Iodine monofluoride

Iodine monofluoride, prepared in situ from the elements, has been recommended for the iodination of deactivated substrates without the need for Friedel-Crafts catalysts (90JOC3553) and may find application with heterocyclic compounds. The corresponding chloride has been used frequently [82CJC554 83ACS(B)345 84CHE492, 84M11 86JHC1849 ... 

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... 

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. 

The aluminum/aluminum triiodide catalyzed addition of iodine monofluoride to perhaloal-kenes with terminal CF2 groups provides high yields of the products in the case of tetra-lluoroethene, chlorotrifluoroethene, hexafluoropropene, and 1,1-dichloro-2,2-difluoroethcne, but rather moderate or low yields for 1,2-dichloro-l,2-difluoroethene, 1-chloro-2,2-di-fluoroethene, and trifluoroethene.9... 

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 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 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... 

Hydrazones of benzophenone, deoxybenzoin, acetophenone, 4-te,r(-butylcyclohexanone. cholestan-3-one, and decan-2-one are also converted into CF2 derivatives in about 70% yield when treated with excess iodine monofluoride.,2 124... 

Although the last method gives satisfactory results, it requires a large excess of iodine monofluoride which has to be prepared from iodine and fluorine just prior to use. Furthermore, most of the unsubstituted hydrazones are rather unstable and undergo transformation into azines which are unrcactive towards iodine monofluoride. O-Methyloximes are also inactive with respect to iodine monofluoride. The procedure with bromine trifluoride is free of such limitations. 

Whereas the difference in the reactivity of RfCH=CHR/ and CF2=C(CF3)2 is marginal, the double bond in PFIB is significantly less reactive towards E+ compared to F-propylene. Most electrophilic reactions of this olefin proceed in a temperature range of 100-200°C. Among known reactions are those with HF, HgF2/HF, sulfur/SbF5, and iodine monofluoride [46] ... 

Iodine monofluoride has much lower reactivity. It adds to TFE at ambient temperature, but reaction with F-propene proceeds at elevated temperature [80] ... 

Another conspicuous difference between [IF] and the real molecule of iodine monofluoride is the ability of the latter to react with substituted or unsubstituted hydra-zones, semicarbazones, DNPs and oximes, with overall conversion of the starting carbonyl into the CF2 group in good yields (equation 1 15)208. 

The compound spontaneously decomposes to give Br2 and BrF3 or BrF5. Iodine monofluoride is so unstable that its existence is somewhat questionable. 

Iodine monofluoride (IF) is unknown except in minute amounts observed spectroscopically. It is apparently too unstable with respect to disproportionation to IF5 and I2 to permit its isolation. The other isolable diatomic compounds have varying degrees of stability with respect to disproportionation and fall in the following stability order, where the numbers in parentheses represent the disproportionation constants for the gaseous compounds and the elements in their standard states at 25°C C1F (2.9 X KT") > IQ (1.8 X 10"3) > BrF (8 X KT3) > IBr (5 X 102) > BrCl (0.34). 

The reaction of hydrazones and their derivatives 1 with iodine monofluoride (IF), prepared from the elements, yields the corresponding gem-difluoro compounds 2 (Table 1). Unsubstituted hydrazones 1 (R = R = H) are usually the most suitable substrates for this transformation. 

The mechanism proposed for this reaction involves initial attack of the electrophilic iodine atom of iodine monofluoride on the basic, amine-like nitrogen, followed by concomitant... 

Table 1. Reaction of Hydrazoiies and Hydrazone Derivatives with Iodine Monofluoride...

Crude hydrazones can be used w ithout further purification in this procedure. This is an important advantage since it is well known that azines, which are unreactive towards iodine monofluoride,are sometimes formed during the purification of hydrazones. Anhydrous reaction conditions are necessary in order to avoid regeneration of the original carbonyl compound which, however, can be recycled. 

As noted above, it is not easy to purify unsubstituted hydrazones. Therefore, reactions of hydrazone derivatives with iodine monofluoride have also been studied (Table 1). A-Methyl-and iV,iV-dimcthylhydrazones react more slowly than unsubstituted hydrazones with iodine monofluoride higher tempteratures are often required for their conversion into ge/w-difluorides (Table 1). The reason for this behavior is that elimination of iodomethane from the intermediates is less favorable (see Scheme 1, R = Me). The use of pure derivatives increases the yield in cases sensitive to hydrolysis (cf. entries 25 and 26). 2,4-Dinitrophenylhydrazones only react with iodine monofluoride at temperatures above O C. The yields are generally lower than in the case of unsubslituted hydrazones, and 2,4-dinitrophenylhydrazones formed from aldehydes are unreaetive. 

Semicarbazones (Table 1, R = CONH2) also react with iodine monofluoride. The gem-difluoro compounds are generally obtained in lower yields than with unsubstituted hydrazones, but the corresponding aldehyde derivatives (entry 16) arc reactive in this case. Finally, in the reaction of tosylhydrazones, gew-difluorides are obtained in only low to moderate yields (entries 4 and 23). 

As already noted, azines are unreactive towards iodine monofluoride however, it has been shown that azines react with bromine trifluoride under mild reaction conditions, yielding ew-difluorides (Table 1). The reagent bromine trifluoride is readily prepared from its elements, although caution should be taken because bromine trifluoride reacts violently with water and acetone. 2,4-Dinitrophcnylhydrazonescan also be used as the hydrazonederivatives in reactions with bromine trifluoride (Table 2). No significant byproducts, unlike the reactions with iodine monofluoride, are obtained in this case. The reactions with bromine trifluoride are not sensitive to the stereochemistry of the C = N bond, and both E- and Z-isomers react with the same efficiency. 

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... 

Only a few examples of reactions of oximes and oxime methyl ethers with iodine monofluoride and bromine trifluoride have been reported (Table 6. entries 6, 8 -12). The yields in these reactions are lower, except in the case of the activated aryl ketone (entry 12). Furthermore, iodine monofluoride does not react with oxime methyl ethers. due to the low basicity of the nitrogen atom. Therefore, these reagents are not good alternatives to the reaction utilizing nitrosonium tetrafluoroborate and pyridinium poly(hydrogen fluoride). 

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). 

In contrast to the chemical oxidation of hydrazones with iodine monofluoride, bromine trifluoride, 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).9 In this case gem-... 

For experimental procedures for fluorinations with iodine monofluoride and bromine trifluoride, see the reactions of hydrazones (Section 1.1.9.1.). 

The reagents for iodine fluoride addition to unsaturated centers are iodine229 or A -iodosuc-cinimide (NIS),221 258 and iodine pentafluoride, hydrogen fluoride,221,258 potassium fluoride, silver(I) fluoride229 278 or ammonium hydrogen difluoride/aluminum trifluoride220 as fluoride ion sources. In addition to the in situ iodofluorinations with iodine monofluoride,l96,22< 227 and (difluoroiodo)methane,194,19 iodofluorination with bis(pyridine)iodonium tetrafluoro-borate219 is described. 

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