Benzenediazonium tetrafluoroborate is an organic compound with the formula [C<sub>6</sub>H<sub>5</sub>N<sub>2</sub>]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.
Diazotization of aniline in the presence of hydrochloric acid:
C6H5NH2 + HNO2 + HCl → [C<sub>6</sub>H<sub>5</sub>N<sub>2</sub>]Cl + 2 H2OThe tetrafluoroborate can be obtained from crude benzenediazonium chloride by salt metathesis using tetrafluoroboric acid.
[C<sub>6</sub>H<sub>5</sub>N<sub>2</sub>]Cl + HBF4 → [C<sub>6</sub>H<sub>5</sub>N<sub>2</sub>]BF4 + HCl
The tetrafluoroborate is more stable than the chloride.[2]
See 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 + N2These 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]
Whereas the chloride salt is explosive, the tetrafluoroborate is readily isolated.