Alkyl fluoride-antimony pentafluoride

C. The Fluorosvlphonic Acid-Antimony Pentafluoride and Hydrogen Fluoride-Antimony Pentafluoride Solvent Systems Attempts to generate simple alkyl-, arylalkyl-, and cycloalkyl-carbonium ions in sulphuric acid or oleum solution generally result in... 

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). 

The reactions of some fluorinated ethers may result in the elimination of alkyl fluorides In the case of 2-methoxyperfluoro-2-butene, treatment with antimony pentafluoride gives perfluoro-3-buten-2-one and methylfluoride [107] By reacting 2-chloro-l,l,2-trifluorodiethyl ether with boron trifluoride etherate or with aluminum chloride, chlorofluoroacetyl fluoride can be obtained with the elimination of ethyl fluonde [108] (equations 76 and 77)... 

The possibility of obtaining stable alkylcarbonium hexafluoro-antimonate salts by interaction of alkyl fluorides with antimony pentafluoride (neat or in sulphur dioxide and later in sulphuryl fluoride or sulphuryl chloride fluoride solution) was then evaluated in detail, extending the investigations to all isomeric C3-, C4-, C5- alkyl fluorides. 

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). 

As mentioned above, previous U.V. studies by Olah et al. (1964) of alkyl fluorides in antimony pentafluoride at room temperature had shown a weak absorption around 290 my, e 500. It must now be... 

The main feature of the proton NMR spectra of alkyl fluorides in antimony pentafluoride is the substantial deshielding of the protons in the carbocations as compared with the starting alkyl fluorides (Figure 3.3 and Table 3.1). 

Typical alkylation reactions are those of propane, isobutane, and n-butane by the ferf-butyl or sw-butyl ion. These systems are somewhat interconvertible by competing hydride transfer and rearrangement of the carbenium ions. The reactions were carried out using alkyl carbenium ion hexafluoroantimonate salts prepared from the corresponding halides and antimony pentafluoride in sulfuryl chloride fluoride solution and treating them in the same solvent with alkanes. The reagents were mixed at —78°C warmed up to — 20°C and quenched with ice water before analysis. The intermolecular hydride transfer between tertiary and secondary carbenium ions and alkanes is generally much faster than the alkylation reaction. Consequently, the alkylation products are also those derived from the new alkanes and carbenium ions formed in the hydride transfer reaction. 

B. The Alkyl Fluoride (Chloride)-Antimony Pentafluoride System. . 309... 

How would we modify the reaction conditions so as to maximize the possibility of generating the carbocation and minimize the chances for its further reaction Antimony pentafluoride (SbFs) is an even stronger Lewis acid than AICI3 toward halogens, particularly fluorine. When SbFs removes a fluoride ion from an alkyl compound the anion antimony hexafluoride (SbFg ) is produced (Fig. 14.109).This anion is nonnucleophilic, and fluoride ion is a poor nucleophile as well. 

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