Bromine monofluoride

Bromine Monofluoride. Bromine monofluoride is red to red-brown (4) and is unstable, disproportionating rapidly into bromine and higher fluorides. Therefore, the measurement of its physical properties is difficult and the values reported in Table 1 are only approximate. The uv-absorption spectmm is available (25). 

Bromine monofluoride [13863-59-7], BrF, can be prepared by the direct reaction of Br2 and F2, but because it readily disproportionates it has never been prepared in pure form (57). However, BrF can be prepared in situ by the reaction of Br2 with AgF in benzene (58) or by the reaction of A/-bromoacetamide and HF in ether (59). BrF adds to simple alkenes at room temperature to give products of trans-addition. Bromine trifluoride [7787-71-5], BrF, can be formed from gaseous fluorine and Hquid bromine (60). Bromine pentafluoride [7789-30-2], BrF, is formed from the reaction of BrF vapor with gaseous fluorine at 200°C (60). The tri- and pentafluorides are commercially available. As strong fluorinating agents they are useful in... 

Fluorination with Bromine Monofluoride and Iodine Monofluoride or Stoichiometric Equivalents (BrF3 + Br2, IF5 + 2I2)... 

Bromine monofluoride or iodine monofluoride can be prepared from the corresponding elements in trichlorofluoromethane at — 781 and — 45 C,2,3 respectively. The compounds are unstable and decompose at low temperatures, iodine monofluoridc at — 14 C2,3 and bromine monofluoride, in part, even at — 78 C.1 Therefore, they are used, without separation and purification, in Freon solutions at low temperatures or, most frequently, as stoichiometric mixtures bromine trifluoride/bromine and iodine pentafluoride/iodine. A solution of iodine monofluoride, obtained by bubbling nitrogen-diluted fluorine gas into a suspension of iodine in trichlorofluoromethane at — 75 C, was used for addition to alkene C = C bonds. The reaction is regioselective and in most cases obeys the Markovnikov rule.4 Iodine monofiuoride prepared in situ reacts quite efficiently with steroidal alkenes.4... 

Bromine monofluoride, which is prepared under similar conditions (trichlorofluoromethane,... 

C), has proven to be too reactive and nonselective towards alkenes. In the presence of 2 % ethanol, bromine monofluoride adds to C = C bonds at controllable rates but bromo ether byproducts arc formed that make the isolation of the desired bromofluoroalkanes difficult. The addition of bromine monofluoride is less regioselective compared to the addition of iodine monofluoride positional isomers are always present in the reaction mixture together with the major Markovnikov-typc addition products. 

Bromine monofluoride and iodine monofluoride react with alkynes in chloroform at... 

When diphenylacetylene dissolved in cold chloroform reacts with iodine monofluoride suspended in trichlorofluoromethane, the iodine atoms in the primary addition product are easily replaced by fluorine to give l,1,2,2-tetrafluoro-1,2-diphenylethane (60%) along with benzil (10%). Since the C —Br bond is stronger than the C —I bond, the reaction of bromine monofluoride with diphenylacetylene gives 1,1-dibromo-2,2-difluoro-1,2-diphenylethane (65%) and benzil (15%). 

The stoichiometric equivalents of bromine monofluoride and iodine monofluoride are obtained by reacting bromine trifluoride with bromine and iodine pentafluoride with 2 equivalents of iodine. A convenient procedure for the preparation of bromine trifluoride from bromine and fluorine has been described.6 Iodine pentafluoride can be obtained by passing fluorine gas over solid7 or molten8 iodine. 

The direction of iodine monofluoride addition to hexafluoropropene and, 1,1-di-fluoroethene suggests an electrophilic reaction mechanism. However, chlorotrifluoroethene gives a mixture of isomers both with iodine monofluoridc and with bromine monofluoride .1 0 The reactions of fluoroalkenes with bromine monofluoride proceed too quickly and for this reason they are conducted in l,l,2-trichloro-l,2,2-trifluoroethane though this hampers the isolation of addition products. 

Table 1. Reactions of Fluoroalkcnes with Stoichiometric Equivalents of Iodine Monofluoride" and Bromine Monofluoride"10...

Pentafluorocthyl iodide is of practical interest, particularly as a precursor of higher perfluoroal-kyl iodides. There are several patents for the preparation of the key compound from tetra-fluoroethene, iodine pentafluoride and iodine at 75-80 C in the presence of catalysts anti-mony(III) fluoride, titanium(lV) chloride, boron trifluoride, vanadium(V) fluoride, niobium(V) fluoride, and molybdenum(Vl) fluoride.11-13 The agents iodine monofluoride" and bromine monofluoride" can add to branched pcrfluoroalkcnes, e.g. perfluoro-2-methylbut-2-ene gives perfluoro-2-iodo-2-methylbutane.1415... 

