Methanesulfonic acid, trifluoro-, from

Preparative Method obtained from SbPh3 and trifluoro-methanesulfonic acid, or from 86203 and trifluoro-methanesulfonic acid. ... 

A mixture of the acceptor 43 (10 g, 0.019 mol), the trichloroacetimidate 42 (12 g, 0.025 mol, 1.3 eq) and powdered dry molecular sieves (3 A) in dry EtjO-CH (6 1, 140 mL) [Eq.(16)] was stirred at room temperature, under nitrogen for 20 min. Then trifluoro-methanesulfonic acid (150 p,L, 1.8 mmol, 0.1 eq) was added. After 15 min, the mixture was neutralized with solid NaHCOj and evaporated under reduced pressure. The residue was extracted with toluene-petroleum ether (1 1) and filtered. The solution was evaporated in vacuo. Purification by flash chromatography (toluene-EtOAc, 25 1) yielded 44 (13.8 g, 86%) as a colorless foam, which was crystallized from MeOH mp 157°C, Rf 0.35 (petroleum ether-EtOAc, 8 2), [a]D +59° (c 1, CHC13). 

Hull and Conant in 1927 showed that weak organic bases (ketones and aldehydes) will form salts with perchloric acid in nonaqueous solvents. This results from the ability of perchlonc aad in nonaqueous systems to protonate these weak bases. These early investigators called such a system a superacid. Some authorities believe that any protic acid that is stronger than sulfunc aad (100%) should be typed as a superaad. Based upon this criterion, fluorosulfuric arid and trifluoro-methanesulfonic acid, among others, are so classified. Acidic oxides (silica and silica-aluminai have been used as solid acid catalysts for many years. Within the last few years, solid acid systems of considerably greater strength have been developed and can he classified as solid superacids. 

Dimethoxyacetophenone 97%, anhydrous CH2CI2, and trifluoro-methanesulfonic acid were purchased from Aldrich Chemical Company, Inc., and used as received. 

Also based on an intermolecular hydroxyselenenylation reaction followed by the addition of the OH to an unsaturated group is the selenium promoted conversion of alkenyl nitriles into lactones described by Tiecco [73]. Alkenyl nitriles 107 (Scheme 16) react with PSS 16, generated from diphenyl diselenide and ammonium persulfate, in dioxane and water in the presence of trifluoro-methanesulfonic acid, to afford the hydroxyselenenylation product 108 which is in equilibrium with the protonated molecule 109. Intramolecular addition of the OH group give 110, which is easily hydrolyzed to the final lactone 111. 

The relative strengths of weakly basic solvents are evaluated from the extent of protonation of hexamethylbenzene by trifluoro-methanesulfonic acid (TFMSA) in those solvents or from the effect of added base on the same protonation in solution in trifluoroacetic acid (TFA), the weakest base investigated. The basicity TFA < di-fluoroacetic acid < dichloroacetic acid (DCA) < chloroacetic acid < acetic acid parallels the nucleophilicity. 2-Nitropropane appears to be a significantly stronger base than DC A by the first approach, although in the second type of measurement, the two have essentially equal basicity. The discrepancy is due to an interaction, possible for hydroxylic solvents such as DC A, with the anion of TFMSA. This anion stabilization is a determining factor of carbocationic reactivity in chemical reactions, including solvolysis. A distinction is made between carbocation stability, determined by structure, and persistence (existence at equilibrium, e.g., in superacids), determined by environment, that is, by anion stabilization. 

The a values obtained in this manner have an uncertainty of 0.08 and are listed in Table 3.9 adopted from [3]. Water has a large value of a = 1.17, but certain phenols and halogen-substituted alkanols and carboxylic acids are considerably more acidic hexafluoro-i-propanol has a = 1.96, dichloroacetic add has a = 2.24, and trifluoro-methanesulfonic acid has AN = 131.7, much higher than the value for water, 54.8, but these are rarely used as solvents for electrolytes and therefore are not dealt with further here. 

Reaction of traws-l,3-diphenyl-l-butene (D), the trans ethylenic dimer of styrene, with trifluoro-methanesulfonic acid in dichloromethane has been performed at temperatures lower than room temperature using a stopped-flow technique with real time UV-visible spectroscopic detection. The main product of the reaction was the dimer of D. A transient absorption at 340 nm has been assigned to 1,3-diphenylbutylium, a model for the polystyryl cation. Other absorptions at 349 nm and 505 nm have also been observed and were assigned to an allylic cation, l,3-diphenyl-l-buten-3-ylium, resulting from hydride abstraction from D. This species was very stable at temperatures lower than -30°C. A general mechanism was proposed based on a kinetic study of the reactions involved. 

As mentioned several times Lewis acids are highly valuable catalysts but the most commonly used ones such as aluminium chloride and boron trifluoride are highly water sensitive and are not usually recovered at the end of a reaction, leading to a significant source of waste. In recent years there has been much research interest in lanthanide triflates (trifluoro-methanesulfonates) as water stable, recyclable Lewis acid catalysts. This unusual water stability opens up the possibility for either carrying out reactions in water or using water to extract and recover the catalyst from the reaction medium. 

Several strong protonic acids are commercially available. Trifluoro-methanesulfonic (triflic) acid, fluorosulfonic acid, and perchloric acid may be obtained and stored in a pure state. The first two can be conveniently purified by distillation (b.p. 162° C and 165° C, respectively) [12], perchloric acid is less frequently used due to its oxidative properties and difficulties in handling (explosive). Complex acids HPF6 (HF + PF5) and HSbF6 (HF + SbF5) are available as complexes with ethers. Acids of H + BF30H- type are often the real initiators of polymerization initiated with Lewis acids (e.g., BF3) if water is not rigorously excluded from the system. 

The substitution reactions of amine platinum(IV) complexes is appreciably slower than those of most other inert metal amines, at least in acidic solutions. Consequently, the availability of a relatively labile leaving group, such as trifluoro-methanesulfonate, may have advantages where substitution is required at the sixth site about the pentaammineplatinum(IV) ion. In parallel with reports of other second- and third-row complexes in this chapter, the synthesis of [Pt(NH3)5(0S02Cp3)] from the [Pt(NH3)5Cl]Cl3 precursor is readily achieved. Both are described below. 

Novel secosteroids (336) and (337) have been prepared from the acid-catalysed rearrangements of fluocinonide acetonide (335 R = H) in the presence of trifluoro-methanesulfonic anhydride and trimethylsilyl trifluoromethanesulfonate as catalyst see... 

Lewis adds, such as FeCls and SnCU, initiate polymerization in cooperation with protic adds, resulting from the reaction of those spedes with traces of water or other acid contaminations present in the S3 tem. Indeed, some Lewis acid-protic acid combinations are very effective as initiators. The question whether Lewis adds alone are capable of initiating ROP of siloxanes is still open. Studies of the polymerization of D3 in the presence of sterically hindered substituted pyridine used as a proton trap proved that some nonprotic spedes, such as RC(0)Cl-SbCls complex, ethylboron sesquitrifiate (Et3B2(OTf)3), and certain metal trifiates, can initiate polymerization of this monomer. Trimethylsilyl triflate was considered to be inactive without addition of free trifluoro-methanesulfonic (trifiic) add CF3SO3H (TfOH). However, Jallouli and Saam reported that, after a long induction period, TMSOTf initiated the polymerization of some... 

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