First principles simulation of a superionic phase of hydrogen fluoride (HF) at high pressures and temperatures

We have conducted ab initio molecular dynamics simulations of hydrogen fluoride (HF) at pressures of 5-66 GPa along the 900 K isotherm. We predict a superionic phase at 33 GPa, where the fluorine atoms are fixed in a bcc lattice while the hydrogen atoms diffuse rapidly with a diffusion constant between 2 x 10(-5) and 5 x 10(-5)cm(2)s. We find that a transformation from asymmetric to symmetric hydrogen bonding occurs in HF at 66 GPa and 900 K. With superionic HF we have discovered a model system where symmetric hydrogen bonding occurs at experimentally achievable conditions. Given previous results on superionic H(2)O [Goldman et al., Phys. Rev. Lett. 94, 217801 (2005)] and NH(3) [Cavazzoni et al., Science 283, 44 (1999)], we conclude that high P, T superionic phases of electronegative element hydrides could be common.     

An equation of state for hydrogen fluoride

Using a similar approach as Lencka and Anderko [AIChE J. 39 (1993) 533], we developed an equation of state for hydrogen fluoride (HF), which can correlate the vapor pressure, the saturated liquid and vapor densities of it from the triple point to critical point with good accuracy. We used an equilibrium model to account for hydrogen bonding that assumes the formation of dimer, hexamer, and octamer species as suggested by Schotte [Ind. Eng. Chem. Process Des. Dev. 19 (1980) 432]. The physical and chemical parameters are obtained directly from the regression of pure component properties by applying the critical constraints to the equation of state for hydrogen fluoride. This equation of state together with the Wong–Sandler mixing rule as well as the van der Waals one-fluid mixing rule are used to correlate the phase equilibria of binary hydrogen fluoride mixtures with HCl, HCFC-124, HFC-134a, HFC-152a, HCFC-22, and HFC-32. For these systems, new equation of state with the Wong–Sandler mixing rule gives good results.     

Effect of evolved hydrogen fluoride on radiation-induced crosslinking and dehydrofluorination of poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVdF) was irradiated by ⁶⁰Co γ-rays with and without potassium hydroxide (KOH) under vacum. KOH tablets were added to absorb completely hydrogen fluoride (HF) which is the main volatile product of radiolysis of PVdF in the irradiation cell. In the presence of HF, the rates of radiation-induced crosslinking and dehydrofluorination of PVdF were lower than those in the absence of HF. The experimental results are discussed from the standpoint of stabilization of alkyl free radicals in PVdF by reaction with hydrogen fluoride.     

Effect of the range of interactions on the properties of fluids. 2. Structure and phase behavior of acetonitrile, hydrogen fluoride, and formic acid

To complete the study on the effect of the long-range part of Coulombic interactions on properties of complex polar and associating fluids, we have investigated in detail three compounds with extreme features: acetonitrile for its unusually large dipole moment, hydrogen fluoride with very strong hydrogen bonding, and formic acid for its potential formation of different n-mers in liquid and gaseous phases. The effect of the long-range Coulombic interactions on both the structure and thermodynamics of the homogeneous phase, and on the vapor-liquid equilibria has been examined using the same decomposition of realistic potential models into a short-range part and a residual part as in the previous paper [Kettler, M.; et al. J. Phys. Chem. B 2002, 106, 7537-7546]. The present results fully confirm the previous findings that the properties of polar and associating systems are determined primarily by the short-range interactions regardless of their nature, i.e., contributions arising from the long-range interactions constitute only a small portion of the total properties, and thus that the short-range potential counterpart of full realistic models can be used as a convenient reference for a successful perturbation expansion.     

Double-cavity calix[4]pyrrole derivative with enhanced capacity for the fluoride anion

A double-cavity calix[4]pyrrole derivative, meso-tetramethyl-tetra[N-(2-phenoxyethyl)-N'-phenylurea]calix[4]pyrrole, 1, with enhanced hosting ability for the fluoride anion has been designed and characterized. Its interaction with anions (fluoride, chloride, bromide, iodide, dihydrogen phosphate, hydrogen sulfate, perchlorate, nitrate, and trifluoromethane sulfonate) was qualitatively and quantitatively assessed through 1H NMR, conductance, and calorimetric studies. The outcome of these investigations demonstrates that 1 interacts only with fluoride and dihydrogen phosphate anions in dipolar aprotic media. However, the composition of these complexes differs in that two units of fluoride are taken per unit of 1, while a 1:1 anion/ligand complex is formed with the dihydrogen phosphate anion. Results from the 1H NMR studies are striking in that these not only provide information about the active sites of the ligand-anion interaction but also allow the establishment of the sequence of events taking place during fluoride complexation. Thus, hydrogen-bond formation between the pyrrolic hydrogen and the fluoride anion is followed by the uptake of a second anion through the same type of interaction, but with the phenyl urea. It is also the latter group that is responsible for the interaction of 1 with the dihydrogen phosphate anion. Finally, this paper illustrates the importance of structural information for the interpretation of the thermodynamics associated with these systems.     

