Nitrosonium tetrafluoroborate

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Nitrosonium tetrafluoroborate
IUPAC name
Nitrosonium tetrafluoroborate
Other names
Azanylidyneoxidanium tetrafluoroborate
Nitrosium tetrafluoroborate
Nitrosyl tetrafluoroborate
Molar mass 116.81 g/mol
Appearance Colorless crystalline solid
Odor Odorless (dry air)
Acidic (moisture)
Density 2.185 g/cm3[1]
Melting point 250 (decomposes)
Boiling point Decomposes
Solubility Reacts with alcohols
Soluble in acetonitrile, conc. sulfuric acid
Sparingly soluble in benzonitrile, liq. nitrosyl chloride[2]
Insoluble in CCl4, dichloromethane, nitromethane
Vapor pressure ~0 mmHg
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
Nitronium tetrafluoroborate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Nitrosonium tetrafluoroborate, also called nitrosyl tetrafluoroborate, is a chemical compound with the chemical formula NOBF4, the nitrosonium salt of fluoroboric acid. This colourless solid is used in organic synthesis as a nitrosating agent.



The dominant property of NOBF4 is the oxidizing power and electrophilic character of the nitrosonium cation. It forms colored charge transfer complexes with hexamethylbenzene and with 18-crown-6. The latter, a deep yellow species, provides a means to dissolve NOBF4 in dichloromethane.

Nitrosonium tetrafluoroborate reacts with aliphatic azides to yield the corresponding alkyl fluorides.

With ferrocene the ferrocenium tetrafluoroborate is formed.


Nitrosonium tetrafluoroborate is a colorless crystalline solid, that react with water.


Nitrosonium tetrafluoroborate is sold by chemical suppliers.


Nitrosonium tetrafluoroborate can be prepared by adding perfectly dry hydrogen fluoride and nitrogen dioxide to boron trifluoride. Given the highly corrosive nature of the reagents used, this reaction is done in a chemical resistant polyethylene reactor. The reaction takes place is dry nitromethane, in a nitrogen atmosphere, at -20°C under continuous stirring. The yield of this reaction can reach 97%.[4] Dinitrogen pentoxide can be used instead, though the resulting yield is lower, at 89%.[5]

Another route involves reacting boron trifluoride with dry hydrogen fluoride and nitrosyl chloride, in liq. SO2, at -10°C, while stirring for 15-30 min. The final product is washed with dichloromethane. Yield is 96%.[6] One source indicates that hydrogen fluoride can be replaced with boron trioxide, and the yield will be the same.[7]

Injecting dry nitrogen dioxide in a solution of tetrafluoroboric acid will yield nitrosyl tetrafluoroborate, with nitric acid being produced as side product.[8]

Addition of dinitrogen trioxide to boron trifluoride, in nitrobenzene or liq. SO2 at 0 °C will also yield NOBF4.[9]


  • Nitrosating agent
  • Preparation of tetrafluoroborate compounds
  • Synthesis of HNIW



Nitrosonium tetrafluoroborate reacts with water, it's corrosive and toxic.


In closed airtight bottles, at low temperature, in a dry medium. Schlenks flask may also be used if available.


Should be added slowly to water to safely hydrolyze it, then neutralized with a base.


  1. Balz, G.; Mailaender, E.; Z. Anorg. Chem.; vol. 217; (1934); p. 161 - 169
  2. Yau, John; Mingos, D. Michael P.; Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999); (1997); p. 1103 - 1112
  3. Callanan, J.E.; Granville, N.W.; Green, N.H.; Staveley, L.A.K.; Weir, R.D.; White, M.A.; Journal of Chemical Physics; vol. 74; nb. 3; (1981); p. 1911 - 1915
  5. Schmeiser, M.; Elischer, S.; Zeitschrift fuer Naturforschung; vol. 7b; (1952); p. 583
  6. Kuhn, S. J.; Canadian Journal of Chemistry; vol. 45; (1967); p. 3207 - 3209
  7. Woolf, A. A.; Journal of the Chemical Society; (1950); p. 1053 - 1056
  8. Voznesenskij, S. A.; Kurskij, P. P.; Zhurnal Obshchei Khimii; vol. 8; (1938); p. 524 - 528 ;
  9. Evans, J. C.; Rinn, H. W.; Kuhn, S. J.; Olah, G. A.; Inorganic Chemistry; vol. 3; (1964); p. 857 - 861

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