Benzenediazonium tetrafluoroborate
Names
IUPAC name
Benzenediazonium tetrafluoroborate
Other names
Phenyldiazonium tetrafluoroborate
Identifiers
ECHA InfoCard 100.002.584
Properties
C6H5BF4N2
Molar mass 191.92 g·mol−1
Appearance colorless crystals
Density 1.565 g/cm3
Melting point decomposes
Boiling point decomposes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzenediazonium tetrafluoroborate is an organic compound with the formula [C6H5N2]BF4. It is a salt of a diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solvents. It is the parent member of the aryldiazonium compounds,[1] which are widely used in organic chemistry.

Synthesis

Diazotization of aniline in the presence of hydrochloric acid:

C6H5NH2 + HNO2 + HCl → [C6H5N2]Cl + 2 H2O

The tetrafluoroborate can be obtained from crude benzenediazonium chloride by salt metathesis using tetrafluoroboric acid.

[C6H5N2]Cl + HBF4 → [C6H5N2]BF4 + HCl

The tetrafluoroborate is more stable than the chloride.[2]

Properties

The diazo group (N2) can be replaced by many other groups, usually anions, giving a variety of substituted phenyl derivatives:

C6H5N2+ + Nu− → C6H5Nu + N2

These transformations are associated with many named reactions including the Schiemann reaction, Sandmeyer reaction, and Gomberg-Bachmann reaction. A wide range of groups that can be used to replace N2 including halide, SH−, CO2H−, OH−. Of considerable practical value in the dye industry are the diazo coupling reactions.

The reaction of phenyldiazonium salts with aniline gives 1,3-diphenyltriazene.[3]

The structure of the salt has been verified by X-ray crystallography. The N-N bond distance is 1.083(3) Å.[4]

Safety

Whereas the chloride salt is explosive,[5] the tetrafluoroborate is readily isolated.

References

  1. ↑ March, J. (1992). Advanced Organic Chemistry (4th ed.). New York: J. Wiley and Sons. ISBN 0-471-60180-2.
  2. ↑ Flood, D. T. (1933). "Fluorobenzene". Org. Synth. 13: 46. doi:10.15227/orgsyn.013.0046.
  3. ↑ Hartman, W. W.; Dickey, J. B. (1934). "Diazoaminobenzene". Organic Syntheses. 14: 24. doi:10.15227/orgsyn.014.0024.
  4. ↑ Cygler, Miroslaw; Przybylska, Maria; Elofson, Richard Macleod (1982). "The Crystal Structure of Benzenediazonium Tetrafluoroborate, C6H5N2+•BF4−1". Canadian Journal of Chemistry. 60 (22): 2852–2855. doi:10.1139/v82-407.
  5. ↑ Nesmajanow, A. N. (1932). "β-Naphthylmercuric chloride". Organic Syntheses. 12: 54.; Collective Volume, vol. 2, p. 432
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