and the low surface energy of the CF2 and CF3 bonds in the PFTS molecule on the membrane surface. The grafting mechanism of ASZ membrane with PFTS was studied by various analytical methods such as XPS, FTIR and TG-DSC, and the grafting process was verified. According to obtained results, PFTS chains were grafted onto the ASZ surface successfully. The PFTS grafted ASZ ceramic membrane is suitable for pervaporation to remove phenol from aqueous solutions, the phenol removal increased from 29.1 mg/L to 138.73 mg/L as the pH of the pretreatment increased from 7 to 11.

Electrochemical Oxidation of Hexafluoropropylene Oxide Dimer Acid (GenX): Mechanistic Insights and Efficient Treatment Train with Nanofiltration.

Hexafluoropropylene oxide dimer acid (HFPO-DA, trade name GenX) is a perfluoroalkyl ether carboxylic acid (PFECA) that has been detected in watersheds around the world. Similar to other per- and polyfluoroalkyl substances (PFASs), few processes are able to break HFPO-DA's persistent carbon-fluorine bonds. This study provides both experimental and computational lines of evidence for HFPO-DA mineralization during electrochemical oxidation at a boron-doped diamond anode with a low potential for the generation of stable organofluorine intermediates. Our density functional theory calculations consider the major operative mechanism, direct electron transfer, throughout the entire pathway. Initial oxidative attack does not break the ether bond, but leads to stepwise mineralization of the acidic side chain. Our mechanistic investigations reveal that hydroxyl radicals are unreactive toward HFPO-DA, while electrochemically activated sulfate facilitates its oxidation. Furthermore, we demonstrate that an NF90 membrane is capable of removing 99.5% of HFPO-DA from contaminated water. Electrochemical treatment of the nanofiltration rejectate is shown to reduce both energy and electrode costs by more than 1 order of magnitude compared to direct electrochemical treatment of the raw water. Overall, a nanofiltration-electrochemical oxidation treatment train is a sustainable destructive approach for the cost-effective elimination of HFPO-DA and other PFASs from contaminated water.

Experimental and theoretical analysis on decomposition and by-product formation process of (CF3)2CFCN mixture

Although sulfur hexafluoride (SF6) is widely used in gas-insulated electrical equipment due to the excellent electrical insulation and arc-interruption behaviors, its strong greenhouse effect with high glow warming potential (GWP) has been driving the research on environmentally friendly gases for SF6 alternatives. Recently, the heptafluoro-isobutyrontrile (CF3)2CFCN (3M NovecTM 4710) is reported to have the potential to replace SF6. The decomposition characteristic of gas insulating medium is one of the basic conditions to measure whether it has the feasibility of replacing SF6. However, the decomposition characteristic of (CF3)2CFCN and the formation mechanism of by-products are still unclear. In this paper, a series of AC corona discharge experiments were performed, and the gas by-products of (CF3)2CFCN mixed with CO2, N2 and air were qualitatively analyzed by gas chromatography mass spectrometry (GC/MS) method, respectively. Then, the decomposition mechanism of (CF3)2CFCN molecule and the formation mechanism of gas by-products were studied via density functional theory (DFT) method. The results show that the major gas by-products are CO, CO2, C2O3F6, CF4, C2F6, C3F6, C3F8, C2F4, (CF3)3CF, CF3CN, C2F5CN and CNCN, in addition to trace amounts of F3CC≡CCF3 and CF3CF=CFCF3. Among the three initial dissociation pathways of (CF3)2CFCN molecule, a C-CF3 bond fission pathway that produces CF3CFCN and CF3 radicals is identified as the thermodynamically favorable channel. The bond energy of C–CF3 bond calculated at M06-2X/def2-QZVP//M06-2X/6-311G(d,p) level is 94.7 kcal/mol.

Theoretical study of the internal rotational barriers of fluorine, chlorine, bromine, and iodine-substituted ethanes

Physical and chemical characteristics of flexible compounds are extremely dependent of internal rotation barriers. On the other hand, halides of organic compounds are extremely common, and the nature of their rotation barriers are still poorly understood. As a simple example, the experimental height of the internal rotational barrier decreases with the number of fluorine-substituted in ethane, C2H5F, C2H4F2, and C2H3F3. For chlorine-substituted ethane C2H5Cl, C2H4Cl2 and C2H3Cl3 the internal rotational barrier converges in an opposite manner. No experimental results are available for the bromine- and iodine-substituted compounds C2H5Br, C2H4Br2, C2H3Br3, C2H5I, C2H4I2, and C2H3I3. In light of lack of both an adequate explanation for this phenomenon and experimental results for Br and I, the present work studied these compounds using different levels of theory: MP2, MP3, MP4, QCISD(T) and CCSD(T) methods, and the G3 and G3CEP composite theories. The results showed that the G3 and G3CEP theories were the most accurate calculations for the F- and Cl-substituted compounds as a result of the additive contributions of the energy values. From Natural Bond Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) it was verified that the internal rotational barriers decrease with the addition of Fluorine atoms for fluorine-containing ethanes and can be explained by: π character in the CF bond and delocalization indexes (DI(A)) by QTAIM analysis; the interaction of the ligand and anti-ligand orbitals by NBO analysis and for the descriptors by EDA. On the other hand, the enlargement of the barriers with the addition of Cl, Br and I atoms for substituted ethanes, are dominated by the large electronic cloud of these halogens, which generates significant steric repulsion.

Effect of the Cove Region Geometry in Polycyclic Aromatic Hydrocarbons on Alumina‐Assisted Cyclodehydrofluorination

Despite conventional opinion on high inertness of aluminum oxide and exceptional stability of the carbon–fluorine bond, activated γ‐alumina effectively polarizes the C–F bond. This process is known to implement effective C–C coupling in the cove region, leading to intramolecular annulation and formation of non‐alternant polycyclic aromatic hydrocarbons (PAHs). Herein, the importance of the cove region geometry on annulation efficiency is shown. This is demonstrated using precursor 1 as a model, which allows investigation of the cove region's major feature, namely its helical geometry, and effect of its structure on the efficiency of intramolecular C–C bond formation. Herein, the synthesis of 1, its behavior on activated alumina, and reasoning for the observed outcomes are described.

Synthesis of Seven-membered Ring Containing Difluoromethylene Unit by Sc(OTf)3-catalyzed Activation of Single C–F Bond in CF3 Group

A Sc(OTf)3-catalyzed activation of a single C–F bond in a CF3 group is described. This reaction has two interesting features: (1) the synthesis of difluoromethylene compounds through Lewis acid-cat...

Degradation of Perfluorooctane Sulfonamide by Acinetobacter Sp. M and Its Extracellular Enzymes.

The Acinetobacter sp. strain M isolated from a contaminated soil sample in Jiangsu Province of China was found to be able to degrade perfluorooctane sulfonamide (PFOSA) effectively. Fluoride anion (F- ) released from PFOSA degradation was detected by ion chromatography, and showed positive correlation to the growth curve of Acinetobacter sp. strain M. The PFOSA degradation efficiency of strain M was approximately 27 %, as assessed by GC analysis. It was shown that enzymes localized outside of cells of Acinetobacter sp. strain M catalyzed the degradation of PFOSA. This further indicates a possibly new (multi-step/pathway) mechanism for PFOSA degradation. It revealed that the extracellular enzyme of the Acinetobacter strain M preferentially cleaves carbon-carbon and carbon-fluorine bonds instead of destroying the carbon-sulfur bond. The growth condition for Acinetobacter sp. strain M was optimized at 30 °C and pH 7.0 in the presence of 2000 mg L-1 of PFOSA and 0.5 % (v/v) of Tween-20. The optimal PFOSA degradation time was found to be 12 h, with a degradation efficiency of 76 % by extracellular enzymes in strain M as determined by GC analysis. The result may provide potential applications for biodegradition of perfluoro organic compounds, such as derivatives of perfluorooctane (C8).

Metal-Free Construction of the C(sp3)-CF3 Bond: Trifluoromethylation of Hydrazones with Togni's Reagent under Mild Conditions.

A metal-free trifluoromethylation of hydrazones with Togni's reagent under mild conditions was developed. Various functional groups including ester, methoxy, dimethoxy, nitro, halogen, and heterocyclic compounds were tolerated. This simple and green strategy provides a practical tool to construct C(sp3)-CF3 bonds.

Enantioselective construction of remote tertiary carbon-fluorine bonds.

The carbon-fluorine bond engenders distinctive physicochemical properties and significant changes to general reactivity. The development of catalytic, enantioselective methods to set stereocentres that contain a benzylic C-F bond is a rapidly evolving goal in synthetic chemistry. Although there have been notable advances that enable the construction of secondary stereocentres that contain both a C-F and a C-H bond on the same carbon, significantly fewer strategies are defined to access stereocentres that incorporate a tertiary C-F bond, especially those remote from pre-existing activating groups. Here we report a general method that establishes C-F tertiary benzylic stereocentres by forging a C-C bond via a Pd-catalysed enantioselective Heck reaction of acyclic alkenyl fluorides with arylboronic acids. This method provides a platform to rapidly incorporate significant functionality about the benzylic tertiary fluoride by virtue of the diversity of both reaction partners, as well as the ability to install the stereocentres remotely from pre-existing functional groups.

Visible-light mediated trifluoromethylation of p-quinone methides by 1,6-conjugate addition using pyrylium salt as organic photocatalyst

A transition metal free visible light mediated organo photoredox catalyzed trifluoromethylation of p-quinone methides (p-QMs) to construct fluoro-analogs of dichlorodiphenyltrichloroethane (DDT) is reported using a bench stable, inexpensive Langlois reagent as a trifluoromethyl radical source. This protocol could generate a benzylic C(sp3)-CF3 bond with excellent yield under mild reaction conditions using 1,6-conjugate addition/aromatization of trifluoromethyl radical in the absence of any external additives. Further, we demonstrate di-trifluoromethylation and gram scale synthesis of this reaction.