Benzenediazonium tetrafluoroborate
Organic compound containing an –N≡N+ function
From Wikipedia, the free encyclopedia
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,[2] which are widely used in organic chemistry.
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| Names | |
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| IUPAC name
Benzenediazonium tetrafluoroborate | |
| Other names
Phenyldiazonium tetrafluoroborate | |
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| Properties | |
| C6H5BF4N2 | |
| Molar mass | 191.92 g·mol−1 |
| Appearance | colorless crystals |
| Density | 1.565 g/cm3 |
| Melting point | 77 °C (171 °F; 350 K)[1] |
| Boiling point | Decomposes at 91 °C (196 °F; 364 K)[1] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis
Diazotization of aniline with nitrous acid in the presence of hydrochloric acid gives phenyldiazonium chloride:
- C6H5NH2 + HNO2 + HCl → [C6H5N2]Cl + 2 H2O
The required nitrous acid can be generated in situ by combining sodium nitrite and hydrochloric acid.[3] The tetrafluoroborate salt of phenyl diazonium can be obtained from benzenediazonium chloride by salt metathesis using tetrafluoroboric acid.
- [C6H5N2]Cl + HBF4 → [C6H5N2]BF4 + HCl
The tetrafluoroborate is more stable than the chloride.[4]
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.
Reaction with aniline gives 1,3-diphenyltriazene.[5]
The structure of the salt has been verified by X-ray crystallography. The N-N bond distance is 1.083(3) Å.[6]
Safety
While tetrafluoroborate salts are typically less sensitive than chlorides, all aryldiazonium salts should be assumed to pose a risk of explosion "unless proved otherwise".[7]
Benzenediazonium tetrafluoroborate has been described as shock-insensitive,[8][9] and, when dry, decomposes smoothly upon heating.[4] It is less sensitive than benzenediazonium chloride, which is liable to detonate upon exposure to heat, friction, or shock.[10]