 The Conrad-Limpach reaction mechanism also involves multiple keto-enol tautomerizations, all of which are catalyzed through the use of a strong acid, often HCl or H2SO4.With much of the literature on the synthesis of quinolines, there is some discrepancy on whether a substituted 4-hydroxyquinoline or a substituted 4-quinolone is the final product of the Conrad–Limpach synthesis.Although the reaction product is often shown as a hydroxyquinoline (the enol form), it is believed that the quinolone (keto form) predominates.