Balz–Schiemann reaction

The traditional Balz–Schiemann reaction employs HBF4 and involves isolation of the diazonium salt. Both aspects can be profitably modified. Other counterions have been used in place of tetrafluoroborates, such as hexafluorophosphates (PF6−) and hexafluoroantimonates (SbF6−) with improved yields for some substrates. The diazotization reaction can be effected with nitrosonium salts such as Nitrosonium hexafluoroantimonate|[NO]SbF6 or tert-butyl nitrite without isolation of the diazonium intermediate. The reaction has also performed under continuous flow conditions, allowing the potentially hazardous aryl diazonium salt to be prepared and immediately consumed inline without accumulating or isolating it. As a practical matter, the traditional Balz–Schiemann reaction consumes relatively expensive BF4− as a source of fluoride. An alternative methodology produces the fluoride salt of the diazonium compound. In this implementation, the diazotization is conducted with a solution of sodium nitrite in liquid hydrogen fluoride: : : ==History==

The reaction is named after the German chemists and Günther Balz. ==Examples==

4-Fluorotoluene is made in ~89% yield by Balz–Schiemann reaction on p-toluidine. This is then used as a precursor for 4-fluorobenzaldehyde, ==Additional literature==