Presence Of Hydrogen Fluoride Research Articles

Deoxofluorination of graphite oxide with sulfur tetrafluoride.

In this study, deoxofluorination of graphite oxide (GO) using sulfur tetrafluoride (SF4) at a temperature below the decomposition temperature of GO (∼200 °C) was investigated for the first time with and without HF catalysis. At 25 °C, the reaction proceeds only at high SF4 pressures (≥8 atm) when not catalyzed by HF and at 1 atm SF4 under the catalysis of HF. The degree of fluorination increases at higher temperatures and SF4 pressures. Hydroxy and carbonyl groups are replaced by fluorine following this reaction, and SF4 and SOF2 are introduced into the product, while the epoxy groups do not react. SF4 and SOF2 in the products are removed by washing with water. The obtained product is less hygroscopic than pristine GO owing to the hydrophobicity of the fluorine atom. The interlayer separation of the product is increased after deoxofluorination despite the smaller size of fluorine than the sizes of the oxygen-containing functional groups. When compared with direct fluorination using elemental fluorine, deoxofluorination using SF4 has the advantages of high reactivity with hydroxy groups and the preservation of the carbon skeleton, and the reaction results in the formation of graphite oxyfluoride.

Stability of Hydrogen Fluoride Under Water-Gas-Reaction Conditions

The prime objective of the investigation was to prove the stability of hydrogen fluoride under water-gas-reaction conditions. Calculations of the thermodynamically equilibrium composition of substances in the system of elements C–H–F–O were conducted, and it has been shown that with excess carbon and at a temperature of 1000 to 2000 K, the basic components of the mixture are carbon mono- and dioxide, hydrogen, methane, and hydrogen fluoride, and carbon fluorides and oxyfluorides are absent. At a temperature above 1300 K, the thermodynamically equilibrium mixture consists of carbon monoxide, hydrogen, and hydrogen fluoride. Calculation results have been confirmed by laboratory experiments in which the only fluorine-containing substance, i.e., hydrogen fluoride, was found as part of the products of interaction of water and carbon in the presence of hydrogen fluoride at a temperature of the order of 1500 K. The obtained results can become a basis for the technology of obtaining anhydrous hydrogen fluoride from its aqueous solutions, including the azeotropic one, by high-temperature interaction of the steam and carbon at

Chemical composition and formation mechanisms in the cathode-electrolyte interface layer of lithium manganese oxide batteries from reactive force field (ReaxFF) based molecular dynamics

Lithium manganese oxide (LiMn2O4) is a principal cathode material for high power and high energy density electrochemical storage on account of its low cost, non-toxicity, and ease of preparation relative to other cathode materials. However, there are well-documented problems with capacity fade of lithium ion batteries containing LiMn2O4. Experimental observations indicate that the manganese content of the electrolyte increases as an electrochemical cell containing LiMn2O4 ages, suggesting that active material loss by dissolution of divalent manganese from the LiMn2O4 surface is the primary reason for reduced cell life in LiMn2O4 batteries. To improve the retention of manganese in the active material, it is key to understand the reactions that occur at the cathode surface. Although a thin layer of electrolyte decomposition products is known to form at the cathode surface, the speciation and reaction mechanisms of Mn2+ in this interface layer are not yet well understood. To bridge this knowledge gap, reactive force field (ReaxFF) based molecular dynamics was applied to investigate the reactions occurring at the LiMn2O4 cathode surface and the mechanisms that lead to manganese dissolution. The ReaxFFMD simulations reveal that the cathode-electrolyte interface layer is composed of oxidation products of electrolyte solvent molecules including aldehydes, esters, alcohols, polycarbonates, and organic radicals. The oxidation reaction pathways for the electrolyte solvent molecules involve the formation of surface hydroxyl species that react with exposed manganese atoms on the cathode surface. The presence of hydrogen fluoride (HF) induces formation of inorganic metal fluorides and surface hydroxyl species. Reaction products predicted by ReaxFF-based MD are in agreement with experimentally identified cathode-electrolyte interface compounds. An overall cathode-electrolyte interface reaction scheme is proposed based on the molecular simulation results.