Chemistry of organo halogenic molecules,LXXV. Polymer-supported hydrogen fluoride

Polymer-supported hydrogen fluoride prepared by reaction of hydrogen fluoride with crosslinked poly(styrene-$\text{co}$-4-vinyl- pyridine) containing 40–45 mol % of 4-vinylpyridine did not react with $\text{trans}$-stilbene, 1,2-diphenylacetylene, and cyclohexanol under various conditions, whereas 1-phenyl-1-hydroxy- 4-tert-butylcyclohexane was converted to 1-phenyl-4-tert-butylcyclohexene. Bromofluorination of various phenyl-substituted olefins with N-bromosuccinimide in the presence of polymer supported hydrogen fluoride in methylene chloride proceeds with Markovnikov type regioselectivity. Fluorination and halofluorination of norbornene with xenon difluoride or N-bromosuccinimide or N-chlorosuccinimide in the presence of polymer- supported hydrogen fluoride resulted in up to five products, with a large increase in halonortricyclane formation, compared to reactions in the presence of hydrogen fluoride-pyridine. Polymer-supported hydrogen fluoride, in comparison to hydrogen fluoride-pyridine, enhanced the $\text{endo}$ attack of the electrophile on norbornadiene by fluorination or halofluorination.     

Determination of fluoride with thorium nitrate by catalytic titration

Amperometry, constant-current potentiometry and spectrophotometry were used to follow the course of catalytic titrations of fluoride and silicofluoride with thorium nitrate. The hydrogen peroxide-iodide system was used as the indicator reaction. Titrations were performed in 50% ethanolic acetate buffer, pH 3.6. Amounts of 3.70-6.85 mg of ammonium fluoride, 5.53-10.79 mg of potassium fluoride and 4.34-8.41 mg of sodium silicofluoride were determined with a maximum average deviation of 0.9%. The results obtained are in good agreement with those of comparable methods.     

Many‐body energy decomposition analysis of cooperativity in hydrogen fluoride clusters

This article studies the cooperativity present in hydrogen fluoride clusters, (FH)_n, by means of a many‐body decomposition of the binding energy. With the aim of quantifying how the results depend on the calculation level, the partition was performed from dimer to hexamer at the RHF, MP2, and density functional (B3LYP) levels, and for the heptamer and octamer at the RHF and B3LYP levels, using a 6‐31++G(d, p) basis set in all cases. We obtain that, for a proper representation of the cooperative effects in hydrogen fluoride, at least the inclusion of the three‐body terms is fundamental. The contributions are found to be underestimated at the RHF level and overestimated at the B3LYP level, with respect to the MP2 results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Hydrogen fluoride analyzer for gases and aerosols

Many fire suppression agents are currently used, and the replacement candidates for these agents contain fluorine atoms. When these agents are used to extinguish a fire, large quantities of hydrogen fluoride gas can be produced from the thermal degradation of fluorinated organic compounds. A real-time analyzer has been developed to measure exposure levels of hydrogen fluoride gas and aerosols during fire suppression tests. A vacuum pump pulls air through a continuous denuder, where the toxic gas and aerosols are extracted from the air into an aqueous trapping solution. The trapping solution then passes through a flow cell, where a fluoride ion-selective electrode measures the fluoride ion concentration. A solenoid pump moves the trapping solution and calibration standards through the analyzer. Once calibrated, the analyzer can generate a concentration profile of hydrogen fluoride versus time. This hydrogen fluoride analyzer is portable and can be calibrated in about 5 min. It provides rapid response to hydrogen fluoride gas and aerosols, over a detection range from 1 to 5000 mg/m³.     

