Trifluoromethanesulphonic acid

Usually, protic acids decompose iV-nitrosoamines189, but recently several salts of N-nitroso compounds with acids have been prepared. Thus, nitrosoamines produce stable salts (1 1) with perchloric and trifluoromethanesulphonic acids which can be isolated, recrystallized and characterized as pure salts. 

Electron-rich aromatic compounds, such as phenol, anisole and A,./V-dimethylaniline, add to bis(2-trichloroethyl) azodicarboxylate under the influence of lithium perchlorate, boron trifluoride etherate or zinc chloride to yield para-substituted products 74, which are transformed into the anilines 75 by means of zinc and acetic acid86. Triflic acid (trifluoromethanesulphonic acid) catalyses the reactions of phenyl azide with benzene, toluene, chlorobenzene and naphthalene, to give TV-arylanilines (equation 34)87. 

Treatment of benzene with trifluoromethanesulphonic acid, followed by trimethylsi-lyl azide, gives aniline in 94% yield. Toluene, o-xylene, mesitylene, chlorobenzene and... 

Similarly, benzene and hydrazoic acid in the presence of a mixture of fluorosulphonic and trifluoromethanesulphonic acid give aniline quantitatively. From toluene 100% of a mixture of o-, m- and p-toluidines is obtained and bromobenzene yields 42% o-bromoaniline and 47% p-bromoaniline, Butyl azide gives iV-butylarylamines under these conditions89. Photolysis of 1-aminoquinolinium perchlorate (76) in aromatic hydrocarbons (benzene, toluene, ethylbenzene or mesitylene) in the presence of 18-crown-6 affords arylamines, e.g. aniline and p-toluidine, by way of the nitrenium ion90 cf Reference 91. 

Treatment of the nitronate salt 397 (from nitroethane and methanolic sodium methoxide) with benzene in the presence of trifluoromethanesulphonic acid gives acetophenone oxime, which is obtained mainly as the (E)-isomer 398433. 

A non-aqueous method for the titration of procaine and other drugs using trifluoromethanesulfonic acid was reported by Zakhari and Kovar [88]. Solutions of procaine hydrochloride in anhydrous acetic acid, acetic anhydride, their mixture, or in acetone, was titrated with an acetic acid solution of 0.1 M trifluoromethanesulphonic acid or 0.1 M perchloric acid. Titration was effected in the presence or in the absence of mercurous acetate. The end point was detected visually (using crystal violet as indicator) or potentiometrically. 

P. Konradsson, D. R. Mootoo, R. E. McDevitt, and B. Fraser-Reid, Iodonium ion generated in situ from AModosuccinimide and trifluoromethanesulphonic acid promotes direct linkage of "disarmed pent-4-enyl glycosides, J. Chem. Soc. Chem. Commun. p. 270 (1990). 

The reduced leaving ability of electron-poor silicon is demonstrated by the reactions of styrene derivatives with trifluoromethanesulphonic acid, as shown in Scheme 3. When the silicon has one or zero electronegative substituents, protiodesilylation takes place. However, when two chloro substituents are present, the loss of the silyl group is disfavoured such that an intramolecular cyclization of the intermediate /J-carbocation 93 takes place116,117. 

Recently, a conceptually different synthesis of MeBmt using an asymmetric glycine aldol reaction was reported by Evans and Weber [29]. The key step consists in the stereochemically controlled condensation of the chiral glycine enolate synthon (23) with the (R)-aldehyde (24) mediated by stannous triflate (tin salt of trifluoromethanesulphonic acid). The desired syn-aldol adduct (25) was isolated in form of the heterocyclic compound (26). The sense of asymmetric induction in the aldol reaction was established by conversion of (26) over three steps into uniform MeBmt (3). 

The allylation of carbonyl compounds with allyltin reagents is still an active area of organotin chemistry from the methodological point of view, and also for synthetic applications. For completeness we should add several alternative techniques, such as the development of trifluoromethanesulphonic acid as a Bronsted acid catalyst for the allylation of aldehydes in water123, or the design of fluorous allyltin reagents for the platinum-catalysed allylation of aldehydes124. 

The same model can be applied to methane- and trifluoromethanesulphonic acids.93 Also in these two cases, there is a linear dependence of 33S Ti on concentration in very large ranges (approximately 0.1-8 M for methanesulphonic acid and 0.1-5 M for trifluoromethanesulphonic acid). Moreover, Ti in methane-sulfonic acid increases linearly with the degree of ionization of the acid. In both cases, 170 Ti has a parallel behaviour. For methanesulphonic acid, T] at infinite dilution is 11.6 ms at 293 K and 13.5 ms at 313 K. For trifluoromethanesulphonic... 

Trifluoromethanesulphonic acid is commercially available and is the most readily obtained member of this series by electrochemical fluorination [202-205] (Figure 8.68), since the yields of perfluoroalkanesulphonic acids decrease as the size of the alkyl group increases. 

Trifluoromethanesulphonic acid forms a very stable crystalline hydrate [205, 218] and reacts vigorously with alcohols, ethers and ketones. Oxonium salts are formed and further reaction may occur on heating (Figure 8.73). 

Solutions of carboxylic acids or anhydrides in strong mineral acids also give rise to the protonation of the weaker component, but often the reaction goes further and leads to the formation of acylium ions. Thus, in the case of acetic acid dissolved in such strong acids as sulphuric, perchloric and trifluoromethanesulphonic acids, dehydration of the protonated species (ACOH2) gives the corresponding acetyl ester and/or its ionised form. The same endproduct is obtained if acetic anhydride is used instead of its acid ... 

Kunitake and Takarabe measured rates of protonation in dichloethane at room temperature using a spectroscopic stop-flow technique with a dead time of about 20 msec. Trifluoromethanesulphonic acid was the proton donor. 1,1-diphenyl-ethylene gave a simple kinetic pattern, [CF3SO3H] = (1—2) x 10 M, [olefin] = (0.7-3) X 10- M, 30 °C, viz. 

The use of ammonia instead of nitromethane in the template condensation with [Co(tame)2] cation gave the macro tricyclic [Co(azatrisartame)]3+ heptazasarcophaginate (yield ca 30%). Like its nitromethane analog, this complex is remarkably stable in aqueous hydrochloric acid. Furthermore, treatment of [Co(azatrisartame)] + cation with trifluoromethanesulphonic acid for several days resulted in a triimine complex (ca 80%) with a ruptured aza-cap, but the methylene units and the four-membered rings remained... 

As opposed to this, the transformation process of the same cyclohexadienone 2 (1 mM) under the same conditions with trifluoromethanesulphonic acid produces a mixture of 2,3,4,6-tetrachlorophenol and pentachlorophenol, by intermolecular and intramolecular processes. 

The crystal structure of trifluoromethanesulphonic acid hemihydrate has been determined.The structure consists of ions, CF3SO3 ions, and CF3SO3H... 

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