Direct fluorination of C

The direct fluorination of C-5 of pyrimidines has been realized by Schroeder, who obtained 2,4,5,6-tetrafluoropyrimidine by treating... 

Type of reaction C-F bond formation Reaction conditions Acetonitrile, room temperature Synthetic strategy Direct fluorination of C(sp )-H group Catalyst Vanadium(III) oxide (V2O3)... 

Cobalt trifluoride is readily prepared by reaction of fluorine (qv) and C0CI2 at 250°C or C0F2 at 150—180°C. Direct fluorination of C0F2 leads to quantitative yields of 99.9% pure CoF (4). 

Niobium Penta.fIuoride, Niobium pentafluoride is prepared best by direct fluorination of the metal with either fluorine or anhydrous hydrofluoric acid at 250—300°C. The volatile NbF is condensed in a pyrex or quartz cold trap, from which it can be vacuum-sublimed at 120°C to yield colorless monoclinic crystals. It is very hygroscopic and reacts vigorously with water to give a clear solution of hydrofluoric acid and H2NbOF ... 

Fluorides. Tantalum pentafluoride [7783-71-3] TaF, (mp = 96.8° C, bp = 229.5° C) is used in petrochemistry as an isomerization and alkalation catalyst. In addition, the fluoride can be utilized as a fluorination catalyst for the production of fluorinated hydrocarbons. The pentafluoride is produced by the direct fluorination of tantalum metal or by reacting anhydrous hydrogen fluoride with the corresponding pentoxide or oxychloride in the presence of a suitable dehydrating agent (71). The ability of TaF to act as a fluoride ion acceptor in anhydrous HF has been used in the preparation of salts of the AsH, H S, and PH ions (72). The oxyfluorides TaOF [20263-47-2] and Ta02F [13597-27-8] do not find any industrial appHcation. 

Titanium Tetrafluoride. Titanium tetrafluoride [7783-63-3] is a white hygroscopic soHd, density 2798 kg/m, that sublimes at 284°C. The properties suggest that it is a fluorine-bridged polymer in which the titanium is six-coordinate. The preferred method of preparation is by direct fluorination of titanium sponge at 200°C in a flow system. At this temperature, the product is sufficiently volatile that it does not protect the unreacted sponge and the reaction proceeds to completion. The reaction of titanium tetrachloride with cooled, anhydrous, Hquid hydrogen fluoride may be used if pure hydrogen fluoride is available. 

Fluorination. Direct fluorination of quinoline was accompanied by extensive fragmentation of the heteroring, but trifluoromethyl hypofluorite in trichlorofluoromethane at -70°C converted 5-fluoro-8-hydroxyquino-line into the 5,7-difluoro-8-hydroxy product (72JMC987). Quinoline, itself, was perfluorinated by fluorine and cobalt(III) fluoride (56JCS783), whereas cesium tetrafluorocobaltate at around 350°C converted it into a mixture of saturated polyfluoro compounds (82JFC413). It is much more satisfactory to introduce fluorine by nucleophilic methods. 

Fluorination. Attention has been focused on the direct fluorination of isoquinolines activated by conversion into 2-methylisocarbostyril (80). With gaseous fluorine (diluted to 10% with argon) in acetic acid a 54% yield of the 4-fluoro derivative was obtained. (Scheme 40). With methylene chloride as the solvent, only the 4-chloro analogue was formed [82H( 17)429]. Fluoroisoquinolines have also been made by displacement of nitro groups, and from diazonium fluoroborates (87JHC181). Hepta-chloroisoquinoline was converted into a perfluoro derivative by heating it in an autoclave with anhydrous potassium fluoride [66JCS(C)2328]. 

H., WiLLE, C., Guber, a.. Direct fluorination of tduene using elemental fluorine in gas/liquid microreactors, J. Fluorine Chem. 105, 1 (2000) 117-128. 

Jahnisch K, Baerns M, Hessel V, Ehrfeld W, Haverkamp V, Lowe H, Wille C, Guber A (2000) Direct Fluorination of Toluene Using Elemental Fluorine in Gas/Liquid Microreactors. J Fluor Chem 105 117-128 Jahnisch K, Hessel V, Lowe H, Baerns M (2004) Chemistry in Microstructured Reactors. Angew Chem Int Ed 43 406 -46 Jensen KF (2001) Microreaction Engineering - is Small Better Chem Eng Sci 56 293-303... 

Carefiil control of the reaction temperature at higher temperatures (627° 3°C) was necessary to reproducibly obtain a completely fluorinated pure white material. A snow-white material was obtained by direct fluorination of graphite at this temperature. Elemental analysis showed the calculated empirical formula to be CF112 003.20... 

Niobium pentafluoride is obtained as an intermediate during the recovery of niobium metal from its ores (See Niobium). It also can be prepared by direct fluorination of niobium metal at 250 to 300°C, either by fluorine gas or anhydrous hydrofluoric acid. The pentafluoride vapors are condensed in a pyrex or quartz tube from which it is sublimed at 120°C under vacuum and collected as colorless crystals. 

Meinert demonstrated that fluorination of pyridine at low temperatures gives the ionic salt N-fluoropyridinium fluoride, a compound that was reported to be explosive at 0°C (Fig. 59) [154]. However, direct fluorination of variously substituted pyridines is possible and good yields of the corresponding 2-fluoro-pyridines (Figs. 60 and 61) [155] are obtained, offering an attractive alternative to the usual halogen-exchange and Balz-Schiemann routes to these products. These reactions probably proceed via N-fluoropyridinium salts (Fig. 62) which are activated towards nucleophilic attack. 

Sulfur tetrafluoride can be prepared by controlled direct fluorination of melted sulfur at 120-200 "C using a 1 10 ratio of fluorine to sulfur20 or by low temperature (— 78 "C) fluorination of powdered sulfur suspended in trichlorofluoromethane.2 ... 

Oxathiazinone dioxides have been used for the synthesis of a new type of heterocyclic N — F reagent 4, which are obtained by direct fluorination of salts of the oxathiazinone dioxide derivatives 3 with a mixture of 5% fluorine in nitrogen at low temperatures.136 137 Isolation of the pure compound 4a or 4b is generally rather difficult and the material is not stable in air at room temperature. In contrast, 3-fluoro-l,2,3-benzoxathiazin-4(3//)-one 2,2-dioxide (4c) is a colorless, thermally stable solid with a melting point of 61 "C.137... 

The pentafluorides are best prepared by direct fluorination of the metals at 250 °C.1,2 Alternative methods include reactions of the metals with HF, CIF3 or BrF3, or SnF2. They have... 

Bis(trifluoromethyl) sulfoxide has been prepared1 previously by the direct fluorination of bis(trifluoromethyl) sulfide at —78°C. in hexafluoroethane followed by hydrolysis of the bis(trifluoro-methyl)sulfur difluoride (difluorobis(trifluoromethyl)sulfur). This method suffers because elemental fluorine must be used, and the yields are low. 

Like SOF2, S02F2 is a colorless gas (bp -58°C). It was first prepared in 1901 by direct fluorination of S02 (133) but has since been prepared by other methods too numerous for them all to be mentioned here. The most successful preparations, however, include the fluorination of S02C12 with SbF3 (134), the reaction of KS02F with chlorine (135), and the thermal decomposition of barium fluorosulfate at 500°C (136). 

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