Self-assembly of (NH4)0.3TiO1.1F2.1 crystal by dinitrogen fixation as a precursor of N-doped TiO2 nanosheets

Semiconductor TiO2 has been always extensively studied for maximizing its environmental- and energy-related applications with tailored facets or doped crystal structure, especially for photocatalysis, solar cell devices, sensors, catalyst supports, and supercapacitor. In this study, in air or argon atmosphere, a novel facile and effective method has been successfully exploited to prepare N-doped TiO2 nanosheets (air-TiO2 and Ar-TiO2) by annealing treatment of non-stoichiometric ammonium oxofluorotitanates crystal ((NH4)0.3TiO1.1F2.1) with layer-by-layer self-assembled morphology, which is obtained based on the dinitrogen fixation of TiCl4 in the presence of hydrogen fluoride under mild condition. In this method, the conversion of dinitrogen to ammonium salt has been demonstrated by means of isotopic labeling experiments with labeled 15N2 gas acting as benign oxidant and isopropanol as suitable reductant. The resultant of N-doped TiO2 nanosheets exhibits an enhancement of photocatalytic activity by degrading RhB under visible-light irradiation. In addition, the as-prepared Ar-TiO2 of N-doped TiO2 nanosheets obtained from Ar atmosphere also shows a higher electrochemical performance compared with reported pure TiO2 in the application of supercapacitor. In this study, in air or argon atmosphere, a novel facile and effective method has been successfully exploited to prepare N-doped TiO2 nanosheets (air-TiO2 and Ar-TiO2) by annealing treatment of non-stoichiometric ammonium oxofluorotitanates crystal ((NH4)0.3TiO1.1F2.1) with layer-by-layer self-assembled morphology, which is obtained based on the dinitrogen fixation of TiCl4 in the presence of hydrogen fluoride under mild condition.

Phase formation in the ZrO(NO3)2-NaF(HF)-H3PO4-H2O system at 20°C

Phase formation in the ZrO(NO3)2-NaF(HF)-H3PO4-H2O system was studied at 20°C and 2.0–14.5 wt % ZrO2 in the initial solution along sections with molar ratios PO43−/Zr = 0.5 and 1.5 and also in the presence of hydrogen fluoride at Na/Zr = 1 and PO43−/Zr = 0.5, 1.0, and 1.5. Crystalline zirconium hydrophosphate Zr(HPO4)2 · H2O, fluorozirconates Na5Zr2F13 and Na7Zr6F31 · 12H2O, fluorophosphatozirconates NaH2Zr3F3(PO4)4 · 3H2O and NaZr2F6(PO4) · 4H2O, and amorphous NaZrO0.5F(PO4) · 4H2O (provisional composition) were separated at room temperature. NaH2Zr3F3(PO4)4 · 3H2O and NaZr2F6(PO4) · 4H2O were prepared for the first time and were studied by crystal-optical, elemental, and thermal analyses, X-ray powder diffraction, IR spectroscopy, scanning electron microscopy (SEM), and X-ray microanalysis. Na7Hf6F31 · 12H2O was found to exist in a mixture with the hydrophosphate.

Effect of co-sensitization of CdSe nanoparticles with N3 dye on TiO2 nanotubes

Cadmium selenide (CdSe) nanoparticles were synthesized in aqueous medium using mercaptopropionic acid (MPA) as the stabilizer at the temperature 100°C. Air stable sodium selenite (Na2SeO3) was used as the selenium source. The synthesized particles were used to co-sensitize the TiO2 nanotubes with N3 dye. Ex-situ linker assisted method was used to sensitize the nanotubes by CdSe nanoparticles. Electrochemical anodization technique was employed to prepare TiO2 nanotubes in the presence of hydrogen fluoride (HF) as electrolyte. A solar cell was fabricated using co-sensitized TiO2 nanotubes by N3 dye/CdSe nanoparticles as the anode and platinum coated fluorine doped tin oxide (FTO) electrode as the cathode. Polysulphide (S2-/Sx2-) mixture was used as the electrolyte. UV–Visible, SEM, AFM and TEM analysis were used to characterize the synthesized particles and TiO2 nanotubes.

Opening of the four-membered ring in perfluorinated 1-alkyl-2-phenyl- and 1-aryl-1,2-dihydrocyclobutabenzenes in the system I2-SbF5

Reactions of perfluorinated 1-phenyl-, 1-(2-ethylphenyl)-, 1-(4-ethylphenyl)-, 1-methyl-2-phenyl-, and 1-ethyl-2-phenyl-1,2-dihydrocyclobutabenzenes with iodine in antimony pentafluoride at 130°C, followed by hydroysis of the reaction mixture, resulted in the formation of perfluorinated 2-methyl-, 2-ethyl-2′-methyl-, 4-ethyl-2′-methyl-, 2-ethyl-, and 2-propylbenzophenones via opening of the four-membered ring in the initial cyclobutabenzene at the C1–C2 bond. The presence of hydrogen fluoride facilitates the process and promotes profound transformations leading to anthracene derivatives.

