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Benzenediazonium tetrafluoroborate
Organic compound containing an –N≡N+ function

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, which are widely used in organic chemistry.

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Synthesis

Diazotization of aniline:

C6H5NH2 + HNO2 (from NaNO2 and HCl) + 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

Main article: Diazonium compound

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.

Reaction 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. 0-471-60180-2 ↩

  2. Flood, D. T. (1933). "Fluorobenzene". Org. Synth. 13: 46. doi:10.15227/orgsyn.013.0046. /wiki/Doi_(identifier) ↩

  3. Hartman, W. W.; Dickey, J. B. (1934). "Diazoaminobenzene". Organic Syntheses. 14: 24. doi:10.15227/orgsyn.014.0024. /wiki/Doi_(identifier) ↩

  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. https://doi.org/10.1139%2Fv82-407 ↩

  5. Nesmajanow, A. N. (1932). "β-Naphthylmercuric chloride". Organic Syntheses. 12: 54; Collected Volumes, vol. 2, p. 432. http://www.orgsyn.org/demo.aspx?prep=cv2p0432 ↩