Nitronium triflate

Nitric acid-triflic anhydride is a powerful nitrating agent and probably involves nitronium triflate as the active nitrating agent. ... 

A convenient method for the preparation of nitronium tetrafluoroborate involves treating a mixture of absolute nitric acid or an alkyl nitrate " with anhydrous hydrogen fluoride and an excess of boron trifluoride. Pure nitronium triflate can be synthesized by treating triflic anhydride or triflic acid with dinitrogen pentoxide in an inert solvent. Other methods for nitronium salt synthesis are discussed by Olah. ... 

Aromatic hydrocarbons can be converted into nitro compounds via an electrophilic substitution using mixed acid. For example, trinitrotoluene is obtained by the direct nitration of toluene using mixed acid. Other good nitrating agents are N02 BF4 and N020S02CF3 (nitronium triflate) in CH2C12 with ultrasonic activation. 

Tnflic acid is an excellent catalyst for the nitration of aromatic compounds [(S7]. In a mixture with nitnc acid, it forms the highly electrophilic nitronium triflate, which can be isolated as a white crystalline solid Nitronium Inflate is a powerful nitrating reagent in inen organic solvents and in triflic acid or sulfuric acid. It nitrates benzene, toluene, chlorobenzene, nitrobenzene, m-xylene, and benzotri-fluoride quantitatively in the temperature range of-110 to 30 C with exceptionally high positional selectivity [87],... 

Nitronium triflate is approximately 150-fold more reactive than the "more-ordered" nitronium tetrafluoroborate and hexafluorophosphate salts in chlorinated solvents and this is attributed to increased solubility conferred to the nitronium ion by the triflate counterion. (Ref. 27a)... 

Nitration and nitratation. Nitronium triflate is generated in situ from Bu NNOj and TfjO. Adamantane gives 1-nitro- or 1-nitratoadamantane on exposure to this reagent in nitromethane or dichloromethane, respectively. Thus, there is a marked solvent effect. 

The combination of tetraalkylammonium nitrates and Tf20 generates nitronium triflate, which acts as a convenient anhydrous... 

Nitronium triflate (Tf0N02) which is readily generated in dichloromethane from tetramethylammonium nitrate (McqN NOa") and triflic anhydride, can be used as a nitrating agent. Its application for the nitration of methyl thiophene-2-carboxylate afforded 5-nitro- and 4-nitro-substituted isomeric products in 91% combined yield (Scheme 89) [137]. 

Nitration of 2-acetylthiophene and thiophene-2-carbaldehyde in ionic liquid EtNHs NOa promoted by Tf20 gave very high yields of mixtures containing 5-nitrated and 4-nitrated thiophenes in a ratio of 3 2 (Scheme 90) [138]. Formed in situ, nitronium triflate (Tf0N02) provides efficient nitration rmder mild conditions, and, moreover, the ionic liquid can be recovered and reused. 

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