Bernthsen acridine synthesis explained

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.^{[1] [2]}

Using zinc chloride, one must heat the reaction to 200-270 °C for 24hrs.^[3] The use of polyphosphoric acid will give acridine products at a lower temperature, but also with decreased yields.

Notes and References

1. Bernthsen, A.; Ann. 1878, 192, 1.
2. Bernthsen, A.; Ann. 1884, 224, 1.
3. Popp, F. D. J. Org. Chem. 1962, 27, 2658.