Hydrogen fluoroalkanes

Carboxylic acids react with xenon difluoride to produce unstable xenon esters The esters decarboxylate to produce free radical intermediates, which undergo fluonnation or reaction with the solvent system Thus aliphatic acids decarboxylate to produce mainly fluoroalkanes or products from abstraction of hydrogen from the solvent Perfluoro acids decarboxylate in the presence of aromatic substrates to give perfluoroalkyl aromatics Aromatic and vinylic acids do not decarboxylate [91] (equation 51)... 

Simple a-fluorosulfides are reduced to the fluoroalkanes by sodium-ethanol [9J (equation 75). Clean conversion of bis(trifluoromethyl) diiulfide to trifluoromethyl mercaptan is accomplished with hydrogen sulfide and ultraviolet irradiation (941 (equation 76). Perfluoroalkanesulfonyl fluondes are converted to the sulfmate salts by hydrazine [95] (equauon 77)... 

Alkyl fluorides are for practical purposes resistant to reduction. In a few instances, where fluorine in fluoroalkanes was replaced by hydrogen, very energetic conditions were required and usually gave poor yields 500, SOI], For this reason it is not difficult to replace other halogens present in the molecule without affecting fluorine. 

A further technique said to be useful on an industrial scale for the ECF conversion of alkanesulphonyl fluoride and tetramethyl sulphone to form per-fluoroalkane sulphonyl fluorides involves the continuous extraction of products from the electrolyte and hydrogen gas stream. The method claims high yields (93%) without recovery problems of prior art [151]. 

The addition of bromine monofluoride to alkenes using equimolar quantities of /V-bro-moamides in excess anhydrous hydrogen fluoride gives the expected l-bromo-2-fluoroalkanes and small amounts (3-8 %) of isomeric 2-bromo-l-fluoroalkanes.29 1-Bromo-2-fluoroheptane can be prepared in 60-77% yield from hept-l-cnc, /V-bromoacetamide and hydrogen fluoride in diethyl ether at — 78"C.30 The bromofluorination of methyl methacrylate (1) with 1,3-di-bromo-5.5-dimethylhydantoin (DBH) and liquid hydrogen fluoride exemplifies this procedure.31... 

Tertiary polyfluoro alcohols, l,l,l,3,3,3-hexafluoro-2-methylpropan-2-ol, 1,1,1,3,3-penta-fluoro-2-methylpropan-2-ol and l,l,3,3-tetrafluoro-2-methylpropan-2-ol, on treatment with sulfur tetrafluoride undergo dehydration to give the respective alkenes 7, but not fluoroalkanes small amounts of byproducts resulting from the addition of hydrogen fluoride to the C = C bond of the resultant alkcncs are also formed.54... 

Reaction of AT-fluorobis(trifluoromethylsulfonyl)amine (Id) with alkenes gives various products, depending on the reaction conditions and the structure of the substrate. In solvents of higher nucleophilicity such as water, acetic acid, aqueous hydrochloric acid, and 70 % hydrogen fluoride/pyridine, a-fluorohydrins or their acetates, a-chloro-fl-fluoroalkanes or a,/ -difluoroal-kanes, e.g. 14. are obtained.146 Reaction of styrene and ( >l-phenylpropene with Id in dich-loromethane/acetic acid gives l-acetoxy-2-fluoro-l-phenylethane and -propane, in 92 and 99 % yield, respectively, the latter product in a ratio (erythrojthreo) 1 l.146... 

Different kinds of alkyl and aryl sulfonates 7 have been transformed to the fluorides 8 under fairly mild conditions with potassium fluoride in polyethylene glycol 400.145 No trace of elimination products, normally found due to attack of a second mole of potassium fluoride on the fluoroalkane eliminating hydrogen fluoride, is observed and the hydrolysis product is present only in 4% yield. No displacement of the tosylate group occurred for neopentyl tosylate. 

Fluoroalkyl iodides are oxidized at the iodine atom by trifluoroperacetic acid3 7- 19 or by a mixture of trifluoroacetic anhydride with hydrogen peroxide the products are [bis(trifluoro-acetoxy)iodo]fluoroalkanes, e.g. oxidation of 1 to 2. The iodine atom oxidized in the reactions can be attached either to a nonfluorinated317 318 or a fluorinated carbon atom.319... 

