Triflic acid strength

Analogously, triflic acid isomenzes n-butane into 2 methylpropane [80, 87] Interestingly, perfluorobutanesulfonic acid, which is of similar strength as triflic acid, does not catalyze the isomerization of n-butane [80]... 

The best alkylation conditions were found to be at an acid strength of about //o 10.7, giving calculated research octane numbers of 89.1 (triflic acid-TFA) and... 

When the hydrocarbon base was hexamethylbenzene (I), which is estimated as 1010 times more basic than benzene (27), the strength of acids such as trifluoromethanesulfonic acid (triflic acid) could be examined (28, 29). The position of the protonation equilibrium (I II, equation 2) was also determined by 13C-NMR spectroscopy. 

Metal triflates can be easily prepared from metal halides and triflic acid at -78 C. They show several unique properties compared with the corresponding metal halides. In an early study, Olah reported the use of boron-, aluminum-, and gallium triflates [M(OTf)J as effective Friedel-Crafts catalysts. In the benzoylation and acetylation of toluene and benzene with acyl chlorides, the relative reactivity is boron triflate > gallium triflate > aluminum triflate, in agreement with the relative acidity strength. 

Experiments indicated that the acid strength of the reaction medium must be H0 = -12 or stronger. Pure triflic acid has been estimated to be about H0 = -14.3 Contamination of the triflic acid by water results in a weakened acid system. When the acid strength drops below H0 = -12, significant quantities of 2,2,2-triphenylacetophenone are produced from the pinacol rearrangement. 

Olah et al. reported the triflic acid-catalyzed isobutene-iso-butylene alkylation, modified with trifluoroacetic acid (TFA) or water. They found that the best alkylation conditions were at an acid strength of about//q = —10.7, giving a calculated research octane number (RON) of 89.1 (TfOH/TFA) and91.3 (TfOH/HaO). Triflic acid-modified zeohtes can be used for the gas phase synthesis of methyl tert-butyl ether (MTBE), and the mechanism of activity enhancement by triflic acid modification appears to be related to the formation of extra-lattice Al rather than the direct presence of triflic acid. A thermally stable solid catalyst prepared from amorphous silica gel and triflic acid has also been reported. The obtained material was found to be an active catalyst in the alkylation of isobutylene with n-butenes to yield high-octane gasoline components. A similar study has been carried out with triflic acid-functionalized mesoporous Zr-TMS catalysts. Triflic acid-catalyzed carbonylation, direct coupling reactions, and formylation of toluene have also been reported. Tritlic acid also promotes transalkylation and adaman-tylation of arenes in ionic liquids. Triflic acid-mediated reactions of methylenecyclopropanes with nitriles have also been investigated to provide [3 + 2] cycloaddition products as well as Ritter products. Tritlic acid also catalyzes cyclization of unsaturated alcohols to cyclic ethers. ... 

Triflic acid was the only acid that caused extensive decomposition of borrer-ine and/or the dimeric products when used at elevated temperatures. Presumably, its strength was sufficient to allow for a variety of reaction pathways and resulted in an intractable mixture of dozens of compormds. If lower temperatures were used, then multiple products were stiU seen, but their formation occurred at a slower rate. 

A very important paper from Hi shimura s school clearly confirms many of the points raised in this discussion. It shows first of all that pseudocationic polymerisation is predominant in media of fairiy low dielectric constant for the polymerisation of styrene by three acids of different strength triflic, medianesulphonic and trifluoroacetic. Up to e = 5, the esters are virtually the only species present and the polymers have a unimodal DP distribution. The second order rate constants derived from the expressioi... 

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