Hydrogen fluoride

Liquid hydrogen cyanide, hydrogen cyanide in aqueous solution (hydrocyanic acid), and concentrated vapor are absorbed rapidly through the intact skin and may cause poisoning with little or no irritant effect on the skin itself. The liquid in the eye may cause some local irritation the attendant absorption may be hazardous.  

Genotoxic studies have shown primarily negative results. Carcinogenicity bioassays are not available for hydrogen cyanide.  

The 2003 ACGIH ceiling threshold limit value (C-TLV) for hydrogen cyanide is 4.7 ppm (5 mg/m ) with a notation for skin absorption. 

National Institute for Occupational Safety and Health Criteria for a Recommended Standard. .. Occupational Exposure to Hydrogen Cyanide and Cyanide Salts (NaCN, KCN, and Ca(CN)2). DHEW (NIOSH) Pub No 77-108, pp 37-95, 106-114, 170-173, 178. Washington, DC, US Government Printing Office, 1976 

Gosselin RE, Smith RP, Hodge HC Clinical Toxicology of Commercial Products, Section HI, 5th ed. pp 123-130. Baltimore, MD, Williams Wilkins, 1984 

Hydrogen Fluoride. Anhydrous hydrogen fluoride is generally prepared by action of concentrated sulfuric acid on calcium fluoride Fluorspar ( 98% CaF2). The estimated world production is about 1 million tons mostly to 

Extreme caution should be used in handling anhydrous HF. It can cause severe bums that may not be noticed immediately but will be very painful later HF dehydrates the skin, and F removes Ca2+from tissues and delays healing. Immediate thorough water washing of any exposed skin should be followed by application of calcium gluconate gel or benzalkonium chloride (trade name Zephiran Chloride), and medical attention is essential. 

Stable dialkyl ether poly(hydrogen fluoride) complexes (R20-[HF]n, R = Me, Et, n-Pr) have recently been developed by Prakash, Olah, and colleagues.33 DFT calculations suggest a cyclic poly(hydrogen fluoride) bridged structure. Dimethyl ether-5 HF (DMEPHF) was shown to be a convenient and effective fluorinating agent (see Section 5.10.1). 

Carborane Superacids H(CB11HR X.6). Recently, new carbon superacids, icosahedral carboranes H(CBnHR5X6) (where X = chlorine, bromine or iodine R = H, Me, Cl), have been described by Reed et al.34, whose conjugate base, the carborane anion (CBnHR5X6), is quite inert due to low nucleophilicity. 

In Chapter 1, we arbitrarily defined Lewis superacids as those that are stronger than anhydrous aluminum chloride in their reactivity, the most commonly used Friedel-Crafts catalyst. Of course, Lewis acidity is only a relative term concerning specific bases and involved counterions (association, steric hindrance, etc.). The physical properties of some of the Lewis superacids are given in Table 2.3. 

Hydrogen fluoride is a powerful solvent but its use has been severly restricted both by its reactivity towards glass and silica and by its physiological properties. Experimental techniques have, however, been developed which allow the more widespread use of this interesting solvent. Polytetrafluoroethylene and poly-chlorotrifluoroethylene (the latter being transparent) are now available to handle liquid hydrogen fluoride. Some details have been given in a recent review article.  

It is hard to understand why hydrogen fluoride is considered an acceptor solvent, because the formation of a coordinate covalent link by accepting an electron pair is not possible. Hydrogen fluoride is nevertheless known to accept fluoride ions to give [HF2] ions by a donor-acceptor reaction 

The degree of interaction is high enough to consider this a chemical bond, irrespective its actual nature. 

The nature and the extent of molecular association in liquid hydrogen fluoride is influenced by the presence of ionizing impurities, particularly water. Density, acidity and H-n.m.r. behaviour suggest drastic changes in size and arrangement of the (HF)n-polymers. 

Liquid hydrogen fluoride is a highly acidic substance, showing a much lower proton affinity in the anhydrous state than in aqueous solution. The ionic species formed by autoprotolysis are also associated and comprise a hydrogen-bonded network. The formal self-ionization is usually represented as 

As hydrogen fluoride is tighter than air unlike other combustion products such as HCl or CO, it wiU rise in the air. Thus, even semi-dynamic flare firings wiU not lead to significant ffF concentrations, provided the burn out of the payload is accomplished well above the ground level. 