Fluoroalkyl iodides are oxidized at the iodine atom by trifluoroperoxyacetic add [779, 720] or by a mixture of tnfluoroacetic anhydride and hydrogen peroxide [77iodo]alkanes are formed in almost quantitative yields [116, 117 119]... 

Several examples of telomerisation of fluoroalkanes with various telogens are reported in Table 1. All the telogens employed in telomerisation of hydrogenated olefins [21-24] are also efficient for fluoroalkenes and the system of initiator also works well with these telogens. Consequently, a large variety of cleavages of X-Y bonds is possible these bonds can be located at the chain end or in the... 

A mixture of trifluoroacetic anhydride (82 ml) and trifluoroacetic acid (0.7 ml) was treated dropwise with 60% hydrogen peroxide (6.45 ml) with stirring at 0°C. After 10 min, the substrate (143 mmol of polyfluoroiodoalkane) was added into the mixture and stirring was continued for 1 day at 0°C to room temperature. Evaporation to dryness gave almost quantitatively 1 -[bis(trifluoroacetoxy) iodojpoly-fluoroalkane as a white solid. Benzene (189 mmol) and triflic acid (122 mmol) were added into a mixture of this trifluoroacetate in 1,1,2-trichloro-1,2,2-... 

Fluorinated chromia used to catalyze the isomerization reaction of CHF2CHF2 to CF3CH2F, also exhibited evidence for the importance of chromium in higher oxidation states. FTIR spectroscopic measurements of CO adsorption confirmed the occurrence of Cr4+ and Cr5+ on the surface of chromia catalysts before being used [52]. During the activation, Cr4+ and Cr5+ sites were reduced and enhanced activity of the catalyst was observed. The reaction pathway proposed for isomerization involves the formation of hydrogen fluoride due to the degradation reaction of the fluoroalkane. 

Preparation of Fluoroalkanes from Alkenes with Hydrogen Fluoride/Pyridine General Proccdure ... 

However, in most cases ionic polymerization of the alkene is observed. Only a few examples of the formation of fluoroalkanes have been described. Thus, l-fluoro-3,3-dimethylbutane (2) is obtained in 26 /o yield from the reaction of ethene and 2-methylpropene in hydrogen fluoride. 

Hydrogen iodide is very effective in replacing fluorine by iodine in fluoroalkanes [33] (Figure 5.16b). 

Hydrogen fluoride/pyridine (Olah s reagent) is a convenient and effective fluorination agent.22,23 Solutions of alkenes in tctrahydrofuran react with hydrogen fluoride/pyridine to yield fluoroalkanes (Table 2). 

Tetrafluoroethane is a hydrofluorocarbon (HFC) or hydro-fluoroalkane (HFA) aerosol propellant (contains hydrogen, fluorine, and carbon) as contrasted to a CFC (chlorine, fluorine, and carbon). The lack of chlorine in the molecule and the presence of hydrogen reduces the ozone depletion activity to practically zero. Hence tetrafluoroethane can be considered as an alternative to CFCs in the formulation of metered-dose inhalers (MDIs). It has replaced CFC-12 as a refrigerant since it has essentially the same vapor pressure. Its very low Kauri-butanol value and solubility parameter indicate that it is not a good solvent for the commonly used surfactants for MDIs. Sorbitan trioleate, sorbitan sesquioleate, oleic acid, and soya lecithin show limited solubility in tetrafluoroethane and the amount of surfactant that actually dissolves may not be sufficient to keep a drug readily dispersed. 

Note n, a and are normalized in such a way that their sum gives 1.00 and therefore are only relative numbers. These so-called solvatochromic parameters are useful for the characterization of the selectivity properties of a solvent, see Section 5.2. Solvents of low polarity, from fluoroalkanes to carbon tetrachloride, do notinteract with solutes by dipoles or hydrogen bonds, therefore no solvatochromic parameters can be I isted for them. 

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