Benzenediazonium tetrafluoroborate

Benzenediazonium tetrafluoroborate
Names
	IUPAC name Benzenediazonium tetrafluoroborate
	Other names Phenyldiazonium tetrafluoroborate
Identifiers
CAS Number	369-57-3;
PubChem CID	5284485;
Properties
Chemical formula	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). (what is ?) 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

^ March, J. (1992). Advanced Organic Chemistry (4th ed.). New York: J. Wiley and Sons. ISBN 0-471-60180-2.
^ Flood, D. T. (1933). "Fluorobenzene". Org. Synth. 13: 46. doi:10.15227/orgsyn.013.0046.
^ Hartman, W. W.; Dickey, J. B. (1934). "Diazoaminobenzene". Organic Syntheses. 14: 24. doi:10.15227/orgsyn.014.0024.
^ 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.
^ Nesmajanow, A. N. (1932). "β-Naphthylmercuric chloride". Organic Syntheses. 12: 54; Collected Volumes, vol. 2, p. 432.

[1] March, J. (1992). Advanced Organic Chemistry (4th ed.). New York: J. Wiley and Sons. ISBN 0-471-60180-2.

[OS-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; Collected Volumes, vol. 2, p. 432.

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