Vilsmeier–Haack reaction

Vilsmeier-Haack reaction
Named after	Anton Vilsmeier Albrecht Haack
Reaction type	Substitution reaction
Identifiers
Organic Chemistry Portal	vilsmeier-reaction
RSC ontology ID	RXNO:0000055

The Vilsmeier–Haack reaction (also called the Vilsmeier reaction) is the chemical reaction of a substituted amide (1) with phosphorus oxychloride and an electron-rich arene (3) to produce an aryl aldehyde or ketone (5). The reaction is named after Anton Vilsmeier and Albrecht Haack. 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 aromatic ketone or aldehyde during workup.

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

The reaction of the amide with phosphorus oxychloride produces an electrophilic iminium cation. The subsequent electrophilic aromatic substitution produces an iminium ion intermediate, which is hydrolyzed to give the desired aryl ketone or aryl aldehyde.

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