However, in enclosed space such as radiometric test turmels, incomplete ventilation may result in concentration of HF. The effects of HF are well described in the literature [8] and are based on the necrosis of the living tissue by precipitation of calcium known, which can lead to systemic hypocalcaemia, which can have fatal effects. 

Liquid hydrogen fluoride has a large coefficient of thermal expansion, and temperature increases can result in contaiiuncnt failure if tliere is no room for tlicnnal expansion of the liquid. Thus liquid-full equipment presents a special liaztird. A liquid-full vessel is a vessel tliat is not vented and lias little or 

TABLE 8.5.1 Physical Properties of Hydrogen Fluoride CAS Registry Number 07664-39-3 

Vapor pressure Vapor pressure equation B logP = A T + C Where P = vapor pressure (nuuHg) T = Temperature (°C) A = 7.68098. a constant B = 1,475.60, a constant C = 287.88, a constant 17.8 psia at 77°F 29 

Specific heat of vapor at constant volume 0.55 Btuy(lb-°F) at 68°F 29 

Specific lieat of vapor at constant pressure 2.99Btu/(lb-°F)at69 F 29 

Specific heat of liquid at constant pressure 0.62Btu/(lb-°F)at68T 29 

Liquid surface tension Average coefficient of thermal 10.1 dynes/cm at 32°F 29 

Additional properties useful in determining other properties from physical property correlations  

DOT Proper Shipping Name Hydrogen fluoride, anhydrous 

Anhydrous hydrogen fluoride is available from a number of suppliers with grades ranging from 99.0 percent to 99.96 percent. The major impurities are water H2O) and sulfiir dioxide (SO2). A normal specification for 99.90 mole percent hydrogen fluoride is as follows  

Hydrogen fluoride has a wide variety of uses in a number of different industries. It is used in the chemical industry as an electrolyte in the manufacture of pure fluorine, as a fluorinating agent used to produce inorganic fluorides and fluorocarbons, and in the production of aqueous hydrofluoric acid. 

The aluminum industry uses hydrogen fluoride as a fluoride ion source in the production of aluminum fluoride and cryolite. It is also used as a catalyst in petroleum refining and in the production of uranium hexafluoride used in the production of atomic energy fiiels. 

Compressed Gas Association, Handbook of Compressed Gases Springer Science+Business Media New York 1999 

Perform all work with gaseous hydrogen fluoride, and also with hydrofluoric acid in a fume cupboardl When pouring hydrofluoric acid into a vessel, wear rubber gloves and eye protection or a mask. See that no drops of the acid get onto your skin. Thoroughly wash an affected area with water and put cotton wool wetted with a 10% calcium chloride solution on it. 

See how the prepared hydrofluoric acid solution acts on litmus and zinc. 

Pour a calcium chloride solution into 1 ml of a hydrofluoric acid one. What do you observe  

The fluorides of what metals are soluble in water How can you explain the low degree of dissociation of hydrofluoric acid What is 

Etching of Glass with Hydrofluoric Acid. Cover a glass plate with a layer of paraffin. To do this, lower it into paraffin melted in a porcelain bowl and immediately extract it. Make an inscription with a penknife on the paraffin-coated surface so as to uncover the surface of the glass. Make a small paraffin barrier at the edges of the inscription. Pour a 10% hydrofluoric acid solution onto the paraffin-coated plate and let it stand in a fume cupboard. After one or two hours, wash the solution off the plate and remove the paraffin. What happened to the glass Write the equations of the reactions. 

Preparation of Hydrofluoric Acid. Put 5 g of fluorite and 1 g of gypsum into a Teflon (polytetrafluoroethylene), lead, or copper test tube (why is gypsum added ). Pour 5 ml of a 96% sulphuric acid solution over the mixture, tightly close the test tube with a rubber stopper provided with a Teflon, lead, or copper gas-discharge tube. Lower the end of this tube into a Teflon, lead, copper, or paraffin-coated glass beaker containing 10 ml of water so that it only slightly touches the surface of the water (why ). Put an asbestos sheet between the beaker and the Teflon test tube. To speed up the reaction, it is recommended to immerse the Teflon test tube into a beaker with hot water. Why must the test tube not be heated directly by the flame of a burner  