The equimolar mixture of bromine trifluoride and bromine can be employed for the bro-mofluorination of fluorine-free alkcncs such as (Z)- and( )-l,2-dichloroethene, methyl acrylate and its a-substituted derivatives.1 The reactions are carried out in l,l,2-trichoro-l,2,2-tri-fluoroethane (CFC-113) using a 25-35 % excess of bromine trifluoridc/ bromine. The direction of the bromine monofluoride" addition to multiple bonds in the esters, much as in other electrophilic reactions, depends on the electronic nature of the substituent R. 

The stoichiometric equivalents of halogen fluorides, i.e. chlorine monofluoride, bromine monofluoride and iodine monofluoride, have found a wide application in addition reactions to double bonds. The equivalents are obtained by reacting A -haloamides or free halogens in combination with hydrogen fluoride or its salts as the source of fluoride ions. The reactions proceed under mild conditions at — 80 to 20 "C in anhydrous hydrofluoric acid or diethyl ether, tetrahydro-furan, dichloromethane or chloroform mainly by electrophilic addition with Markovnikov-type regioselectivity (anti addition).26-28... 

The addition of bromine monofluoride to alkenes using equimolar quantities of /V-bro-moamides in excess anhydrous hydrogen fluoride gives the expected l-bromo-2-fluoroalkanes and small amounts (3-8 %) of isomeric 2-bromo-l-fluoroalkanes.29 1-Bromo-2-fluoroheptane can be prepared in 60-77% yield from hept-l-cnc, /V-bromoacetamide and hydrogen fluoride in diethyl ether at — 78"C.30 The bromofluorination of methyl methacrylate (1) with 1,3-di-bromo-5.5-dimethylhydantoin (DBH) and liquid hydrogen fluoride exemplifies this procedure.31... 

The system A -bromoacetamide-hydrogen fluoride adds bromine monofluoride to acetylene derivatives.32 Hex-1-yne. hex-3-yne, 1.4-dichlorobut-2-yne, and phenylacetylene give the corresponding bromofiuoroalkenes, in no case is the addition of a second molecule of bromine monofluoride observed. Hex-1 -yne (3) produces 95% of the (E)- and 5% of the (Z)-isomcr 4. 

The addition of halogen fluorides to C = C bonds in steroids is affected by steric crowding to a greater extent than by electronic factors so that the products may be of the anti-Mar-kovnikov type. In several instances the orientation of the bromine monofluoride addition was shown to depend on reaction conditions resulting cither in 6/ -bromo-5a-fluoro- or 5a-bromo-6/i-fluorosteroids.33... 

The A-bromosuccinimidc-hydrogen fluoride/pyridine system was employed to add bromine monofluoride to chalcones in dimethylformamide with the formation of. mt-2-bromo-3-fluoro-... 

The silver(I) fluoride/bromine and silver(I) fluoride/iodine systems can be exploited for generation in situ and electrophilic addition of "bromine monofluoride and iodine monofluoride to cyclohexene, mcthylenecyclohcxane, styrene, indene, and acenaphthylene.55... 

Boron trifluoride and boron trifluoride-diethyl ether complex can be used as a source of fluoride ions in the presence of hypobromites and hypochlorites, e.g. methyl hypobromitc, tert-butyl hypobromite, methyl hypochlorite in carbon tetrachloride at 25 C. The addition of bromine monofluoride" and chlorine monofluoride" to various alkenes is accompanied by the formation of the corresponding alkoxybromides and alkoxychlorides which hinder the isolation of the halofluorinated products.57 jV-Bromo- and A -chloro-substiluted alkyl- and arylamines. -amides, and -imides, A -chloro-A,-methylamine, A -bromo-A -methylamine, A -chloro-A, /V-dimethylamine, A-bromo-A.A-dimethylamine, ACV-dichloro-A -methylamine, V,fV-dibromo-,V-mcthylaminc, A -bromosuccinimide, -V-chlorosuccinimide, Af-bromoacct-amide, A.A -dichlorourethane, can be used in the reaction instead of the hypohalites. The reactions with various alkenes conducted in dichloromethane at room temperature in the presence of boron trifluoride-diethyl ether complex produce bromofluoro and chlorofluoro addition products in 40-80 % yield. However, the reactions are complicated by the addition of A -halo-succinimides and Af.A-dichlorourcthane to the C = C bonds.58... 

