Bernthsen acridine synthesis

Bernthsen the reaction or Bernthsen acridine synthesis reaction is a name of the organic chemistry. It was published for the first time in 1878 by August Bernthsen ( 1885-1931 ). Is one of the first acridine synthesis by heating diphenylamines with benzonitrile. However, this is an outdated version of this reaction. Today, one uses instead of benzonitrile, preferably a carboxylic acid and zinc chloride. The acridines thus generated can be processed in quinolines on.

Mechanism

In the following, a mechanism is described, as it is postulated for this reaction:

First, it is mixed carboxylic acid 1 with zinc chloride, resulting in the elimination of zinc oxide and water, a carboxylic acid chloride 2 forms (for reasons of stoichiometry have two molecules of carboxylic acid come on a particle zinc chloride). This acid chloride reacts with diphenylamine 3 in a Friedel -Crafts acylation of the intermediate 4 to the ketone 5 zinc chloride polarizing the carbonyl group of the ketone to form the intermediate state 6 - indicated here by the dashed line. An intramolecular electrophilic substitution leads through the intermediate 7 to the tricyclic alcohol 8 with hydrochloric acid, the nitrogen atom is protonated in Figure 8 whereby the salt is 9. The gradual elimination of hydrogen chloride and water leads to the formation of the substituted acridine 10

Recycling

From the obtained in the reaction of zinc oxide and hydrogen chloride Zinc chloride can be recovered: