Nitronium trifluoromethanesulfonate

The related nitronium salt, N02 (F3CS03 )2H30, has also been prepared. Nitration Limited experimental data suggest that nitronium trifluoromethanesulfonate is more effective than nitronium tetrafluoroborate (1,742-743) under heterogenous conditions (1,2-dichloroethane), but less effective under homogenous conditions (sulfolane and 1,2-dichloroethane). 

During an investigation on the effect of acids on the regioselectivity of nitration of toluene, Coon, Blucher and Hill found that two equivalents of trifluoromethanesulfonic acid react with 100% nitric acid to yield a while crystalline solid, which is a mixture of nitronium trifluoromethanesulfonate and hydronium trifluoromethanesulfonate [7]. 

Nitronium trifluoromethanesulfonate can also be readily prepared by reaction of N2O5 either trifluoromethanesulfonic anhydride (Vagu-Dolsfcii [ J trifluoromethanesulfonic acid (Eflenberger, [59bJ). The former pure salt free of nitric acid or hydronium triflate. 

The electrophilic substitution is the most characteristic reaction for these classes of compounds. Compound (21) undergoes standard electrophilic aromatic substitution reactions. Thus it forms the 6-bromo compound (58) with A7-bromosuccinimide and 6,7-dibromo compound (72) with the excess of the same reagent. It also forms the 6-nitro compound (67) with copper(II) nitrate trihydrate and 6,7-dinitro compound (68) with excess of nitronium tetrafluoroborate. The bis(trifluoro-acetoxy)thallium derivative (73) was formed from trithiadiazepine (21) and thallium(III) trifluoro-acetate in refluxing acetonitrile. Without isolation, (73) was directly converted into the pale yellow 6-iodo compound (74) with aqueous potassium iodide, into the 6-cyano compound (75) with copper(I) cyanide, and into methyl trithiadiazepine-6-carboxylate (76) with carbon monoxide and methanol in the presence of palladium chloride, lithium chloride, and magnesium oxide. Compound (21) is acetylated in the presence of trifluoromethanesulfonic acid (Scheme 7) <85CC396,87JCS(P1)217, 91JCS(P1)2945>. 

Coon et al. [58] have reported the preparation of aftronium trifluoro-methane sulfonate based on the analogy of the related preparation of the perchlorate or fluoroborate. Hydronium trifluoromethanesulfonate is, however, difficult to separate from the nitronium salt... 

A useful feature of this reagent is that high ratios of ortho to para products are found for some substituted aromatics. Finally, it possible to use nitronium-ion salts for nitration. Nitronium fluoroborate has been extensively studied. The trifluoromethanesulfonate salt is also readily prepared and is an active nitrating... 

A proposed mechanism for this reaction involves the following three steps to generate the nitronium ion. The trifluoromethanesulfonate (triflate) ions act as spectators. The ytterbium cation is believed to be hydrated by the water present in the aqueous nitric acid solution. Nitric acid binds strongly to the hydrated ytterbium cation, as shown in equation 1. A proton is generated, as shown in equation 2, by the strong polarizing effect of the metal. Nitronium ion is then formed by the process shown in equation 3. Although the nitronium ion may serve as the active electrophilic species, it is more likely that a nitronium carrier, such as the... 

Salts containing the nitronium ion can be prepared, and they are reactive nitrating agents. The tetrafluoroborate has been used most frequently," but the trifluoromethanesulfonate can also be prepared readily. Pyridine and quinoline form iV-nitro salts on reaction with N02Bp4. These N-nitro heterocycles in turn can act as nitrating reagents. This is called transfer nitration. ... 

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