Methyl fluoride-antimony pentafluoride

Methyl fluoride—Antimony pentafluoride—Sulfur dioxide, 3, 201-202. 

Sulphur-Oxygeii-Halogen Compounds.—Chemical analysis of a relatively stable complex of methyl fluoride-antimony pentafluoride, prepared from solution in SO2, showed it to contain bonded SO2. A reinvestigation of the solution of the MeF-SbFs system in SO2 and in SO2CIF revealed that both SO2 and SO2CIF may be O-methylated, giving stable non-exchanging ions (5) and (6). 

The alkylating ability of methyl and ethyl fluoride-antimony pentafluoride complexes has been investigated by Olah et al.,143,144 who showed the extraordinary reactivity of these systems. Self-condensation was observed as well as alkane alkylation. When CH3F-SbF5 was reacted with excess of CH3F at 0°C, at first only an exchanging complex was observed in the H NMR spectrum. After 0.5 h, the starting material was converted into the ferf-butyl cation 4 (Scheme 5.19). 

Lewis Acid Complexes. Sulfolane complexes with Lewis acids, such as boron trifluoride or phosphoms pentafluoride (17). For example, at room temperature, sulfolane and boron trifluoride combine in a 1 1 mole ratio with the evolution of heat to give a white, hygroscopic soHd which melts at 37°C. The reaction of sulfolane with methyl fluoride and antimony pentafluoride inhquid sulfur dioxide gives crystalline tetrahydro-l-methoxythiophenium-l-oxidehexafluoroantimonate, the first example of an alkoxysulfoxonium salt (18). 

When methyl fluoride was absorbed into neat antimony pentafluoride at room temperature a low field band at —12-5 p.p.m. appears. The relative intensity of this species compared with the covalently polarized methyl fluoride complex is, however, small and it could originate from impurities in the system. 

Ethyl fluoride shows more tendency to ionize in antimony pentafluoride, than does methyl fluoride. The solutions in neat antimony pentafluoride are, however, not stable and a rapid formation of t-butyl and t-hexyl cations is observed. This observation indicates self alkylation of ethylene formed in equilibrium of equation (2). 

Alkene- and arenesulphonic acids have been studied in strong or super acid media by NMR spectroscopy. Olah and coworkers64 in 1970 examined sulphonic acids in fluorosulphuric acid-antimony pentafluoride-sulphuryl chloride fluoride solution at low temperature ( — 60 °C). In S02 solution methanesulphonic acid has a chemical shift of <5 3.1 ppm for the methyl group. In the superacid medium there are two singlets at S 4.15 and 4.07, with ratio 60 40, for the methyl protons. It was suggested that this indicated the presence of two isomers, possibly 27 and 28, due to restricted rotation about the SO bond. 

Ene reactions. The antimony pentafluoride—methyl fluoride complex in SO2 undergoes the ene reaction with vinyl halides (1) at -65 to give unsaturated methyl sulfinates (2), isolated after addition of methanol. Yields... 

Electrochemical oxidation of biphenylene and a tetramethyl derivative have been shown to produce dications which have greater stability than the dication from biphenyl [185], Biphenylene and methyl derivatives have been converted into dications by the action of a mixture of antimony pentafluoride and sulphonyl chloride fluoride [186], Their H- and C-n,m.r, spectra indicate that these dications have delocalised lO-ir-electron systems [186],... 

Acylation of alkenes can also be similarly effected with SbFs. Reaction of acetyl fluoride with trifluoroethylene produces 1,1,1,2-tetrafluorohexane-3,5-dione in 40% yield. When antimony pentafluoride is used in excess (more than 6 molar equivalents), 1,1,1,2-tetrafluorobutan-3-one is formed as a side product. Benzoyl fluoride reacts with dilluoroethy lene to form the expected ketone in 39% yield. a, 3-Unsaturated carboxylic acid fluorides have also been used in reactions with perfluoroalkenes. In these cases, a,p-unsaturated ketones are obtained (eq 17). Enol acetates of perfluoroisopropyl methyl ketone and perfluoro-f-butyl methyl ketone react with acetyl fluoride to provide the corresponding p-diketones (eq IS). ... 

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