Hydrogen fluonde

Using the relationship from the preceding section that the effective electronega tivity of carbon m a C—H bond increases with its s character (sp < sp < sp) the order of hydrocarbon acidity behaves much like the preceding methane ammonia water hydrogen fluonde series... 

Anhydrous hydrogen fluonde Yield based on fluonne The compound is commercially available The compound has considerable vapor pressure... 

Anhydrous hydrogen fluonde The compound is commercially available... 

The hydrofluonnation of alkenes also occurs in the gas phase, generally at somewhat higher temperatures [J]. Huoroethane is obtained m yields as high as 98% at 100 to 160 C by reaction in the presence of minor amounts of higher ot-olefms [6], and 2-fluoropropane is prepared in greater than 90% yield at <.80 "C from hydrogen fluonde and propene in the presence of activated carbon [7]... 

Alkyl and aryl isocyanates react with anhydrous hydrogen fluonde to give carbamyl fluorides [J, 55], the more conveniently handled pyridinium poly(hydro-gen fluoride) reagent can also be used, although the yields tend to be poorer [9] (equation 10). 

Lead tetrafluoride, generated in situ from lead dioxide and hydrogen fluonde, can replace benzylic hydrogen by fluonne [3] Under sirmlar conditions phenol is simultaneously oxidized to 4,4-difluoro-2,5-cyclohexadienone [4 (equations 3 and 4)... 

The tnmethylsilyl enol ether of 1 mdanone (3 2 mmol) in 2 mL of methylene chlonde is added to a mixture of xenon difluonde (4 mmol) and a catalytic amount of pyndimum poly (hydrogen fluonde) m 5 mL of methylene chlonde The mixture IS stured at 0 C for 2 h and poured into dilute sodium bicarbonate solution, tlie organic layer is separated and dned After concentration and column chromatogra phy (silica gel, hexanes), 2-fluoro-1 -mdanone (mp, 59 C) is obtamed in 87% yield... 

Anhydrous hydrogen fluonde, potassium fluonde, and sodium fluonde have all been used to promote the chlorine-fluonne exchangein tetmchloropyrukizine All three fliionne sources replace the chlonne in position 3 first Both sodium and potassium... 

Although both cuprous and cupric fluorides have been studied in the past, an active fluorine donor can be formed from cupric oxide and hydrogen fluonde. This donor, in combination with 2,2 -bipyridine, effectively displaces the halogen of... 

Fluorodediazoniation of alkyl carbamates in hydrogen fluonde/pyndine (70/30) represents a novel route to alkyl fluoroformates [6, 9] (equation 4)... 

A recently discovered variant of the Wallach technique is the silver ion cata lyzed fluorination of aryl diazo sulfides in hydrogen fluonde-pyridine-toluene solvent [57] (equation 12) Electron withdrawing substituents such as acetyl give higher yields of aryl fluoride (71%) than electron donating groups (butyl 39%, methoxy, 2-14%), reductive dediazoniation competes with fluorination... 

Halofluonnation of a-diazoacetophenone by N halosuccmimides in hydrogen fluonde-pyndine provides good yields of a-fluoro-a-haloacetopheiiones [6] (equation 24)... 

Pentafluorophenol is oxidized to different products depending on oxidation agents and reaction condibons The mtermediate is usually pentafluorophenoxy radical, which attacks the aromabc nng to give dimenc and tnmenc products Electrochemical oxidation of pentafluorophenol m hydrogen fluonde solvent and in the presence of a strong Lewis base or acid leads to a different rabo of products [61] (equation 55)... 

Electrochemical oxidation of alkyl aryl ethers results m oxidative dealkylation and coupling of the intermediate radicals ElectrooxidaUon m the presence of hydrogen fluonde salt leads to fluonnated dienones [66] (equation 58)... 

Trifluoromethyl groups are very resistant to hydrolysis, unless they are allylic or benzylic, or vicinal to a carbon linked to hydrogen. In the last case, elimination of hydrogen fluonde leads to the formation of a difluoromethylene group which is key to additional reactions... 

Hydrolysis of A-substituted tnfluoromethyl fluoroformamides leads to A-sub-sdtuted trifluoromethylamines by loss of hydrogen fluonde and carbon dioxide [55] (equation 55). 

These products are thermally stable at room temperature but decompose at elevated temperatures by ehtmnation of CFj The reaction with hydrogen fluonde IS different from that with hydrogen chlonde and hydrogen bromide Presumably this difference is derived from the strength of the boron-fluonne bond [108 (equauon 86)... 

Difluorododecane is unaffected by sodium methoxide in methanol, but its treatment with potassium tert-butoxide in tetrahydrofuran eliminates hydrogen fluonde stereospecifically rneso and dl compounds give, respectively, ( )- and (2) 6 fluoro 6 dodecene [12] (equation 11)... 

Preferential elimination of hydrogen fluonde from vicinal halofluoro compounds occurs also in the cyclohexane series [55 56, 57], acenaphthene series [55], and benzodihydrofuran series [59 60] Here, the strength of the base and the stereochemistry play important roles... 

In l-chloro-2-fluoroacenaphthene [58] and in 2,3-dihalo-2,3-dihydrobenzofuran [59, 60], potassium t rt-butoxide eliminates hydrogen fluonde in preference to hydrogen chloride. trares-2-Chloro-3-fluoro-2,3-dihydrobenzofuran loses hydrogen fluoride quantitatively on treatment with sodamide in tert-butyl alcohol [60] (equation 29). 

Anhydrous hydrogen fluonde is a superior reagent for various cyclizations It converts aryl-substituted diethyl arylmalonates into tetralones in good yields [5] (equation 6)... 

By varying the temperature and the ratio of hydrogen fluonde to tetrachloroethene, the ratio of chloropentafluoroethane to dichlorotetrafluoroethanes can be varied at will The ratio of 1,2-dichlorotetrafluoroethane to 1,1-dichlorotetra-fluorocthane depends upon the temperature of the catalyst, higher temperatures favoring the latter, with yields that can vary from 10 to 50% depending upon operating condidons. 

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