Density functional theory calculations of hydrogen-bond-mediated NMR J coupling in the solid state

A recently developed method for calculating NMR J coupling in solid-state systems is applied to calculate hydrogen-bond-mediated (2h) J NN couplings across intra- or intermolecular N-H...N hydrogen bonds in two 6-aminofulvene-1-aldimine derivatives and the ribbon structure formed by a deoxyguanosine derivative. Excellent quantitative agreement is observed between the calculated solid-state J couplings and those previously determined experimentally in two recent spin-echo magic-angle-spinning NMR studies ( Brown, S. P. ; et al. Chem. Commun. 2002, 1852-1853 and Pham, T. N. ; et al. Phys. Chem. Chem. Phys. 2007, 9, 3416-3423 ). For the 6-aminofulvene-1-aldimines, the differences in (2h) J NN couplings in pyrrole and triazole derivatives are reproduced, while for the guanosine ribbons, an increase in (2h) J NN is correlated with a decrease in the N-H...N hydrogen-bond distance. J couplings are additionally calculated for isolated molecules of the 6-aminofulevene-1-aldimines extracted from the crystal with and without further geometry optimization. Importantly, it is shown that experimentally observed differences between J couplings determined by solution- and solid-state NMR are not solely due to differences in geometry; long-range electrostatic effects of the crystal lattice are shown to be significant also. J couplings that are yet to be experimentally measured are calculated. Notably, (2h) J NO couplings across N-H...O hydrogen bonds are found to be of a similar magnitude to (2h) J NN couplings, suggesting that their utilization and quantitative determination should be experimentally feasible.     

Electron and hydrogen transfer in small hydrogen fluoride anion clusters

A new stable structure has been found for the anion clusters of hydrogen fluoride. The ab initio method was used to optimize the structures of the (HF)(3)(-), (HF)(4)(-), (HF)(5)(-), and (HF)(6)(-) anion clusters with an excess "solvated" electron. Instead of the well-known "zig-zag" (HF)(n)(-) structure, a new form, (HF)(n-1)F(-)···H, was found with lower energy. In this new form, the terminal hydrogen atom in the (HF)(n)(-) chain is separated from the other part of the cluster and the inner hydrogens transfer along the hydrogen bonds toward the outside fluoride. The negative charge also transfers from the terminal HF molecule of the chain to the center fluoride atoms. The (HF)(n)(-) clusters for n = 4, 5, and 6 have not yet been observed experimentally. These results should assist in the search for these systems and also provide a possible way to study the proton and electron transfer in some large hydrogen bonding systems.     

Stable dialkyl ether/poly(hydrogen fluoride) complexes: dimethyl ether/poly(hydrogen fluoride), a new,convenient, and effective fluorinating agent

The preparation, (1)H, (13)C, and (19)F NMR structural characterization as well as with DFT-based theoretical calculations of stable dialkyl ether/poly(hydrogen fluoride) complexes are reported. Dimethyl ether/poly(hydrogen fluoride) (DMEPHF), are stable complexes of particular interest and use. The DFT calculations, that are in agreement with NMR data, suggest a cyclic poly(hydrogen fluoride) bridged structure for DMEPHF. The complex, DME-5 HF was found to be a convenient and effective new fluorinating agent with the ease of workup and applied to several fluorination reactions, such as the hydrofluorination and bromofluorination of alkenes, and fluorination of alcohols giving good to excellent yield with high selectivity. Homologous dialkyl ether/poly(hydrogen fluoride) (R(2)O/[HF](n,), R = Et, nPr) systems are also stable and suitable for fluorination reactions.     

Rotational spectroscopy and molecular structure of 1,1,2-trifluoroethylene and the 1,1,2-trifluoroethylene-hydrogen fluoride complex

Fourier transform microwave rotational spectra in the 6-22 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen fluoride, including the normal isotopomer, the two singly substituted 13C species, and the complex obtained with DF. A unique planar structure for the complex is determined from a combined analysis of the rotational constants derived from the spectra and atomic positions obtained using Kraitchman [Am. J. Phys. 21, 17 (1953)] substitution coordinates. Consistent with this structure, no hyperfine splitting of rotational lines due to the nuclear quadrupole coupling interaction is observed for the D-containing species. Although the primary interaction in the complex is a hydrogen-fluorine hydrogen bond, as is the case for all previously studied Lewis acid-fluoroethylene complexes, the CF2CHF-HF complex adopts a distinctly different geometry in which both the primary and secondary interactions occur between the HF molecule and a F atom and a H atom, respectively, bonded to the same carbon of CF2CHF. The 2.020(41) A hydrogen bond has hydrogen fluoride as the donor and 1,1,2-trifluoroethylene as the acceptor and forms a 109.0(13) degrees C-F...H angle. The secondary interaction between the hydrogen fluoride F atom and the H atom geminal to the acceptor F atom causes the hydrogen bond to deviate 41.6(51) degrees from linearity. Structural comparisons with analogous complexes formed with mono- and difluorinated ethylenes suggest that the primary hydrogen bond strength and the fluoroethylene fluorine atom basicity both decrease with increasing fluorine substitution. In the course of this work, it was necessary to obtain additional rotational spectra for the 1,1,2-trifluroethylene monomer and to improve the precision of the values of the structural parameters for this molecule.     

