Vilsmeier–Haack reaction

The Vilsmeier–Haack reaction (also called the Vilsmeier reaction) is the chemical reaction of a substituted formamide (1) with phosphorus oxychloride and an electron-rich arene (3) to produce an aryl aldehyde or ketone (5):
 * HArZ + POCl3 + H2O → RC(=O)ArZ + HCl + H3PO4

The reaction is named after Anton Vilsmeier and.

For example, benzanilide and dimethylaniline react with phosphorus oxychloride to produce an unsymmetrical diaryl ketone. Similarly, anthracene is formylated at the 9-position. The reaction of anthracene with N-methylformanilide, also using phosphorus oxychloride, gives 9-anthracenecarboxaldehyde:


 * [[Image:Vilsmeier reaction example2.svg|thumb|650px|none|N-Methylformanilide and anthracene and phosphorus oxychloride]]

Reaction mechanism
The reaction of a substituted amide with phosphorus oxychloride gives a substituted chloroiminium ion (2), also called the Vilsmeier reagent. The initial product is an iminium ion (4b), which is hydrolyzed to the corresponding ketone or aldehyde during workup.
 * [[Image:Vilsmeier Haack Reaction Scheme.png|thumb|none|650px|The Vilsmeier–Haack reaction]]

Used in
The Vilsmeier-Haack reaction is widely used in organic chemistry for the synthesis of various compounds and is particularly useful for introducing carbonyl groups into aromatic compounds.