Halogen fluoride

The Manufacture and Use of Fluorine and its Compounds, Oxford University Press, London, 1962. 

Hudlicky, Chemistry of Organic Fluorine Compounds, 2nd revised edition, EUis Horwood, Chichester, 1992. 

Miethen and D. Peters in Houben-Weyl Methods of Organic Chemistry. Vol. ElOa, ed. 

Baasner, H. Hegemann and J.C. Tatlow, Georg Thieme, Stuttgart, 1999, p. 95. 

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The reactivity of fluorine compounds varies from extremely stable, eg, compounds such as sulfur hexafluoride [2551-62 ] nitrogen trifluoride [7783-54-2] and the perfluorocarbons (see Fluorine compounds, organic) to extremely reactive, eg, the halogen fluorides. Another unique property of nonionic metal fluorides is great volatiUty. Volatile compounds such as tungsten hexafluoride [7783-82-6] molybdenum hexafluoride [7783-77-9] ... 

Fluorine forms very reactive halogen fluorides. Reaction of CI2 and F2 at elevated temperatures can produce GIF, CIF, or CIF 3 be obtained from the reaction of Br2 and F2. These halogen fluorides react with all nonmetals, except for the noble gases, N2, and O2 (5). Fluorine also forms a class of compounds known as hypofluorites, eg, CF OF (6). Fluorine peroxide [7783-44-0], O2F2, has also been reported (6). 

The halogen fluorides are binary compounds of bromine, chlorine, and iodine with fluorine. Of the eight known compounds, only bromine trifluoride, chlorine trifluoride, and iodine pentafluoride have been of commercial importance. Properties and appHcations have been reviewed (1 7) as have the reactions with organic compounds (8). Reviews covering the methods of preparation, properties, and analytical chemistry of the halogen fluorides are also available (9). 

The halogen fluorides are best prepared by the reaction of fluorine with the corresponding halogen. These compounds are powerful oxidising agents chlorine trifluoride approaches the reactivity of fluorine. In descending order of reactivity the halogen fluorides are chlorine pentafluoride [13637-63-3] 1 5 chlorine trifluoride [7790-91-2] 3 bromine pentafluoride [7789-30-2], BrF iodine heptafluoride [16921 -96-3], chlorine... 

The physical properties of the halogen fluorides are given in Table 1. Calculated thermodynamic properties can be found in Reference 24. 

Reactions With Metals. AH metals react to some extent with the halogen fluorides, although several react only superficiaHy to form an adherent fluoride film of low permeabHity that serves as protection against further reaction. This protective capacity is lost at elevated temperatures, however. Hence, each metal has a temperature above which it continues to react. Mild steel reacts rapidly above 250°C. Copper and nickel lose the abHity to resist reaction above 400 and 750°C, respectively. 

The rapid reaction of CIF and BrF with metals is the basis of the commercial use in cutting pipe in deep oil weUs (64—68). In this appHcation, the pipe is cut by the high temperature reaction of the halogen fluoride and the metal. 

Halogen fluorides react with sulfur, selenium, teUurium, phosphoms, sHicon, and boron at room temperature to form the corresponding fluorides. Slight warming may be needed to initiate the reactions (4) which, once started, proceed rapidly to completion accompanied by heat and light. The lack of protective film formation aHows complete reaction. 

Water reacts violently with aH halogen fluorides. The hydrolysis process can be moderate by cooling or dilution. In addition to HF, the products may include oxygen, free halogens (except for fluorine), and oxyhalogen acids. 

Fused sHica and Pyrex glass (qv) are not significantly attacked by halogen fluorides up to 100°C if HF is absent. 

Liquid Halogen Fluorides as Reaction Media. Bromine trifluoride and iodine pentafluoride are highly dimerized and behave as ionizing... 

KIFg [20916-97-6] which are both stable, white, crystalline soflds (3,94,95). These compounds dissociate at 200°C to KF and the corresponding halogen fluoride. Other salts are formed similarly (71,95—99). Some of the acids and bases of these systems are Hsted ia Table 2. 

Table 2. Acids and Bases Derived from Halogen Fluorides...

Volatile impurities, eg, F2, HF, CIF, and CI2, in halogen fluoride compounds are most easily deterrnined by gas chromatography (109—111). The use of Ftoroplast adsorbents to determine certain volatile impurities to a detection limit of 0.01% has been described (112—114). Free halogen and haHde concentrations can be deterrnined by wet chemical analysis of hydrolyzed halogen fluoride compounds. 