When treated with stoichiometric equivalents of chlorine monofluoride and bromine monofluoride at 0 to 25°C, perfluorobenzonitrile affords perfluoro-NW-dichlorobenzylamine and perfluoro-AW-dibromobenzylamine in 60 and 37% yield, respectively.91... 

Magnesium-mediated elimination of bromine monofluoride has been reported in the reaction of 2-bromo-2-chloro-l,l,l-trifluoroethane with ketones, e.g. reaction of 5 with octan-2-one. 

Chlorine monofluoride, CIF Chlorine trifluoride, CIF3 Bromine monofluoride, BrF Bromine trifluoride, BrF3 Bromine pentafluoride, BrF5 Bromine monochloride, BrCI Iodine trifluoride, IF3 Iodine pentafluoride, IF5 Iodine heptafluoride, IF7 Iodine monobromide, IBr Iodine monochloride, ICI Iodine pentabromide, IBr5 Iodine tribromide, IBr3 Iodine trichloride, ICI3 Iodine pentachloride, ICI5... 

When BrF3 is mixed with bromine, the active species is bromine monofluoride and this can be added to olefins (equation 118)213. Bromine trifluoride also used to prepare compounds with hypervalent heteroatoms, many of them, unattainable otherwise (equation 119)214. A key step in Lemal and coworkers unique synthesis of perfluorocyclopentadiene involved also an oxidative fluorination (equation 120)215. BrF3 can also substitute halogens and was used for the preparation of L-3-fluoroalanine 21 (equation 121)216. 

Bromine monofluoride is much less stable than C1F, although it has been prepared by reaction of the elements diluted with nitrogen ... 

Chlorine monofluoride may be prepared by direct interaction at 220 to 250°C and it is readily freed from C1F3 by distillation, but it is best prepared by interaction of Cl2 and C1F3 at 250 to 350°C. Bromine monofluoride also results on direct reaction of Br2 with F2, but it has never been obtained in high purity because of its ready disproportionation. Iodine monochloride is obtained as brownish-red tablets (J3 form) by treating liquid chlorine with solid iodine in stoichiometric amount, and cooling to solidify the liquid product. It readily transforms to the a form, ruby-red needles. Bromine monochloride is prone to dissociation ... 

Other reagents, such as bromine monofluoride, generated in situ from A -bromosuccinimide and pyridinium poly(hydrogen fluoride) [NBS, (HF) /pyridine] or poly(4-vinylpyridinium) poly(hydrogen fluoride) [NBS, (HF) /PVP], and elemental fluorine, as well as electrochemical methods, have been described for the transformation of hydrazones into. gem-difluoro compounds. 

In the reaction of hydrazones with bromine monofluoride (Table 3), the best yields of fluorinated compounds are obtained with bromine monofluoride generated from NBS, (HF) / pyridine (entries 1-3). No satisfactory results were obtained with A-iodosuccinimide. 

Both hydrazones formed from ketones (Table 3, entries 1-6) and aldehydes (entry 7) react with bromine monofluoride, although the latter yield is low (28 %). Adamantanone azine (entry 8) reacts with bromine monofluoride afl ording the corresponding em-difluoride in high yield (77%). 

Table 3. Reaction of Hydrazones with Bromine Monofluoride"...

This method has an important advantage in that the use ofelemental fluorine in the generation of the reagent bromine monofluoride is not necessary, in contrast to iodine monofluoride generation viile nupra). Anhydrous hydrogen fluoride can also be used, but it has a low boiling... 

In contrast to the chemical oxidation of hydrazones with iodine monofluoridc. bromine tri-fluoride, bromine monofluoride, or elemental fluorine, which provides the corresponding gem-inally difluorinated compounds (vide supra), monofluorination of diaryl ketone hydrazones can be achieved by anodic oxidation in the presence of fluoride ions (Table 5). In this case geni-... 

A mixture of iodine with iodine pentafluoride, or bromine with bromine trifluoride, will add iodine monofluoride or bromine monofluoride respectively to fluorinated aUcenes this constitutes a very convenient route to the corresponding monohalopolyfluoroatkanes [178, 179], which is of considerable importance to the surfactant business (Figure 2.30). CIF3, 240°C... 

Hydrazones can be converted into gc/n-difluorides upon reaction with either fluorine [245], bromine monofluoride (generated in situ) [246] or iodine monofluoride [247], and the reaction of diazoketones with fluorine results in similar transformations [248] (Figure 3.50). 

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