Ozone fading of phenolphthalein and aurin

The reactions of phenolphthalein, which exists as a lactone-quinonoid tautomeric mixture in solution, and aurin with ozone have been examined. The reactivity of the lactone tautomer of phenolphthalein with ozone was found to be low and the ozone attacks the aromatic ring. In the case of the quinonoid tautomer the ozone readily reacts with the carbon skeleton. In the case of aurin ozone also attacks the carbon skeleton.