His habilitation followed three years later in 1885 with a thesis titled Über die Bildung von Kohlenstoff-Stickstoff-Ringen durch Ein-wirkung von Amin-und Hydrazinbasen auf Acetessigester und seine Derivate ("On the formation of carbon-nitrogen rings through the action of amine and hydrazine bases on acetoacetate and its derivatives"). In that time, during his search for quinine related compounds, Knorr discovered the unmethylated Phenazone. As another quinine-related compound kairin showed analgesic and antipyretic properties, Knorr and Fisher asked Wilhelm Filehne at the Hoechst company to check the unmethylated and the methylated phenazone for its pharmacological properties.