The Bernthsen acridine synthesis is the chemical reaction of a diarylamine heated with a carboxylic acid (or acid anhydride) and zinc chloride to form a 9-substituted acridine.
Using zinc chloride, one must heat the reaction to 200-270 ðC for 24hrs. The use of polyphosphoric acid will give acridine products at a lower temperature, but also with decreased yields.