Hydrogenation of Simple Aromatic Molecules: A Computational Study of the Mechanism

Quantum chemistry calculations have been used to study the metal-free hydrogenation reactions of a variety of simple aromatic, heteroaromatic, and related linear conjugated systems. We find that the barrier for uncatalyzed 1,4-hydrogenation is always substantially lower (by approximately 200 kJ mol-1) than that for 1,2-hydrogenation, despite similar reaction enthalpies. The presence of hydrogen fluoride as a catalyst is found to decrease the 1,2-hydrogenation barriers but, in most cases, to slightly increase the 1,4-hydrogenation barriers when a constrained geometric arrangement is employed. These qualitative observations are consistent with orbital symmetry considerations, which show that both the uncatalyzed 1,4-hydrogenation and the catalyzed 1,2-hydrogenation are formally symmetry-allowed processes. An extreme example of the catalyzed 1,2-hydrogenation of benzene is provided by the involvement of a second molecule of hydrogen, which leads to a substantial lowering of the barrier. The effect of catalysis was further investigated by applying a selection of additional catalysts to the 1,2- and 1,4-hydrogenation of benzene. A decreasing barrier with increasing catalyst acidity is generally observed for the catalytic 1,2-hydrogenation, but the situation is more complex for catalytic 1,4-hydrogenation. For the uncatalyzed 1,4-hydrogenation of aromatic systems containing one or more nitrogen heteroatoms, the barriers for [C,C], [C,N], and [N,N] hydrogenations are individually related to the reaction enthalpies by the Bell-Evans-Polanyi principle. In addition, for a given reaction enthalpy, the barriers for [C,C] hydrogenation are generally lower than those for [C,N] or [N,N] hydrogenation. Finally, we find that the distortion experienced by the reactants in forming the transition structure represents a secondary factor that influences the reaction barrier. The correlation between these quantities allows the 1,4-hydrogenation barriers to be predicted from a ground-state property.

Synthesis of titanium silicalite-2 (TS-2) from methylamine-tetrabutylammonium hydroxide media

Titanium silicalites have been synthesized by new procedures using hydrogen fluoride-methylamine media. X-ray diffraction has revealed that the products were identical to TS-2 with the MEL structure. Titanium ions were incorporated into the zeolite framework, as confirmed by X-ray powder diffraction (XRD, unit cell expansion), infrared (IR) and ultraviolet–visible (UV–Vis) spectroscopies. The presence of hydrogen fluoride as a co-mineralizer in the gel can improve the crystallization. Increasing the amount of methylamine in the gel is led to a remarkable incorporation of titanium in the MEL framework. The advantage of these methods is the use of cheaper sources (Ti and Si) than those used in a conventional method; but the amount of titanium incorporated into the TS-2 lattice via the new methods is different. For different titanium containing TS-2 samples catalytic conversions, selectivities and yields in the hydroxylation of benzene with hydrogen peroxide were different.

Synthesis of titanium silicalite-2 (TS-2) from methylamine-tetrabutylammonium hydroxide media

Titanium silicalites have been synthesized by new procedures using hydrogen fluoride-methylamine media. X-ray diffraction has revealed that the products were identical to TS-2 with the MEL structure. Titanium ions were incorporated into the zeolite framework, as confirmed by X-ray powder diffraction (XRD, unit cell expansion), infrared (IR) and ultraviolet–visible (UV–Vis) spectroscopies. The presence of hydrogen fluoride as a co-mineralizer in the gel can improve the crystallization. Increasing the amount of methylamine in the gel is led to a remarkable incorporation of titanium in the MEL framework. The advantage of these methods is the use of cheaper sources (Ti and Si) than those used in a conventional method; but the amount of titanium incorporated into the TS-2 lattice via the new methods is different. For different titanium containing TS-2 samples catalytic conversions, selectivities and yields in the hydroxylation of benzene with hydrogen peroxide were different.

Improvement in the mechanical properties of polyacrylonitrile (PAN)-based carbon fibers after fluorination

Intercalation of fluorine in polyacrylonitrile (PAN)-based carbon fibers (HTT∼1400°C) was carried out in the presence of hydrogen fluoride as an additive. The study revealed that there is no definite stage formation in the fluorinated compounds, rather fluorine is trapped in the defects or diffused in to graphene layers and form covalent C–F bond at the surface of the fibers. Mechanical properties improve for lower concentrations of fluorine into the fibers (up F/C∼0.04%).

The Crystal Structures of Peroxonium Hexafluoroantimonate H3 O2 SbF6 and Bis(dihydrogenperoxo)hydrogen Hexafluoroantimonate H5 O4 SbF6.

Protonated hydrogen peroxide is produced from the reaction of antimony pentafluoride with bis(trimethylsilyl)peroxide in the presence of hydrogen fluoride. Depending on the stoichiometry of the reaction mixture, the compounds H3 O2 SbF6 and H5 O4 SbF6 are formed, which are stable up to room temperature and have been characterized by X-ray crystallography. The structure of the H3 O2+ ion is shown on the right.

