Friedländer prepared quinoline in 1882 by the condensation of o-aminobenzaldehyde with acetaldehyde in the presence of sodium hydroxide. This type of reaction has since been extensively explored and, in its most general form, can be defined as an acid- or base-catalyzed condensation followed by a cyclodehydration between an o-amino-substituted aromatic aldehyde, ketone, or derivative thereof with an appropriately substituted aldehyde, ketone, or other carbonyl compound containing a reactive α-methylene group. Some quinolines can also be prepared simply by heating a mixture of the reactants with or without a solvent.