Continuous determination of hydrogen fluoride in air with the fluoride-selective electrode

Hydrogen fluoride in a standard or sample gas stream at 200 ml min^?1 permeates through a teflon membrane (0.8 μm pore size, 0.08 mm thick) into an absorption solution (citrate/acetate buffer at pH 5.4) flowing at 30 ml min^?1. The fluoride produced is measured with the fluoride-selective electrode. The response time is about 12 min. The absorption efficiency of hydrogen fluoride is about 70% between 6.5 and 0.25 ppm by volume (5.2 and 0.2 mg m^?3). In this range, the Nernst equation is valid with a relative standard deviation of less than 1.8%. The lower determination limit for hydrogen fluoride is 0.1 ppm (0.08 mg m^?3).     

Structure of dense hydrogen fluoride gas from neutron diffraction and molecular dynamics simulations

The gas phase of hydrogen fluoride has been investigated by neutron diffraction experiments at three different particle densities. All investigated states are within the liquid-gas coexistence region of hydrogen fluoride. From the obtained diffraction data we deduced information about the local structure of the gas phase, which consists of small agglomerates. This has been expected as liquid hydrogen fluoride forms the strongest hydrogen bonds known. Molecular dynamics simulations with a modified potential have been carried out for all experimentally investigated states. The results confirmed that the size of the formed agglomerates in the gas phase is growing with increasing density of the gas phase.     

Hydrogen bonding: Part 18. The nature of the OHF hydrogen bond in choline fluoride

The infrared spectrum of the OHF hydrogen bond in choline fluoride is completely different from the spectra of the electrostatic O—H?X hydrogen bonds in the other choline halides; however, this spectrum cannot be accounted for in terms of a “very strong” covalent OHF bond such as those found in carboxylic acid—fluoride ion complexes or postulated for betaine hydrofluoride. The spectrum of choline fluoride is interpreted best in terms of an intermediate type of unsymmetrical hydrogen bond (r° O?F = ～ 256 pm) which shows strong intensity enhancement for the first overtone of the OHF bending vibration.     

Hydrogen fluoride — a suitable solvent for the formation of micelles

Relatively little attention has been paid to nonaqueous polar solvents as media for micellization. The properties of liquid hydrogen fluoride should favor the formation of micelles. The prerequisites for micellization in this solvent and the unique nature of HF are described. Some of the influencing factors like hydrogen bonding, cohesive energy density and Kirkwood-factor are discussed in detail. The CMC-data of selected surfactants in HF determined by solubilization measurements with hydrocarbons are given and discussed.Micelles in hydrogen fluoride. VII, for part VI see [1]     

Phase equilibria for the binary mixtures containing hydrogen fluoride and non-polar compound

Isothermal vapor–liquid equilibria for propane+hydrogen fluoride have been measured. The experimental data are correlated with the association model proposed by Lencka and Anderko for the mixtures containing hydrogen fluoride and the relevant parameters are presented. The recalculated parameters of the association model for pure hydrogen fluoride are presented. The problems occurred in the applications of the association model for the mixtures containing hydrogen fluoride are discussed. The correlation was found to be in good agreement with the experimental data. However, the calculated equilibrium pressures at very diluted compositions of hydrogen fluoride below about 0.01 were shown rather higher than the experimental values.     

A method for the simultaneous detection of hydrogen fluoride and fluorine

A relatively simple and rapid method for detecting hydrogen fluoride and elemental fluorine is described. A solution containing sodium bicarbonate and potassium bromide is treated with the gas. Hydrogen fluoride immediately liberates carbon dioxide from the bicarbonate; elemental fluorine immediately colours the solution and then causes the evolution of oxygen, hydrogen peroxide and hydrogen fluoride. A mixture of fluorine and hydrogen fluoride simultaneously colours the solution and evolves carbon dioxide.     

The possibility of separating hydrogen fluoride from its gaseous mixture with silicon tetrafluoride

We report in this paper investigations of the conditions necessary to effect the selective absorption of hydrogen fluoride from its gaseous mixture with silicon tetrafluoride when that mixture is brought into contact with solid sodium fluoride. Thus, when an anhydrous HF-SiF₄ gas mixture is brought into contact with granular NaF at room temperature only hydrogen fluoride is absorbed (giving NaF·HF), while silicon tetrafluoride remains in the gaseous state. In this way it is possible to separate HF from SiF₄. The hydrogen fluoride may subsequently be regenerated by heating the sodium hydrogen fluoride at 350–400°¹. If, however, the gaseous mixture contains only small traces of water vapor then SiF₄ also reacts with NaF to give Na₂SiF₆ in addition to NaF·HF. Under these circumstances it is not possible to effect a separation.