Protonations trifluoromethanesulfonic acid

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

The formylmethyl complex 21 also serves as a source of free acetaldehyde, and one equivalent of trifluoromethanesulfonic acid in CH2CI2 releases it from 21 within one hour at room temperature. Acetaldehyde was identified by its 2,4-dinitrophenylhydrazone (isolated in 42% yield), and was determined directly (48%) by quantitative analysis of its IR v 1716 cm"l absorption. The protonation of 21 presumably generates a n2-vinyl alcohol compound 19 (R=H) [IR observable v 1983 cm" ], which then dissociates acetaldehyde. We have overall converted selectively two carbonyls on CpFe(CO)3+ (1) to acetaldehyde. 

Photoproduct of Dl in solid state. Major photoproduct from Dl in the solid state was isolated by silica gel column chromatography and analyzed by IR and NMR spectroscopy (Figures 2 and 3). NMR spectrum shows that a photoproduct of Dl has the absorption band of the N, N-dimethylamino group (2.86 ppm) and the symmetric absorption band of aromatic protons (6.57-7. 10 ppm). The strong IR absorption of the sulfonyl group (12.10 and 1420 cm-1) can be seen in Figure 3. From NMR and TR spectra, the main photoproduct of the Dl was identified as trifluoromethanesulfonic acid 4-N, N-dimethylaminophenyl ester. 

A schematic diagram of the cation flow method for generating N-acyliminium ion 2 is shown in Fig. 5. A solution of carbamate 1 is introduced into the anodic compartment of electrochemical microflow cell, where oxidation takes place on the surface of a carbon fiber electrode. A solution of trifluoromethanesulfonic acid (TfOH) was introduced in the cathodic compartment, where protons are reduced to generate dihydrogen on the surface of a platinum electrode. A-Acyliminium ion 2 thus generated can be analyzed by an in-line FT-IR analyzer to evaluate the concentration of the cation. The solution of the cation is then allowed to react with a nucleophile such as allyltrimethylsilane in the flow system to obtain the desired product 3. 

The cationic chiral Lewis acids 10, generated from the corresponding oxazaboroli-dines by protonation by trifluoromethanesulfonic acid, are excellent catalysts for the enantioselective reaction of 2-substituted acroleins, a-unsaturated a,p-enones, a-unsaturated acrylic acid esters, and a-unsaturated acrylic acids with a variety... 

Protonation of the A -aryl-Af-(3-triisopropylsilylpropargyl) carbamate 37 with trifluoromethanesulfonic acid generates a (3-silylvinyl cationic intermediate 38 that is attacked by the carbamate carbonyl group (but not the aromatic ring) to give good yields of the 2(3/7)-oxazolone 40 (Fig. 5.9). ... 

In the presence of a cationic initiator such as trifluoromethanesulfonic acid and boron trifluoride etherate, 58, gave a mixture of dimers and higher oligomers. [69] On the basis of structural analyses of the dimers prepared from the racemic and optically active monomers, it was concluded that the cationic oligomerization involved protonation onto the amide nitrogen of 58 followed by selective scission of the C(5)—N(6) bond, while the C(5)—0(8) bond remained intact. 

It is assumed86 that this reaction proceeds via the cationoid intermediates 251 and 252 which are analogous to those described by Zielinski95,96 (equations 48 and 50). The same type of nitrilium intermediates 258 and 259 are assumed to be formed by protonation of vinyl chlorides 255 by trifluoromethanesulfonic acid in the nitrile as a solvent (equation 7i)86133. The highly reactive vinyl cations 262 and 263 are generated from the vinyl triflates 261, obtained from corresponding ketones134. These cations react... 

Activation of a side-chain primary alcohol function with trifluoromethanesulfonic acid anhydride led to exclusive C-alkylation resulting in a cationic ring closure to afford the tetrahydroindoles (A)-584 (Equation 140) <2004T1197>. When R = H the N-Tf-substituted compound (5)-584 was formed as a side product in 18% yield. It was important to conduct the reaction in the presence of 4-methyl-2,6-di-/-butylpyridine as a sterically demanding and effective proton scavenger. 

Bronsted acids stronger than pure (100%) sulfuric acid Hq = —11.9) are classified as super acids [131, 132]. Thus, perchloric acid (HCIO4), fluorosulfonic acid (F—SO3H), and trifluoromethanesulfonic acid (CF3—SO3H) are considered as super acids. Even exceedingly weak basic solvents e.g. carbonyl compounds aromatic, ole-finic, and saturated hydrocarbons) are protonated by these super acids to give the corresponding carbocations [131]. 

It is desired to know the transport number of protons in trifluoromethanesulfonic acid. The actual measurements made were of tritium self-diffusion and the result... 

The simultaneous presence of secondary and tertiary oxonium ions in the polymerization of 1,3-dioxolane initiated with trifluoromethanesulfonic acid was alas shown by trapping a proton (from the secondary oxonium ion) and a carbenium ion (from either the tertiary oxonium ion or the alkoxycarbenium ion) by the ion-trap-ping technique. 

Medium Highly acidic. Sources The ether lone pairs are best, with the aromatic ring a poor second. Sinks Trifluoromethanesulfonic acid (triflic acid) is a very strong acid with an estimated pATa of -15. Acidic Hs None. Leaving groups The ether oxygen, but only if protonated. Resonance forms Only benzene pi bond shift. 

The polymerization can be restarted when the same or a different monomer is added. The use of a different monomer leads to block copolymerization. Within the short residence time in a microflow system at low temperature, the polymer chain was really living. In fact, block copolymerization by adding the second monomer in the microflow system has already been achieved by using a strong proton acid, such as trifluoromethanesulfonic acid (TfOH), as an initiator in a microflow system (see Section 9.4.8). 

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. 

---