Fluorination and Addition of Fluorine

Isopropyl Fluoride. The procedure is the same as for ethyl fluoride except that the temperature is k t at 0°, and the ratio of hydrogen fluoride to propylene is held to 1.08. The yield is 61% isopropyl fluoride boils at —10.1°. 

Cyclohexyl Fluoride. In a copper container fitted with inlet, outlet and stirrer is placed 200 g. of anhydrous hydrogen fluoride. After cooling to —35°, 400 g. of precooled cyclohexene is added dropwise over a period of seventy-five minutes. The reaction mixture is poured into a copper beaker filled with cracked ice, stirred, decanted, dried, and distill under 300 mm. pressure (b.p. 71-71.4°). The yield is 60% at 10° it is only 54%. 

2-Difluoropropane (CH3CF2CH3). The vapor of 1 mole of propyne (b.p. —23.3°) is introduced into 4 moles of liquefied hydrogen fluoride in a metal container held at —23° by means of a carbon tetrachloride bath to hich enough solid carbon dioxide has been added to keep it mushy. Care is exercised to prevent the escape of any vapors. The reaction occurs at once. After completion of the addition, the reaction mixture is allowed to warm, and the vapors are passed through water and then condensed in a receiver cooled with solid carbon dioxide. The distillation of the condensate yields 54 g. (64%) of 2,2-difluoroethane, CH3CP2CH3, b.p. 0°. Lower reaction temperatures retard the addition, whereas higher temperatures favor polymerization. 

The direct actiqn of fluorine, first reported by Moissan, has been used to replace hydrogen, to replace another halogen, or to add to a double bond. In very few cases, however, has the reaction been suflB-ciently well controlled to offer a practical method of preparation of organic fluorides. In all cases, several reaction products have been obtained. The procedure has always been performed on a very small scale, and only recently has it been improved to the point where it is not dangerous when the proper precautions are taken. The method has possibilities which still await technical improvements. 

Most organic compoimds bum or explode when brought in contact with fluorine. When the reaction is carried out in a solvent which is immime to fluorine or reacts only slowly with it, care must be taken not 

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The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

Replacement of Halogens by Fluorine and Addition of Fluorine to C = C Bonds with Antimony(V) Fluoride and Fluoroantimonates... 

Treatment of 2,5 and 2,4-furandicarboxylic acids with sulfur tetrafluonde in an excess of hydrogen fluoride leads simultaneously to conversion of the carboxylic groups into trifluoromethyl groups and addition of two fluorine atoms to the furan ring to give highly fluorinated diastereoisomersof2,5-dihydrofuran [225,226,227] (equations 117 and 118)... 

The fluorination of other activated aromatic compounds, such as anisole and phenol, undergo monofluorination mainly in the ortho and para positions, whereas the fluorination of deactivated aromatics, such as nitrobenzene, trifluoromethylbenzene and benzoic acid, give predominantly the corresponding meta fluoro-derivatives which is consistent with a typical electrophilic substitution process. Also, fluoro-, chloro- and bromo-benzenes are deactivated with respect to benzene itself but are fluorinated preferentially in the ortho and para positions [139]. At higher temperatures, polychlorobenzenes undergo substitution and addition of fluorine to give chlorofluorocyclohexanes [136]. 

The fluorination of 2,5-dihydroxybenzo-l,4-quinone and 2-hydroxynaphtho-l,4-quinone results, as well as replacement of the carbonyl oxygen atoms by fluorines, in replacement of the hydroxy groups and addition of a hydrogen fluoride molecule across a C = C bond to give,... 

Oxazolidinones containing the hexafluoroisopropylidene group have been synthesized from a-amino acids and HFA (255, 286). Elimination of hydrogen fluoride from difluoromethyldimethylamine with HFA, and addition of HFA, yield dioxolane 121a, which can be converted with sulfuric acid into the fully fluorinated dioxolanone 120c. The reaction has been described as proceeding via an aminofluoronitrene (164). 

