8-Hydroxyquinoline is an organic compound with the formula C9H7NO. It is a derivative of the heterocyclequinoline by placement of an OH group on carbon number 8. This light yellow compound is widely used commercially, although under a variety of names.
8-Hydroxyquinoline is a monoprotic bidentate chelating agent. Related ligands are the Schiff bases derived from salicylaldehyde, such as salicylaldoxime, salen and salicylaldehyde isonicotinoylhydrazone (SIH). In neutral solution, the hydroxyl is in the protonated form (pKa=9.89) and the nitrogen is not protonated (pKa=5.13). However, an excited-state zwitterionic isomer exists in which H+ is transferred from the oxygen (giving an oxygen anion) to the nitrogen (giving a protonated nitrogen cation).
^Albert, A.; Phillips, J. N. (1956). "264. Ionization Constants of Heterocyclic Substances. Part II. Hydroxy-Derivatives of Nitrogenous Six-Membered Ring-Compounds". Journal of the Chemical Society (Resumed)1956: 1294–1304. doi:10.1039/JR9560001294.
^Bardez, E.; Devol, I.; Larrey, B.; Valeur, B. (1997). "Excited-State Processes in 8-Hydroxyquinoline: Photoinduced Tautomerization and Solvation Effects". The Journal of Physical Chemistry B101 (39): 7786–7793. doi:10.1021/jp971293u.
^Phillips, J. P. (1956). "The Reactions of 8-Quinolinol". Chemical Reviews56 (2): 271–297. doi:10.1021/cr50008a003.
^Shen, A. Y.; Wu, S. N.; Chiu, C. T. (1999). "Synthesis and Cytotoxicity Evaluation of some 8-Hydroxyquinoline Derivatives". Journal of Pharmacy and Pharmacology51 (5): 543–548. doi:10.1211/0022357991772826. PMID10411213.
^Katakura, R.; Koide, Y. (2006). "Configuration-Specific Synthesis of the Facial and Meridional Isomers of Tris(8-hydroxyquinolinate)aluminum (Alq3)". Inorganic Chemistry45 (15): 5730–5732. doi:10.1021/ic060594s.
^Montes, V. A.; Pohl, R.; Shinar, J.; Anzenbacher, P. Jr. (2006). "Effective Manipulation of the Electronic Effects and Its Influence on the Emission of 5-Substituted Tris(8-quinolinolate) Aluminum(III) Complexes". Chemistry - A European Journal12 (17): 4523–4535. doi:10.1002/chem.200501403.