Reactions with fluorosulphonic acid

Trimethylsilyl fluorosulphonate, generated by in situ reaction of fluorosulphonic acid with either tetramethylsilane or allyltrimethylsilane, has been proposed90 as a cheaper alternative to TMSOTf. 

Cycloheptanes.—Two full papers have appeared on subjects mentioned in Vol. 1 Demole and Enggist s karahanaenone synthesis,and the irradiation of eucarvone. " Another paper concerning the irradiation of eucarvone has appeared in this case the substrate was protonated by carrying out the reaction in fluorosulphonic acid at — 78 °C. The products obtained after quenching the reaction with potassium carbonate in methanol are shown in Scheme 5, together... 

The reaction of alkynes with fluorosulphonic acid at -170 °C has been found to be instantaneous and quantitative. With terminal alkynes, the first step is production of a vinyl cation-fluorosulphonate an ion pair (46). This ion pair subsequently collapses to give the vinyl fluorosulphonate. Experiments with FSO3D showed that the addition is dominantly syn it is probable that collapse of the ion pair gives a syn product, while separation and recombination yields a syn-anti mixture. 

Hindered di-t-aUcylamines RNHBu (R = t-Bu, t-octyl or 1-adamantyl) have been synthesized from t-alkylamines as follows. Reaction with peracetic acid gave the nitrosoalkanes RNO, which were treated with t-butyl radicals, generated from t-butylhydrazine and lead(IV) oxide, to yield t-butyloxyhydroxylamines. Reduction with sodium naphthalide in THF gave the products (equation 12). The di-r-alkyl-amines are inert to methyl iodide and dimethyl sulphate but can be alkylated by methyl fluorosulphonate. ... 

Reaction of HF with S03 gives fluorosulphonic acid HS03F, which is even more strongly acidic than sulphuric acid. In mixtures with S03 and powerful fluoride acceptors such as SbF5 it gives superacid media, which are capable of protonating even most organic compounds. 

Pepper has briefly reported on their activity vis-a-vis styrene, but has never published a full account of his investigation Asami and Tokura used CISO3H in sulphur dioxide for the polymerisation of the same monomer and found it to be a very efficient initiator. Recently, Masuda et al. published a concise study of the polymerisaticMi of styrene by both acids in various solvents. As expected, the chloro derivative was found to be a weaker promoter than the fluorosulphonic acid. Both systems gave asymptotic yields indicating that fast initiation was followed by an important termination reaction. Incorporation of chlorine into the polystyrenes prepared with chlorosulphonic acid (but absence of sulphur) suggested that this acid decomposes in the polymerisation process (hydrolysis ). On the whole, the limited amount of evidence obtained in this study does not allow any mechanistic conclusion. 

In homogeneous solutions, fluorosulphonic acid combined with antimony pentafluoride is used as a superacid having some useful catalytic properties in organic chemistry. In its protonated form, perfluorosulphonic Nafion powders are used as the catalyst for a variety of organic syntheses. The catalytic power is higher than that of other solid phase superacid catalysts. It enables lower temperatures and pressures to be used and its specificity is higher. Nafion is used as the solid superacid catalyst for the gas phase alkalination of aromatic hydrocarbons and liquid phase esterification or Friedel-Craft reactions ... 

Mechanisms have been proposed for the reactions of phosphorus(v) halides with sulphuric acid, chlorosulphonic acid, fluorosulphonic acid, and 25% and... 

The same species seems to be formed in fluorosulphonic acid and 1(X)% sulphuric acid as well . Preliminary results also indicate that reaction 29 occurs with aromatic sulphenyl chlorides. The tendency of sulphur compounds to give species like (2) seems quite general for example, disulphide and sulphenyl chloride in FSO3H or 1(X)% H2SO4 and in SOj with BF3 or SbFg give a species analogous to (2) (equation 30). 

Not many initiators belong to this class even though the halogenoacetic, fluorosulphonic, and other acids are included. A detailed analysis of their polymerization mechanism is obscured by complex formation with monomer and with solvent, by the occurrence of aggregates, and by anion reactions in acids with an unstable anion. In spite of its apparent simplicity, initiation by Bronsted acids has not yet been investigated in detail. The pseudo-cationic polymerization of styrene is an instructive example. 

Various Side-chain Reactions.—2-(2-Thienyl)ethyl isocyanate has been prepared from the corresponding primary amine, carbonyi suiphide, and. S-ethyl chloro-thioformate. Cyclization of 2-(2-thienyl)ethyl isothiocyanate with methyl fluorosulphonate or triethyloxonium tetrafluoroborate gave (178a) and (178b), respectively. The 3-thienyl isomer reacted in the same way. Monoesters of aliphatic dicarboxylic acids and 2-(2-thienyl)ethanol have been prepared in con-... 

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