sentences:  An intramolecular proton transfer is followed by an E2 mechanism, which causes a molecule of water to leave.Deprotonation at the nitrogen atom generates a Schiff base, which tautomerizes to form an enamine that gets protonated via the acid catalyst, which is commonly concentrated sulfuric acid (H2SO4).The second major step, which is also the rate-determining step, is the annulation of the molecule.