Equipment should be carefiiUy and completely degreased and passivated with low concentrations of fluorine or the gaseous halogen fluoride before use. Special care should be taken that valves are completely disassembled and each part carefiiUy cleaned. 

Disposal. Moderate amounts of chlorine ttifluoride or other halogen fluorides may be destroyed by burning with a fuel such as natural gas, hydrogen, or propane. The resulting fumes may be vented to water or caustic scmbbers. Alternatively, they can be diluted with an inert gas and scmbbed in a caustic solution. Further information on disposal of halogen fluorides is available (115—118). 

No toxicity data have been reported on the other halogen fluorides, but all should be regarded as highly toxic and extremely irritating to all living... 

Krypton difluoride cannot be synthesized by the standard high pressure-high temperature means used to prepare xenon fluorides because of the low thermal stabitity of KrF. There are three low temperature methods which have proven practical for the preparation of gram and greater amounts of KrF (141—143). Radon fluoride is most conveniently prepared by reaction of radon gas with a tiquid halogen fluoride (CIE, CIE, CIE, BrE, or lE ) at room temperature (144,145). 

Addition of Halogen Fluorides to Unsaturated Systems by Andrew E. Feiring... 

Reagent combinations lor additions of the halogen fluorides to cyclohexene to form trans 1 halo 2 fluorocyclohcxane (equation 1) are shown in Table 1... 

Table 2. Products of Addition of Halogen Fluorides to Norbomene...

Additions of the halogen fluorides to unsaturated steroids [62, 95, 96, 97, 98, 99] and carbohydrates [62, 75] are well known Typical reagent combinations include l,3-dibromo-5,5-dimethylhydantoin (DBH) or the Af-halosuccinimides with hydrogen fluoride Reversal of the expected regiochemistry can be observed with certain steroidal olefins [JOO, 101] (equation 7)... 

Additions of halogen fluorides to the more electrophilic perfluonnated olefins generally require different conditions Reactions of iodine fluoride, generated in situ from iodine and iodine pentafluoride [62 102 103, /05] or iodine, hydrogen fluoride, and parapeiiodic aud [104], with fluormated olefins (equations 8-10) are especially well studied because the perfluoroalkyl iodide products are useful precursors of surfactants and other fluorochemicals Somewhat higher temperatures are required compared with reactions with hydrocarbon olefins Additions of bromine fluoride, from bromine and bromine trifluonde, to perfluonnated olefins are also known [lOti]... 

More general procedures for additions of halogen fluorides to highly fluori-nated olefins involve reactions with a source of nucleophilic fluoride ion, such as an alkali metal fluoride, in the presence of aposttive halogen donor [62 107, lOff, 109, 110, 111] (equations 11 and 12) These processes are likely to occur by the generation and capture of perfluorocarbamonic intermediates Tertiary fluormated carbanions can be isolated as cesium [112], silver [113], or tns(dimethylamino)sul-... 

Carbon-nitrogen multiple bonds in fluorinated imines and nitriles react with halogen fluoride reagents Imines provide 7V-chloroamine.s on reaction with chlo rme fluoride [62, 121, 122, 123] (equations 23 and 24) or with cesium fluoride and chlorine [124] and A -bromoammes on reaction with cesium fluoride and bromine (equation 24)... 

With nitriles, products from addition of one or two equivalents of halogen fluoride can be obtained [725, 726, 127, 128] (equations 25 and 26) on reaction with chlorine fluoride or bromine and an alkali metal fluoride. 

The preparation of e/n-difluoro compounds by the oxidative fluorodesul-furization ot 1,3-dithiolanes readily proceeds by treatment with a pyridinium polyhydrogen fluoride-Af-halo compound reagent the latter serves as a bromonium ion source [2], l,3-Dibromo-5,5-dimethylhydantoin is the most effective of several At-halo oxidants. It is believed that /V-halo compounds combine with hydrogen fluoride to generate in situ halogen fluorides, the oxidants. Formation of gem-difluorides from dithiolanes derived from ketones is efficient and rapid, even at -78 °C, whereas the reaction of dithiolanes derived from aldehydes requires higher temperature (0 °C) (equation 4). 

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