on the reaction of phthalaldehyde (OPA) with primary amines. In this contribution, aminoethanol (=kolamin) as a nitrogen‐containing nucleophile was used for the investigation of its reaction mechanism with OPA performed in basic aqueous buffered media (pH 9.5), where an influence of hydration or solvation is expected, and in anhydrous acetonitrile. Depending on the detailed reactionconditions, seven