Vilsmeier–Haack reaction

The Vilsmeier -Haack reaction is a reaction name and named after the German chemist Anton Vilsmeier and Albrecht Haack. Add a personal dedication of the dissertation of Vilsmeier Haack, however, is handwritten is " inventor of this aldehyde synthesis is solely Dr. A. Vilsmeier Haack has the aldehydes prepared by Vilsmeier experimentally machined again, confirmed and summarized in this thesis. . "

The reaction involves the formylation of activated aromatic compounds with N-substituted formamides and phosphorus oxychloride ( POCl3 ). In addition to N, N-dimethylformamide is frequently the more reactive N- methylformanilide as formamide application. This reaction is one such as the Gattermann - synthesis, Gattermann - Koch synthesis or Kreutzberger formylation to a group of reactions, by reaction with derivatives of Formylchlorids which is not resistant to free in the sense of a Friedel-Crafts acylation serve for the formylation of activated aromatic compounds.

Reaction mechanism

First of all forms from the formamide and the phosphorus oxychloride, the so-called Vilsmeier reagent, a Chlorimmonium ion.

The Chlorimmonium ion reacts in an electrophilic aromatic substitution reaction with the activated aromatics. Due to the aqueous work-up of the aromatic aldehyde is released eventually. Is formylated with N- methylformanilide, we may reaction temperatures of about 70 ° C does not exceed, as the Vilsmeier reagent is subject to an otherwise Selbstformylierung.

Technical formylations by Vilsmeier - Haack are performed usually with phosgene instead of Phosphoroxichlorids.

The reaction also works in the benzylation. For example, a reaction of N, N-dimethylaniline and p- dimethylaminobenzophenone Benzoesäureanilinamid. May also be prepared via a reaction between guaiacol and N- formyl -N- methylaniline vanillin. An analogous acylation does not exist, as you can see in the chloramine- production, for example.