The fluorine thereby obtained is directly processed further (to uranium hexafluoride, sulfur hexafluoride) or liquefied (b.p. -188°C) and filled into pressure cylinders. Pressure cylinders with mixtures of fluorine and nitrogen, with 10 or 20% by volume of fluorine, are widely marketed (utilized, for example, for the surface fluorination of vehicle fuel tanks). The worldwide fluorine capacity is estimated to be ca. 7.5 10 t/a, of which 60% is in the USA, 25% in Europe and 15% in Japan. Ca. 75% of the fluorine manufactured is utilized in the manufacture of uranium hexafluoride, 22.5% in the manufacture of sulfur hexafluoride and 2.5% in the manufacture of tetrafluoromethane. In 1986 ca. 100 t of fluorine was utilized in the manufacture of fluorographite (high conductivity) for use in batteries. 

USA Japan Belgium France FRG Greece Italy NL Spain GB Mexico 

Manufacture of hydrogen fluoride from fluorspar and sulfuric acid in externally heated rotary tube furnaces 

Industrially hydrogen fluoride is manufactured by the reaction of sulfuric acid with fluorspar (acid grade)  

The small quantities of compounds such as carbonates or oxides (e.g. iron oxide) in the fluorspar also react with the sulfuric acid, necessitating a ca. 5-10% excess of sulfuric acid. Silicon dioxide reacts with the already formed 

The kinetics of neither the photochemical nor the thermal decomposition of this compound have received much attention. Bodenstein et al.53 in 1937 showed that the hydrogen and fluorine reaction could not be photosensitised by chlorine at room temperature. 

The kinetics of the thermal hydrogen-fluorine reaction were studied at 110° by Levy and Copeland54 using a magnesium flow reactor. The reaction was found to be first order in F2 but the rate was independent of both H2 concentration and surface/volume ratio of the reaction zone. They concluded that the reaction was initiated and terminated at the walls. The same authors55 investigated the inhibition of the reaction by oxygen in the same apparatus over the temperature 

In view of the kinetic complexities and the small temperature range, this result should be regarded with caution. 

Jacobs et al.S6 and Blauer57 have studied the thermal dissociation of HF behind incident shock waves in argon. Both workers used an infrared emission toft tab 

Both authors found that the data for reaction (29) better fitted the above expressions rather than the conventional Arrhenius equation. Blauer examined the effect of added F2 and concluded that even in the presence of large amounts of fluorine, the reaction 

In general, hydrofluoric acid is less corrosive than hydrochloric acid because it passivates most metals. However, if these films are destroyed by dilution or something else, severe corrosion in the form of hydrogen bhstering of carbon steel and stress cracking of hardened bolts will occur. 

Specific areas where corrosion is likely to occur include the bottom of the acid rerun tower, the depropanizer tower, the overhead condensers of these towers, the reboiler of the propane stripper, and piping around the acid rerun tower. 

By proper design practices to keep the feed stocks dry, and prescribed maintenance procedures to keep the equipment dry during shut-downs, there will be few corrosion problems with this catalyst 

GIVES OFF VERY POISONOUS VAPOR, CAUSES SEVERE 

Dissolves in water, readily forming hydrofluoric acid.1 

Mercury(II) Oxide. Passing HF into rapidly stirred suspension of mercury(II) oxide may cause violent reaction.2 

Phosphorus Pentoxide (P2O5). Vigorous reaction with P205 below 2(PC.3 Oxides. Arsenic trioxide and calcium oxide incandesce in contact with the liquid.4 

The gas severely irritates the eyes and respiratory system and may cause burns to the eyes. It irritates the skin and painful burns may develop after an interval. The liquid causes severe, painful burns often delayed on contact with all body tissues. Prevent inhalation of gas. Prevent contact with skin and eyes.5 TLV-STEL-C (as F) 3 ppm (2.6 mg/m3).6 

Chemical laser action has so far been restricted to the molecules HF, HC1, HBr and their denterated analogs and to CO. Lasing has also been stated in a brief report to occur in the OH radical produced in the O3/H2 photolysis 105). The pumping scheme is likely to be 

There has been no further information on this laser. 

