 The reaction then continued to give the final product of 4-hydroxyquinoline.However, Ludwig Knorr observed that under higher temperatures (approximately 140 °C) the aniline would actually attack the ester group of the β-ketoester, leading to the thermodynamically preferred β-keto acid anilide product (albeit in less than ideal yields).Continuation of this reaction using the Conrad-Limpach mechanism led to the synthesis of 2-hydroxyquinoline.