Benzenediazonium tetrafluoroborate
Benzenediazonium tetrafluoroborate is an organic compound with the formula 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.
Synthesis
of aniline with nitrous acid in the presence of hydrochloric acid gives phenyldiazonium chloride:The required nitrous acid can be generated in situ by combining sodium nitrite and hydrochloric acid.
The tetrafluoroborate salt of phenyl diazonium can be obtained from benzenediazonium chloride by salt metathesis using tetrafluoroboric acid.
The tetrafluoroborate is more stable than the chloride.
Properties
The diazo group can be replaced by many other groups, usually anions, giving a variety of substituted phenyl derivatives: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.
The structure of the salt has been verified by X-ray crystallography. The N-N bond distance is 1.083 Å.