Hydrogen fluoride hydrofluorination

A polymeric form of the reagent from hydrogen fluoride and poly(4-vinylpyndine) is especially easy to handle [I0 Other tertiary amines can also be employed [II], and a two-phase mixture of hydrogen fluoride-melamine-pentane hydrofluorinates cyclohexene to fluorocyclohexane m 98% yield [12]... 

Fluoromethylketones are obtained by dediazoniative hydrofluorination with anhydrous hydrogen fluoride [91, 92 93] or Olah s reagent [d] (equation 23)... 

The hydrofluorination of alkenes with anhydrous hydrogen fluoride has been already described extensively in Houben-Weyl, Vol. 5/3, pp 100-101. In the case of ethene, the yield of fluoroethane increases on raising the temperature (90°C, 20-25 atm), however, the procedure should be carried out at lower temperatures with higher alkenes because of their tendency to polymerize thus, 2-fluoropropane is formed in 60-75% yield at 0-45 C. Similar procedures have been described for 2-fluorobutane, 2-fluoro-2-methylpropane and 2-fluoro-2-methyl-butane from but-l-ene, 2-methylpropene and 2-methylbut-2-ene, respectively.63 Cyclohexene reacts at — 78 C with hydrogen fluoride to give fluorocyclohexane (70%) at 100 C polymerization is observed.59,60 Two equivalents of hydrogen fluoride to allene are taken up at — 70 C, to form 2,2-difluoropropane (50%).64... 

Branched alkenes and cycloalkenes react more readily. The hydrofluorinations may be carried out advantageously with 70 % hydrogen fluoride/pyridine (Olah s reagent) using tetrahydro-furan as a solvent,10,31 but a homogeneous system forms in this case. Therefore, the workup procedure was carried out by quenching the reaction mixture with ice water and neutralization with sodium hydrogen carbonate hydrofluorinations of various alkenes in this way are described in ref 40. 

Diazoalkanes, diazoketones, and diazoacetates can be fluorinated at 0 C with the loss of nitrogen by treatment with 70 % hydrogen fluoride/pyridine (a,a-hydrofluorinations) in 30-95 % yield.31 133 Furthermore, diazo ketones and diazoacetates when N-halosuccinimide is additionally introduced into the hydrogen fluoride medium.133... 

Another method of producing trifluoromethyl groups242 is the treatment of terminal C12C = C moieties by hydrogen fluoride, e.g. formation of 14.242 This principle of combined addition/ substitution steps is successful at higher temperatures predominant or sole hydrofluorination by hydrogen fluoride takes place at a lower temperature.242 -245... 

Stable dialkyl ether poly(hydrogen fluoride) complexes have been shown to be convenient and effective fluorinating agents.553 Various open-chain and cyclic alkenes undergo hydrofluorination with dimethyl ether-5 HF (DMEPHF) atroom temperature to furnish the corresponding fluoro derivatives in high yields (73-94%) with excellent selectivities. The fluorination of secondary and tertiary alcohols exhibit similar features. Bromofluorination of alkenes can also carried out with DMEPHF in combination with /V-bromosuccinimide. The homologous diethyl ether and dipropyl ether complexes are also suitable for fluorinations. 

Olah and Li2 have prepared a solid form of this reagent by reaction of anhydrous HF with cross-linked poly-4-vinylpyridine. It is comparable to pyridinium poly (hydrogen fluoride) for hydrofluorination of alkenes and alkynes and fluorination of alcohols, but is easier to handle. Work-up of reactions requires only a simple filtration, and the spent reagent can be regenerated with HF for further use. 

There are many examples of the addition of hydrogen fluoride to olefinic hydrocarbons. Fluoroethane (1) is prepared by gas-phase hydrofluorination of ethene under pres-... 

The hydrofluorination of propene to give 2 can be carried out in the liquid phase with hydrogen fluoride or with hydrogen fluoride/pyridine, or in the vapor phase with activated charcoal as catalyst. ... 

The addition of hydrogen fluoride to but-l-ene or but-2-ene gives 2-fluorobutane " - ° the hydrofluorination of 2-methylpropene leads to 2-fluoro-2-methylpropane. ... 

Another highly effective and convenient hydrogen fluoride/amine reagent for the hydrofluorination of alkenes is the solution of 14% melamine in 86% hydrogen fluoride (Table... 

The 5 (or 6) hydrogen fluoride/triethylamine complex can also be used as a mild and selective hydrofluorination agent for preparing tertiary alkyl fluorides. ... 

Allene can be hydrofluorinated with anhydrous hydrogen fluoride to give 2,2-difluoro-propane (4) in 50% yield,... 

Hydrofluorination of alkenes is also possible with solid potassium hydrogen fluoride in the presence of silicon tetrafluoride, for example, the formation of 2-fluoro-2,3-dimcthylbutane, ... 

The addition of hydrogen fluoride across double bonds in unsaturated bicyclic terpenes is accompanied in many cases by rearrangements. Hence, hydrofluorination of camphene with... 

Tri-( -benzoyl-D-glucal is hydrofluorinated with hydrogen fluoride at — 70 C for 20 hours to yield 3,6-di-0-benzoyl-2-deoxy-a-D-n7)o-hexopyranosyl fluoride (5). ... 

The reactivity of halogenated alkenes in the electrophilic hydrofluorination reaction decreases with an increasing number of halogen atoms. Thus polyhaloalkenes are rather resistant to the electrophilic addition of hydrogen fluoride.Therefore, the hydrofluorination needs catalysis, with boron trifluoride(Table 6), tantalum(V) fluoride (Table 5), antimony(V) chloride, niobium(V) fluoride,titanium(IV)chloride or molybdenum(V) chloride. ... 

The reaction of polyfluorinated alkenes with silver fluoride and hydrogen fluoride is another hydrofluorination method. Under certain conditions, perfluoroalkylsilvcr compounds can be isolated. For example, 11 % silver fluoride in acetonitrile reacts with hexafiuoropropene at 25 °C under nitrogen to yield a clear light-yellow solution of [tetrafluoro-l-(trifluoromethyl)-ethyl]silver. The addition of hydrogen chloride in acetonitrile at 0"C yields 1,1.1,2,3,3,3-hepta-fluoropropane. ... 

Alkynes can be hydrofluorinated with the hydrogen fluoride/pyridine reagent. - Tetra-hydrofuran is a highly convenient solvent for this reaction. The reaction products are difluorides with Markovnikov orientation, e.g. 2. ... 

Another highly effective and convenient hydrogen fluoride/amine reagent for the hydrofluorination of alkenes is the solution of 14% melamine in 86% hydrogen fluoride (w/w)46,47 (Table 3). The two-phase mixture of this reagent with pentane or carbon tetrachloride is a suitable system for repeated use47 (Table 4). 

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