Fluorosulphonic Acids

H Yajima, Y Kiso, H Ogawa, N Fujii, H Me. Studies on peptides. L. Acidolysis of protecting groups in peptide synthesis by fluorosulphonic acid and methanesulfonic acid. Chem Pharm Bull (Jpn) 23, 1164, 1975. 

When alcohols such as t-butyl alcohol, t-amyl alcohol, t-hexyl alcohol, were dissolved in fluorosulphonic acid-antimony pentafluoride solutions diluted with sulphur dioxide (in order to achieve better mixing of the less viscous solutions and to avoid the possibility of local overheating) at temperatures ranging around — 60°, stable, slightly coloured solutions... 

When solutions of alcohols in fluorosulphonic acid or fluorosulphonic acid-sulphur dioxide were prepared, tertiary carbonium ions could be generally observed, but peak broadening (due to exchange) and side products are observed. Secondary and primary alcohols form generally only the monosulphates. 

Also fluorosulphonic acid protonates phosphine as well as organophos-phines. The phosphonium ions formed are soluble in fluorosulphonic acid. The chemical shifts, 631P and 61, of phosphine, the phosphonium ion and a series of organophosphines and the respective cations obtained by protonation are shown in Table 4. 

Fluorosulphonic Acid, FS02(OH).—This was first obtained by the addition of anhydrous hydrogen fluoride to sulphur trioxidc in a platinum vessel cooled in a freezing mixture, a slight excess of the halogen acid being used and removed subsequently by a current of dry carbon dioxide at about 30° C. 2... 

It is more conveniently prepared by dissolving ammonium fluoride in fuming sulphuric acid and heating, when fluorosulphonic acid distils metallic fluorides may also be used. 

Fluorosulphonic acid is a mobile, colourless liquid, boiling at 162-6° C. it possesses only a slight pungent odour, and has little action on the dry skin. Distillation is accompanied by only very slight decomposition, probably into sulphuryl fluoride and sulphuric acid. Water causes vigorous decomposition dry glass is but slightly affected lead is rapidly converted into lead sulphate and fluoride, whilst with sulphur, sulphur dioxide and hydrofluoric acid arc slowly produced.3... 

Sulphuric acid is oxidised to permonosulphuric, perdisulphuric and fluorosulphonic acids when an ice-cold aqueous solution is treated with fluorine. In addition to the foregoing products, ozone and a very unstable compound believed to be a tetroxide (S04 or S2Os) are also produced.5 A similar oxidation occurs when fluorine is passed into cold solutions of alkali sulphates or hydrogen sulphates. 

Poly(terephthaloyl hydrazide) forms anisotropic solutions in concentrated solutions of some quarternary ammonium hydroxides such as tetramethyl ammonium hydroxide 33). These solutions contain typically about 10% each of the organic base and the polymer. Aromatic polyhydrazides such as poly(chloroterephthaloyl hydrazide) and various co-polyhydrazides also form anisotropic solutions in some of the solvents used for PPT, such as 100% sulphuric acid and fluorosulphonic acid 34). 

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

Cationic cyclization of trienone 276 can be controlled by the choice of the reagent. Thus, fluorosulphonic acid in 2-nitropropane at —70°C afforded a 14 9 1 mixture (70% yield) of cyclic products398, whereas other acidic conditions (95% H2SO4, 85% H3PO4 or SnCLO gave inferior results398,399. 

Mixtures of SbFs and fluorosulphonic acid S02F(0H) are among the most powerful proton-donating media known. Here the SbFs acts as a Lewis acid, as usual, but not as a fluoride acceptor ... 

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. 

We feel that these acids are not particularly suited for fundamental studies, particularly because of their readiness to hydrolyse. However, for those interested in the possible use of fluorosulphonic acid as catalyst we refer to a recent contribution by Goypiron et al. concerning the state of its molecules in the undiluted liquid. This acid homoconjugates readily with its anion ... 

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... 

Methyl fluorosulphonate was obtained by Meyer in 1932 by the action of fluorosulphonic acid on dimethyl ether ... 

Fluorosulphonic Acid. This converts diphenyl chloroarsine into benzene sulphonyl fluoride and the sulphate of diphenyl arsenic acid, 2(CgH5)2As00H.H3S04, melting at 117° C. 

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

---