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The Vilsmeier-Haack reaction or Vilsmeier reaction is an organic reaction between a substituted amide and an activated arene in the presence of phosphorus oxychloride. The initial reaction produces an imine, which is hydrolyzed to the corresponding aromatic ketone or aldehyde. 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.
Reaction mechanism
The reaction of the amide with phosphorus oxychloride produces an electrophilic iminium cation. The subsequent electrophilic aromatic substitution produces an imine intermediate, which is easily hydrolyzed to give the desired aryl ketone or aryl aldehyde.
Applications
One recent application of this reaction involved a new synthetic route to tris(4-formylphenyl)amine from triphenylamine which by known procedures only resulted in a modest chemical yield of 16%. It was found that this low yield was caused by deactivation of the remaining benzene ring by the imine groups on the other two phenyl groups in the third formylation step. The procudure was modified by taking the reaction to di-imine compound followed by hydrolysis to the di-formyl compound and then (with final position reactived) a separate formylation to the tri substituted compound.
References
- Vilsmeier, A.; Haack, A. Ber. 1937, 60, 119.
- Formylation of dimethylaniline. Organic Syntheses, Coll. Vol. 4, p.331; Vol. 33, p.27. (Article)
- Vilsmeyer-Haack reaction of benzanilide and dimethylaniline. Organic Syntheses, Coll. Vol. 1, p.217; Vol. 7, p.24. (Article)
- Formylation of anthracene. Organic Syntheses, Coll. Vol. 3, p.98; Vol. 20, p.11. (Article)
- Practical and Efficient Synthesis of Tris(4-formylphenyl)amine, a Key Building Block in Materials Chemistry Thomas Mallegol, Said Gmouh, Mohamed Aït Amer Meziane, Mireille Blanchard-Desce, Olivier Mongin Synthesis 2005, 1771-1774. (Abstract)
See also
"Vilsmeier-Haack reaction"