The azo-coupling reaction between 8-aminoquinoline and 3,5-dimethoxyphenol produces 2,6-dimethoxycyclohexa-2,5-diene-1,4-dione 1-[2-(quinolin-8-yl)hydrazone], C17H15N3O3. Crystallization from methanol and strong alkaline solutions produced nonsolvated and solvated crystals, respectively. The crystal structure analysis and 1H NMR spectroscopy studies revealed that the compound exists only as the hydrazone form. A UV-Vis spectroscopic titration study revealed that the hydrazone compound has a relatively high pKa value of 10.0.
Keywords: acidity study; crystal structure; hydrazone compound; quinoline; tautomerism.