Preparation of 2,3,3,3-tetrafluoropropene from trifluoroacetylacetone and sulphur tetrafluoride

Practical details are presented for the laboratory preparation of 2,3,3,3-tetrafluoropropene in good yield from trifluoroacetylacetone and sulphur tetrafluoride in the presence of hydrogen fluoride. The gas-phase IR spectrum of the tetrafluoropropene (b.p., −28 °C) is reproduced and a detailed analysis of the olefin's nuclear magnetic resonance (NMR) spectra ( 1H, 13C, 19F) is provided.

The Effect of Fluorine Additions to the Oxidation of Silicon

Experiments were carried out to study the effects of fluorine additions to a dry oxidation ambient. Two distinct classes of fluorine sources, liquid dichlorofluoroethane , and gaseous nitrogen trifluoride , were investigated. We experimentally found that small fluorine additions (up to 0.11% by volume) caused large enhancements in oxidation kinetics. The oxidation kinetics data were analyzed by both the power of time and linear‐parabolic models as a function of fluorine addition, temperature, and the type of fluorine additive. Thermodynamic calculations for these classes of fluorine sources were extensively carried out to determine the active oxidizing species that cause the significant enhancement of the oxidation. According to these calculations, the enhancement of oxidation could be explained by the presence of hydrogen fluoride (HF) and atomic fluorine (F). Secondary ion mass spectrometry (SIMS) was performed to study the incorporation behavior of fluorine into the oxide layer. oxides displayed peaks at the silicon‐oxide interface, while oxides exhibited flat fluorine profiles.

ChemInform Abstract: FLUORINATION WITH XENON DIFLUORIDE, REACTIONS WITH 1,1‐DIPHENYLETHYLENES

AbstractDie 1,1‐Diphenyläthylene (I) reagieren in Methylenchlorid mifXenondifluorid (II) bei Raumtemperatur in Gegenwart von Fluorwasserstoff oder Trifluoressigsäure in 65‐95%iger Ausbeute zu den Difluordiphenyläthanen (III).

Nitroxide chemistry. Part VII. Synthesis and some reactions of perfluoro-2,5-diazahexane 2,5-dioxyl

Oxidation by potassium permanganate of aqueous perfluoro-2,5-diazahexane-2,5-diol obtained by hydrolysis of a trifluoronitrosomethane–tetrafluoroethylene–phosphorus trichloride 2 : 1 : 1 adduct yields perfluoro-2,5-diazahexane 2,5-dioxyl. The dioxyl reacts with hydrogen bromide to give the parent diol, with nitric oxide to yield perfluoro-2,5-dinitro-2,5-diazahexane, with tetrafluoroethylene to provide perfluoro-(2,5-dimethyl-1,6-dioxa-2,5-diazacyclo-octane) and an alternating copolymer, –[O·N(CF3)·CF2CF2·N(CF3)·O·CF2CF2]–n, with perfluoropropene to afford perfluoro-(2,5,7-trimethyl-1,6-dioxa-2,5-diazacyclo-octane) and a copolymer, and with trifluoronitrosomethane or perfluoro-1-nitrosopropane to yield perfluoro-(2,5-dimethyl-1-oxa-2,5-diazacyclopentane). The last product rapidly oxidises iodide ion to iodine and decomposes slowly at room temperature into perfluoro-(N-methylenemethylamine) and perfluoropoly-[(N-methylenemethylamine)N-oxide); decomposition in the presence of hydrogen fluoride gives bistrifluoromethylamine and NN-bistrifluoromethylhydroxylamine. Flow pyrolysis of the diazacyclopentane at 155 °C and ca. 1 mmHg pressure yields a complex mixture believed to contain perfluoro-(N-methylenemethylamine)N-oxide.A laboratory apparatus for the continuous production of trifluoronitrosomethane via pyrolysis of trifluoroacetyl nitrite is described.

Fluorination with xenon difluoride. Reactions with 1,1-diphenylethylenes

Xenon difluoride reacts with 1,1-diphenylethylenes in the presence of hydrogen fluoride or trifluoroacetic acid as catalyst to form the corresponding 1,2-difluoroacetic acid as catalyst to form the corresponding 1,2-difluoro-1,1-diphenylethanes in nearly quantitative yields.

Kinetics of alkylation of phenol with propylene in the presence of hydrogen fluoride

Kinetics of alkylation of phenol with propylene in the presence of hydrogen fluoride

Alkylation of chlorobenzene with isobutylene in the presence of hydrogen fluoride

Alkylation of chlorobenzene with isobutylene in the presence of hydrogen fluoride

Solvent effects in the alkylation of benzene with 1-dodecene and trans-6-dodecene in the presence of hydrogen fluoride

Solvent effects in the alkylation of benzene with 1-dodecene and trans-6-dodecene in the presence of hydrogen fluoride