Nitronium fluoride

Nitrofluorination of alkenes to give 1 (simultaneous addition of fluorine and a nitro group) can be accomplished by a mixture of anhydrous hydrogen fluoride and concentrated nitric acid,321-323-331-340-341 345 by nitronium fluoride,317,329 by nitronium tetrafluorobor-ate,23,332 338 or by nitronium fiuorosulfatc.339... 

Most mixtures of Friedel-Crafts catalysts are non-homogeneous. However, Olah (37) has found that a homogeneous system can be obtained with TiCU, BF3, PFs and AsFs while using tetramethylene sulphone Sulfolan as a solvent. Nitronium fluoride or chloride can then be formed, e.g. 

Another aspect of my early research in Budapest was in nitration chemistry, specifically the preparation of nitronium tetrafluoroborate, a stable nitronium salt. 1 was able to prepare the salt in a simple and efficient way from nitric acid, hydrogen fluoride, and boron trifluoride. 

Nitronium tetrafluoroborate was first prepared by adding a mixture of anhydrous hydrofluoric acid and boron trifluoride to a solution of dinitrogen pentoxide in nitromethane. Nitric acid can be used in place of dinitrogen pentoxide, and by replacing boron trifluoride by other Lewis-acid fluorides Olah and his co-workers prepared an extensive series of stable nitronium salts. ... 

It is also possible to use more powerful reagents to nitrate thiazoles for example, 2-methylthiazole has been nitrated using nitronium tetrafluorobo-rate and the complex nitrogen dioxide-boron tn fluoride (240). The overall yield is about 50 to 60%. 

Fluorine and nitrogen may be added to olefins with the nitrogen in different oxidation states Fluorine and a nilro group are added by reaction of an olefin with nitryl fluoride [131], nitronium tetrafluoroborate [195] (equation 32), or a combination of nitric acid and hydrogen fluoride [131, 196] (equation 33)... 

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 inflate, which can be isolated as a white crystalline solid Nitronium inflate is a powerful nitrating reagent in inert organie solvents and in tnflic acid or sulfuric acid. It nitrates benzene, toluene, chlorobenzene, nitrobenzene, m-xylene, and benzotn-fluoride quantitatively in the temperature range of-110 to 30 °C with exeeptionally high positional selectivity [87],... 

Nitronium tetrafluoroborate is thermally stable up to 170°. Above this temperature it starts to dissociate into nitryl fluoride and boron trifluoride. 

Nitronium tetrafluoroborate has been prepared by interaction of nitric acid, hydrogen fluoride, and boron fluoride in nitromethane.5 However, mixtures of nitric acid and nitromethane are extremely explosive.6,7 The present modification of the procedure, in which the medium is methylene chloride instead of nitromethane, was developed to avoid this hazard. It has not been published before. 

Nitryl chloride (NO2CI) also adds to alkenes, to give p-halo nitro compounds, but this is a free-radical process. The NO2 goes to the less-substituted carbon. Nitryl chloride also adds to triple bonds to give the expected l-nitro-2-chloro alkenes. The compound FNO2 can be added to alkenes by treatment with HF in HNOa or by addition of the alkene to a solution of nitronium tetrafluoroborate (NOJBF4, see 11-2) in 70% polyhydrogen fluoride-pyridine solution (see also 15-37). 

Nitrones, reaction with olefins, 46, 130 Nitronium tetrafluoroborate, from nitric add, boron trifluoride, and hydrogen fluoride, 47, 56 in nitration of aromatic rings, 47, 60... 

The above book [1] deals, in 26 chapters in 5 sections, with theoretical and practical aspects of the use and safe handling of powerful oxidants and their complementary reactive fuels. Materials include nitrogen pentaoxide, perfluoroam-monium ion and salts, nitronium tetrafluoroborate, hydrazinium mono- and diperchlorates, nitronium perchlorate, tricyanomethyl compounds, difluoramine and its alkyl derivatives, oxygen difluoride, chlorine trifluoride, dinitrogen tetraoxide, bromine trifluoride nitrogen fluorides, and liquid ozone-fluorine system. 

A process known as alkene nitrofluorination has been extensively used for the synthesis of /3-nitroalkyl fluorides. Reagents used generate the nitronium cation in the presence of... 

Nitroacetylenes are generally unstable and very explosive and so they have been little studied. Schmitt and co-workers used the nitrodesilylation of trialkylsilylacetylenes with both nitronium salts and nitryl fluoride to obtain nitroacetylenes. Dinitrogen pentoxide has also been used for the nitrodesilylation of trialkylsilylacetylenes. Nitrodestannylation of allylsilanes has also been reported. " ... 

Numerous Lewis acids promote the formation of nitronium ions when in the presence of nitric acid. Nitric acid-boron trifluoride, and the nitric acid-hydrogen fluoride-boron trifluoride reagents described by Olah are practical nitrating agents the latter provides a convenient preparation of nitronium tetrafluoroborate. Olah reports that nitric acid-magic acid (FSOsH-SbFs) is extremely effective for the polynitration of aromatic substrates. 

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. ... 

Numerous synthetic routes to the dinitramide anion have been reported. Cesium dinitramide (149) has been synthesized via the fluoride-catalyzed /1-elimination of 1-(V,A1-dinitramino)-2-trimethylsilylethane (148) with cesium fluoride the latter prepared by treating 2-(trimethylsilyl)ethyl isocyanate with a solution of nitronium tetrafluoroborate and pure nitric acid in acetonitrile. ... 

Alkyl lV,lV-dinitramines (154) have been prepared from the reaction of the tetraalkylam-monium salts (155) of primary nitramines with nitryl fluoride in acetonitrile at subambient temperature. The same reaction with the primary nitramine or its alkali metal salts yields the corresponding nitrate ester. Treatment of the ammonium, potassium, or lithium salts of primary nitramines (156) with a solution of nitronium tetrafluoroborate in acetonitrile at subambient temperature yield alkyl iV,iV-dinitramines. ° The same reactions in ether or ester solvents enables the free nitramine to be used. The nitrolysis of A-alkylnitramides (157) and N,N-diacylamines with nitronium tetrafluoroborate in acetonitrile, and the nitration of aliphatic isocyanates with nitronium tetrafluoroborate and nitric acid in acetonitrile, also yield alkyl A,A-dinitramines (154). 

Nitronium tetrafluoroborate dissolved in 70% hydrogen fluoride/pyridine is a suitable reagent combination for the preparation of a-fluoro-/i-nitroalkanes from alkenes.31,207 The products are useful precursors for the synthesis of /Tfluoroalkylamines (Table 13). 

Table 13. Nitrofluorination of Alkenes Using 70% Hydrogen Fluoride/Pyridine, Nitronium Tetrafluoro-boratc31...

Nitronium tetrafluoroborate in the presence of pyridine poly(hydrogen fluoride) (PPHF) can be used to substitute chlorine or bromine in adamantanes and other hydrocarbons (see Table 21).90... 

Fluoronitroalkanes can be conveniently prepared by adding an alkene to a solution of nitronium tetrafluoroborate dissolved in pyridinium poly(hydrogen fluoride).94 For example cyclohexene (6) gives 1 -fluoro-2-nitrocyclohexanes (7) in good yields.94... 

The nitronium salts of pentafluoroselenate(IV) and pentafluorotellurate(IV) of composition N02XF5 have been prepared23 from the reaction of selenium or tellurium dioxide with nitryl fluoride. 

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