The hydrogen-fluoride laser, first described by Kompa and Pimentel 122 in 1967 and independently by T. Deutsch 123 , has become the most popular chemical laser system. One might even say without exaggeration 

Other pumping steps are possible, for instance, in chain reactions and with other hydrogen- and fluorine-containing reaction partners. Extremely high gains have been found in this laser 124 . As outlined in Section 8, three types of processes have to be included for a full description of this laser formation of the active HF molecules, relaxation and deexcitation reactions, and radiative processes. Each process has to be considered as function of the vibrational quantum number v and rotational quantum number J. However, even if only the -dependence is included, the set of differential equations describing the temporal behavior of the system includes some sixty rate equations. All the rates in addition are more or less dependent on J. For obvious reasons, no account of the rotational effects has been published so far. In spite of all the rate information that has been accumulated, this aspect has not been explored sufficiently but may be important. The considerable complexity of this laser system calls for very extensive collaboration of theoreticians and experimentalists. 

UF8 + H2(D2, HD)/hv First report of a flash initiated HF laser, empirical study of experimental parameters, quenching by various additives, spectra Kompa, Pimentel Kompa, Parker, Pimentel 122  

In Chapter 23 we discuss the chemistry of compounds containing metal-carbon bonds (organometallic compounds) of which metal carbonyls of the type M (CO) are one group. 

In order to investigate the way in which CO bonds to metals, we must appreciate the electronic structure of the carbon monoxide molecule. 

Before constructing an orbital interaction diagram for CO, we must take note of the following  

The decomposition in argon diluent behind incident shock waves has been observed by measuring the infrared emission from HF for various mixtures over a temperature range 3700—6100°K [114, 115]. The proportionality of emission signal to HF concentration was demonstrated to hold over the temperature interval investigated and for optical densities of 0.01—0.5 atm cm. 

The general reaction scheme for the decomposition of hydrogen halides may be represented by 

Measurements of the initial slope were used to determine and only at the high temperature end of the study was it necessary to correct for the effects of the other reactions. The rate coefficients were fitted to an expression which contained the bond dissociation energy and a temperature dependent pre-exponential factor 

The data have also been fitted to the strict Arrhenius form [116] fed, =1.4x 10 exp(-108,000/i T) 

The remainder of the emission profile has been computed by varying the values for fed, feex,. and fed, within specified limits. The profiles were best fitted using the following values 

We now have to consider which atomic orbital interactions are S3anmetry-allowed and then ask whether the atomic orbitals are sufficiently well energy-matched. First, define the axis set for the orbitals let the nuclei lie on the z axis. Overlap between the H Is and F 2s orbitals is 

It is an attractive solvent for Friedel-Crafts reactions because of its high solubility for aluminium chloride (7.4% w/w at — 8°C). One example from Audrieth s review is shown in equation 12.16. 

Mayr [35] has shown very recently that, for very reactive systems, reaction will proceed without a catalyst. Bromination of phenol is claimed to occur with high / -selectivity [31], but this is unexceptional. A solution of sulphur trioxide in sulphur dioxide is claimed to be an especially mild sul-phonating agent. Sulphonation of toluene gives mainly /7-isomer, with no sulphones. Acylation of hindered alcohols with acid chlorides occurs unusually rapidly at ambient temperature [33] (equation 12.17). 

There appears to be considerable scope for the use of sulphur dioxide as an easily recoverable solvent. 

Over most of the composition range, the acidity of hydrogen fluoride/ water mixtures closely parallels that of sulphuric acid/water [36, 37]. It is a milder solvent in so far as substitutive side reactions analogous to sul- 

In the event that an aqueous workup is required hydrogen fluoride can be separated quantitatively from water if sulphuric acid is used to break the azeotrope. It can be recovered efficiently from dilute aqueous solution by extraction with trioctylamine followed by thermal dissociation of the salt [41]. 

The ground state configurations of H and F are I5 and [He]25 2p respectively. Since Zeff(F) Zeff(H), the F 25 and 2p atomic orbital energies are significantly lowered with respect to the H I5 atomic orbital (Fig. 2.14). 

MOs have more carbon than oxygen character. 

