Nitronium .hexafluorophosphate

Pentamethylbenzene and anthracene react very rapidly with nitronium tetrafluoroborate in sulpholan to give cr-complexes, which decompose slowly (see below), and durene behaves similarly with nitronium hexafluorophosphate in acetonitrile. ... 

Olah and coworkers56 found that treatment of dialkyl, arylalkyl and diaryl sulphides with nitronium hexafluorophosphate (or tetrafluoroborate) 32 at —78° in methylene chloride resulted in the formation of sulphoxides in moderate to high yields (Table 3). In the oxidation of diphenyl sulphide which affords diphenyl sulphoxide in 95% yield, small amounts of the ring nitration products (o- and p-nitrophenyl phenyl sulphides) were formed. However, diphenyl sulphone and nitrophenyl phenyl sulphoxide were not detected among the reaction products. 

The kinetics and mechanism of iV-nitration reactions have been reviewed and the nitration of alkanes with nitronium hexafluorophosphate in CH2CI2 or EtN02 has been shown to involve direct electrophilic insertion of NO2+ into C-H and C-C a-bonds. ... 

Commercially available nitronium tetrafluoroborate contains between 5 and 15 % nitroso-nium tetrafluoroborate and is difficult to purify due to its poor solubility in many organic solvents. The synthesis of high purity nitronium tetrafluoroborate has been described." " Nitronium hexafluorophosphate is less widely available but can be purified by recrystallization from nitromethane. ... 

Nitronium salts are efficient and powerful nitrating agents. Nitronium tetrafluoroborate is the most commonly used nitronium salt for nitration and is commercially available as a solid or as a solution in sulfolane in which the ions are highly solvated and exist as an ion pair. Nitronium tetrafluoroborate shows poor solubility in most organic solvents and so the more soluble nitronium hexafluorophosphate is sometimes preferred for nitrations. Olah and co-workers - have studied the nitration of a vast array of aromatics with nitronium salts. Solutions of nitronium salts in aprotic organic solvents are useful for the nitration of acid sensitive or readily oxidized substrates. Nitronium tetrafluoroborate has been used for the... 

The modification consists of using m-MNT dissolved in 96% sulfuric acid, dropwise addn of 25cc/ it of the nitronium ion (2.5 millimoles of nitronium hexafluorophosphate) dissolved in 96% sulfuric acid, and subsequent quenching of the reaction soln on ice... 

Remarkably, nitronium salts have been shown to react even with methane under superacidic conditions.106 Nitronium hexafluorophosphate (NO2PF6.) reacts with methane, albeit in low yields, when the reaction is carried out in the presence of boron tris(triflate) in triflic acid (eq 63). 

Oxidation of the cyclic selenides 61 and 119 by sulfuric acid or nitronium hexafluorophosphate has provided selenurane salts 2 and 62 (Equation 26) <1996T10375>. 

Miscellaneous reactions. The sulfides are oxidized by an excess of e.g. hydrogen peroxide or 3-chloroperoxybenzolc acid to the corresponding sulfones. A controlled addition of peroxide yields a mixture of sulfoxide and sulfone products. The use of nitronium hexafluorophosphate or tetrafluoroborate to oxidize dlalkyl, aryl alkyl or dlaryl sulfides yields only the corresponding sulfoxide under extremely mild conditions (224). Sulfoxides may be further oxidized to the corresponding sulfones In good yield by the nitronium salts as well (225). 

Diselenoniabicyclo[3.3.0]octane hexafluorophosphates were prepared by reaction of 1,5-diselenacyclooctane with nitronium hexafluorophosphate <89CC1789, 90TL6375). 2,2,8,8-Tetra-deuterated salts have also been synthesized <93T1605>. 

The Reaction of Aromatic Amines with Nitronium Hexafluorophosphate in Nitromethane... 

The preliminary experiments were carried out using both nitronium tetrafluorophosphate in sulpholane and nitronium hexa-fluorophosphate in nitromethane. However, the products from these experiments had unexpectedly high concentrations of nitroso compounds this was traced to significant amounts of nitrosonium salts in the supposedly pure nitronium salts. A method was devised for the purification of nitronium hexafluorophosphate (see Experimental) which, from the raman spectra, was completely effective in removing this impurity. The same method did not work well for nitronium tetrafluoroborate and so all subsequent work was carried out using the hexafluorophosphate salt. 

Product composition for the reactions of aromatic amines with nitronium hexafluorophosphate in nitromethane... 

The fact that 2, 4-dinitroaniline and 2, 3-dinitroaniline react with nitronium hexafluorophosphate in nitromethane to give essentially quantitative yields of the N-nitro compounds (Table 1, exp. A, B) is in accord with previous work in other media (4). 

The formation of significant amounts of C-substituted products in the reaction of 4-nitroaniline with nitronium hexafluorophosphate can be explained in the same way (Table I, exp. E)i Here there is no doubt that reaction should be fast in comparison with the mixing of the solutions for this amine is known to react on encounter with the nitronium ion ( ). This should give rise to regions of enhanced acidity which could lead both to rearrangement of the nitramine and further substitution as illustrated for the reaction of the nitramine itself in exp. P. With 4-nitroanilin the amount of the N-substituted product exceeds that of the C-substituted product and increases as the reactants are diluted (exp. P) and when the efficiency of mixing is improved (exp. G). 

Nitronium tetrafluoroborate, nitronium hexafluorophosphate and nitrosonium tetrafluoroborate were obtained from Ozark-Mahoning Company. 

Purification of Nitronium Hexafluorophosphate. Commercial nitronium hexafluorophosphate (A, 17, 7 g) was dissolved in nitromethane (170 ml) and methylene chloride (170 ml) was added. The precipitated salt (B) was filtered and part removed for the determination of its purity. The remaining precipitate was dissolved in nitromethane (150 ml) and methylene chloride (150 ml) added to the solution. The reprecipitated salt (C,... 

Products. The product analyses for the reaction of nitronium hexafluorophosphate with aromatic amines were carried out by n. m. r. A solution of the nitronium salt and trinitrobenzene (as a standard material for n. m. r. analysis) in nitro-methane was added dropwise, with shaking, to a solution of an amine in the same solvent. After fifteen minutes the reaction mixture was poured into ether (50 ml), and any precipitate filtered off using a glass filter. The precipitate was dissolved in a small amount of acetone and analysed for the diazonium salt by n. m. r. The ether solution was washed with water, dried on magnesium sulphate and filtered using a filter paper. After evaporation of the solvent under reduced pressure, the products were dissolved in acetone or deuterated chloroform and analysed by n. m. r. 

NTFB = nitronium tetrafluoroborate NHFP = nitronium hexafluorophosphate... 

Sulfides react with nitronium hexafluorophosphate at -78 C to form S-nitro sulfonium ions, which isomerize to S-nitrito sulfonium ion on warai ing to -20 "C and subsequently give the corresponding sulfoxides [127aj. 

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