The reaction of a-fluoro-/f-hydroxy-a-phenylsulfanyl esters 4, which can be readily synthesized from aldehydes and ethyl bromofluoroacetate, with diethylaminosulfur triduoride leads to the formation of a,o -difluoro-/I-phenylsulfanyl esters Instead of the expected substitution of the j8-hydroxy group by fluorine, a rearrangement via an episulfonium ion and addition of a fluoride ion % to the ester function gives the a,a-difluorinated product 5. The reaction proceeds under mild conditions with moderate to good yields. In the case of ethyl 2-fluoro-3-hydroxy-3-phenyl-2-(phcnylsulfanyl)propanoate only the nonrearranged product ethyl 2.3-di-fluoro-3-phenyl-2-(phenylsulfanyr)propanoate was isolated. 

The reaction of imines with A-fluorobis(trifluoromethanesulfonyl)amine takes place under mild reaction conditions (22 C. 5 h) and addition of a strong base to generate the inline anion is not necessary. When more than two equivalents of the A-fluoro amine are used, difluoro compounds 3 are formed exclusively (Table 11) however, it is not possible to stop the reaction at the monofluoro stage and, when one equivalent of the fluorinating reagent is used, mixtures of monofluoro 2 and difluoro ketones 3 are obtained. 

The reaction of carbonimidoyl dichlorides with hydrogen fluoride results in replacement of the chloro groups by fluorine and addition of hydrogen fluoride to the C=N group with formation of trifluoromethyl-amines CXIX Upon heating of CXIX in the presence of potassium... 

Substitution of chlorine by, and addition of, hot and thermal F atoms o frflws-CHChCHF have been studied. A study of the rates of fluorination of vinyl fluoride, 1,1-difluoroethylene, and tetrafluoroethylene in the vapour phase using nitrogen-diluted fluorine has indicated that at 291 K the relative rates fall in the ratio 1.00 0.85 0.76, for the respective olefins. ... 

Tetrakis(hexafluoroisopropoxides) of titanium, zirconium, and hafnium have been prepared by the reaction of sodium hexafluoroisopropoxide in an excess of hexafluoroisopropyl alcohol with the anhydrous metal chloride, and the spectroscopic properties are reported. The authors note that, in their experience, application to the Group IV transition metals of the previously published method for metal hexafluoroisopropoxide synthesis gives poor yields of material containing metal, fluorinated alkoxides, and co-ordinated ammonia. Dehydration of the hydrated metal chloride with methyl orthoformate and addition of hexafluoroisopropyl alcohol, followed by passage of dry ammonia through the solution, gives satisfactory yields for yttrium, lanthanum, neodymium, and erbium. 

Preparative Method commercially available. Readily prepared by oxidation of diphenylsilane with Cup2, or by treatment of diphenyldichlorosilane with HF, Znp2, NaBFa, or (NH4)2Sip6. Rate enhancements of the chlorine-fluorine exchange have been achieved with ultrasound and addition of water. Diethoxydiphenylsilane and related structures are converted to diphenyldifluorosilane with 48% HF(aq). ... 

The Knorr pyrrole synthesis was also employed for the synthesis of 3-trifluoropyrroles [91]. Treatment of ethyl trifluoroacetoacetate 267 with sodium nitrite in acetic acid led to the oxime 268. Refluxing with zinc dust and addition of 1,3-dicarbonyl compounds 269 afforded the 3-trifluoromethylpyrroles 270 in moderate yields. Using more acidic trifluoroacetic acid allowed to lower the reaction temperature to 70 °C [92]. Using a similar approach, the tricarboxylic acid ester 273 was prepared starting from the acetone dicarboxylic acid ester 271 and the fluorinated keto ester 272 [93]. 

Ichikawa J (2007) Construction of fluorinated heterocycles intramolecular substitution and addition of fluoro alkenes. Chim Oggi 25(4) 54-57... 

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