Chemical Symbol HF Synonyms Anhydrous hydrofluoric acid CAS Registry Number 7664-39-3 DOT Classification Corrosive material DOT Label Corrosive 

Hydrogen fluoride is highly corrosive to all living tissue. Contact with liquid anhydrous 

---

Another near resonant process is important in the hydrogen fluoride laser, equation (A3.13.37), where vibrational to vibrational energy transfer is of interest ... 

Quack M and Suhm M A 1998 Spectroscopy and quantum dynamics of hydrogen fluoride clusters Advances in Moiecuiar Vibrations and Coiiision Dynamics, Voi. Hi Moiecuiar dusters ed J Bowman and Z Bai (JAI Press) pp 205—48... 

Dyke T R, Howard B J and Kiemperer W 1972 Radiofrequenoy and miorowave speotrum of the hydrogen fluoride dimer a nonrigid moieouie J. Chem. Phys. 56 2442-54... 

Huang Z S, Jucks K W and Miiier R E 1986 The argon-hydrogen fluoride binary complex an example of a long lived... 

Osgood R M Jr, Sackett P B and Javan A 1974 Measurement of vibrational-vibrational exchange rates for excited vibrational levels (2 v 4) in hydrogen fluoride J. Chem. Phys. 60 1464-80... 

Consider first two substances which have very similar molecules. He, hydrogen fluoride and HCl. hydrogen chloride the first is a Weak acid in water, the second is a strong acid. To see the reason consider the enthalpy changes involved when each substance in water dissociates to form an acid ... 

Silicon tetrafluoride is formed when hydrogen fluoride reacts with silica or a silicate ... 

The hydrogen fluoride is conveniently produced in situ by the action of concentrated sulphuric acid on calcium fluoride ... 

Silicon tetrafluoride is a colourless gas, b.p. 203 K, the molecule having, like the tetrahalides of carbon, a tetrahedral covalent structure. It reacts with water to form hydrated silica (silica gel, see p. 186) and hexafluorosilicic acid, the latter product being obtained by a reaction between the hydrogen fluoride produced and excess silicon tetrafluoride ... 

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

This reaction can be reversed by heating and is a convenient method of obtaining anhydrous hydrogen fluoride from an aqueous solution. 

The bond dissociation energy of the hydrogen-fluorine bond in HF is so great that the above equilibrium lies to the left and hydrogen fluoride is a weak acid in dilute aqueous solution. In more concentrated solution, however, a second equilibrium reaction becomes important with the fluoride ion forming the complex ion HFJ. The relevant equilibria are ... 

However, many substances, notably alcohols, have a greater proton affinity than the hydrogen fluoride molecule, and so behave as bases, for example ethanol ... 

Thus nitric acid behaves as a base in hydrogen fluoride. Hence increases of conductivity when substances dissolve in hydrogen fluoride may be due to acidic or basic behaviour. 

Hydrogen fluoride is the most important compound of fluorine. It is prepared in the laboratory, and on the large scale, by the reaction of calcium fluoride with concentrated sulphuric acid. ... 

The reaction is carried out in a lead retort one suitable for the laboratory can be made from a piece of lead piping, bent like a retort and closed at the shorter end. This is charged with fluorspar and the acid and heated, and the hydrogen fluoride is distilled into a polythene vessel. 

Anhydrous hydrogen fluoride (as distinct from an aqueous solution of hydrofluoric acid) does not attack silica or glass. It reacts with metals to give fluorides, for example with heated iron the anhydrous iron(II) fluoride is formed the same product is obtained by displacement of chlorine from iron(II) chloride ... 

Hydrogen fluoride also effects replacement reactions in organic compounds. For example, carbon tetrachloride yields a mixture of chlorofluoromethanes CCI3F, CCI2F2 and so on. Like all the other hydrogen halides, hydrogen fluoride adds on to olefins, for example ... 

Aqueous hydrogen fluoride is a weak acid (see above) and dissolves silica and silicates to form hexafluorosilicic acid hence glass is etched by the acid, which must be kept in polythene bottles. 

By far the largest use of hydrogen fluoride is in the manufacture of fluorocarbons which find a wide variety of uses including refrigerants, aerosol propellants and anaesthetics. Hydrogen fluoride is also used in the manufacture of synthetic cryolite, Na3AIFg, and the production of enriched uranium. 

---