Trifluoromethyl bromide

Another way to prepare fluorinated sulfides is the photochemical alkylation of sulfides or disulfides by perfluoroalkyl iodides [69, 70, 71] (equations 62-64). Reaction of trifluoromethyl bromide with alkyl or aryl disulfides in the presence of a sulfur dioxide radical anion precursor, such as sodium hydroxymethanesulfi-nate, affords trifluoromethyl sulfides [72] (equation 65). 

Fluorinated sulflnates are prepared from sodium dithionite and liquid per-fluoroalkyl halides [74] (equation 67). For the transformation of the gaseous and poorly reactive trifluoromethyl bromide, it is necessary to use moderate pressure [75] (equation 68) These reactions are interpreted by a SET between the intermediate sulfur dioxide radical anion and the halide The sodium trifluorometh-anesulfinate thus obtained is an intermediate for a chemical synthesis of triflic acid. 

The photochemical introduction of a trifluoromethyl group into aromatic and heteroaromatic rings, such as uracil, can be performed also with trifluoromethyl bromide [/5/] (equation 131)... 

Under Barbier conditions, trifluoromethyl bromide reacts with electrophiles, such as aldehydes, Orkelo esters, activated esters, and anhydrides in the presence of pyridine to give trifluoromethylated compounds [35, 45 46] (equations 34 37)... 

Tnfluoromethanesulfinate can be prepared from the reaction of trifluoromethyl bromide with sulfur dioxide and zinc [50] (equation 41) Similar insertion occurs when perfluoroalkyl iodides are used as precursors (equations 41 and 42)... 

There is another substitution reaction, not involving transition-metal complexes, namely, reaction of trifluoromethyl bromide with sulphur dioxide anion radicals (165) (Andrieux et al., 1990a) (this is an interesting route... 

Other sources of radical CF3, much less expensive than CF3I, have been discovered. These are the anodic oxidation of sodium trifluoroacetate (the decomposition being initated by a hydroperoxide or ruthenium catalyst) and trifluoromethyl bromide (CF3Br) using sodium dithionite as initiating agent. ... 

The production of industrially important perfluoroalkane sulfonic acids is generally accomplished by electrochemical fluorination. This method of preparation remains expensive and proceeds in good yields only for short hydrocarbon chains.30 Recently however, Wakselman and Tordeux have described a chemical method for the preparation of trifluoromethane sulfonic acid.31 The procedure involves reaction of a metal selected from zinc, cadmium, manganese, and aluminum with sulfur dioxide in DMF, followed by the introduction of trifluoromethyl bromide under slight pressure. The intermediate sulfinate is subsequently oxidized by hydrogen peroxide, and then hydrolyzed which leads to formation of the trifluoromethane sulfonic acid. Successful extension of the sulfination process to the modification of PCTFE should result in the formation of a sulfinated polymer which can ultimately be oxidized to give a sulfonic-acid modified polymer. 

Even the poorly reactive trifluoromethyl bromide can react under slight pressure [55, 55] or UV irradiation [64] (equation 56). 

Tris(diethylamino)phosphane (8) reacts with phosphorous trichloride and trifluoromethyl bromide to give bis(diethylamino)trifluoromethylphosphane (9) in 70% yield. 

Trifluoromethyl bromide, produced as a fire extinguishing agent (refs. 12, 13), is much cheaper than the corresponding iodide. Unfortunatly, its reactivity is much lower too. At that time, this bromide was considered as rather inert. 

Thiolates are powerful nucleophilic reagents. However, we observed no reaction when trifluoromethyl bromide is bubbled through a potassium thiophenoxide solution in DMF at room temperature. This failure was in agreement with the inertness reputation of this halide. Assuming that a mechanism involving radical anions (Fig. 4, X = Br) could occur, a minimal concentration of the halide should be necessary to maintain the chain process. In order to increase the amount of trifluoromethyl bromide in solution, we performed the reaction under pressure. Indeed, condensation occurred at room temperature in a glass apparatus under 2-3 bars (Fig. 5) (refs. 16,17). Inhibition of this condensation by nitrobenzene was clearly observed, in agreement with the SET process (Fig 4, X = Br). A similar trifluoromethylation of thiols by trifluoromethyl bromide in liquid ammonia under UV irradiation has also been described (ref. 18). 

In contrast to the carbonyl condensations, where no reaction occurred between the substrate and the metal, an initial attack on zinc by sulfur dioxide in DMF was actually observed. Then, introduction of trifluoromethyl bromide under slight pressure led to the formation of zinc triflinate. 

This condensation with sulfur dioxide is rather peculiar. To the difference with carbonyl electrophiles, sulfur dioxide is more easily reduced than trifluoromethyl bromide. As already pointed out, initial consumption of zinc by this anhydride was obvious, producing the sulfoxylate radical anion which is known to be in equilibrium with the dithionite anion (Fig. 15). Incidentally, this salt mixed with sodium bicarbonate in aqueous acetonitrile was used for the transformation of liquid perhalogenoalkyl halides into their corresponding sulfmates (ref. 24). We have been able to transform the gaseous and poorly reactive trifluoromethyl bromide into sodium trifluoromethanesulfinate. However, the reaction conditions (Fig. 16) (ref. 25) were modified because no transformation occurred in the medium employed for the sulfinato-dehalogenation of the liquid halides. 

For many years now, the reactivity of trifluoromethyl bromide has been underestimated. During the past decade the major breakthrough in this area has been the realisation that trifluoromethylation of organic compounds with this halide can be induced by mild reductants such as thiolates, zinc or sulfoxylate radical anion. Nowadays, a great variety of fluorinated products are available by these new methods sodium triflinate and triflic acid, trifluoromethylated alcohols, trifluoromethyl-containing aromatic compounds, ethyl trifluoropyruvate, trifluoromethylsulfides. ... 

Until now the main application of trifluoromethyl bromide was its use as Halon 1301 in aeronautic ( ref. 13).Unfortunatly, Halons are implicated in the depletion of stratospheric ozone. The participants of the 1992 Montreal Protocol Meeting in Copenhagen agreed to phase out Halon production by the year 1994, except for some essential fire-fighting uses. Research on alternative agents have been initiated in order to find new products with low or zero Ozone Depletion Potential. However, the numerous candidates examined so far present... 

Very. similar behaviour has been reported [292] when zinc atoms are co-condensed with a number of fluoroalkyl iodides at —196°C, the zinc atom inserting into the carbon—iodine bond. The resultant non-solvated fluoro-organic zinc compounds have properties vastly different from those generated by conventional solution-phase techniques, being much more reactive and less stable. It was also shown that methyl iodide and trifluoromethyl bromide are much less reactive towards zinc atoms than is trifluoromethyl iodide. 

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