8-Hydroxyquinoline

8-Hydroxyquinoline (also known as oxine) is an organic compound derived from the heterocycle quinoline. A colorless solid, its conjugate base is a chelating agent, which is used for the quantitative determination of metal ions.

8-Hydroxyquinoline

Names
Preferred IUPAC name Quinolin-8-ol
Other names 1-Azanaphthalene-8-ol, Fennosan H 30, Hydroxybenzopyridine, Oxybenzopyridine, Oxychinolin, Oxyquinoline, Phenopyridine, Quinophenol, Oxine, 8-Quinolinol
Identifiers
CAS Number	148-24-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:48981 Y
ChEMBL	ChEMBL310555 Y
ChemSpider	1847 Y
ECHA InfoCard	100.005.193
KEGG	D05321 Y
PubChem CID	1923
UNII	5UTX5635HP Y
CompTox Dashboard (EPA)	DTXSID5020730
InChI InChI=1S/C9H7NO/c11-8-5-1-3-7-4-2-6-10-9(7)8/h1-6,11H Y Key: MCJGNVYPOGVAJF-UHFFFAOYSA-N Y InChI=1/C9H7NO/c11-8-5-1-3-7-4-2-6-10-9(7)8/h1-6,11H Key: MCJGNVYPOGVAJF-UHFFFAOYAG
SMILES C1=CC2=C(C(=C1)O)N=CC=C2
Properties
Chemical formula	C9H7NO
Molar mass	145.16 g/mol
Appearance	White crystalline powder
Density	1.034 g/cm3
Melting point	76 °C (169 °F; 349 K)
Boiling point	276 °C (529 °F; 549 K)
Pharmacology
ATC code	G01AC30 (WHO) A01AB07 (WHO) D08AH03 (WHO) R02AA14 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H317, H318, H360D, H410
Precautionary statements	P202, P273, P280, P301+P310, P302+P352, P305+P351+P338
Safety data sheet (SDS)	External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

In aqueous solution 8-hydroxyquinoline has a pK_a value of ca. 9.9^[1] It reacts with metal ions, losing the proton and forming 8-hydroxyquinolinato-chelate complexes.

Tris(8-hydroxyquinolinato)aluminium^[2]

The aluminium complex,^[3] is a common component of organic light-emitting diodes (OLEDs). Substituents on the quinoline ring affect the luminescence properties.^[4]

In its photo-induced excited-state, 8-hydroxyquinoline converts to zwitterionic isomers, in which the hydrogen atom is transferred from oxygen to nitrogen.^[5]

History

8-hydroxyquinoline was first obtained by Hugo Weidel and his student Albert Cobenzl in 1880. They decarboxylated so-called oxycinchoninic acid (from cinchonine) and characterized the resulting compound as melting at about 70°C. They identified that the hydroxy group is on the benzene ring (but not its particular place) and called the compound oxyquinoline and α-quinophenol.^[6]

In the following year more chemists found other ways to make the compound. Zdenko Hans Skraup discovered a way to synthesize substituted quinolines from substituted phenols and described three isomers of oxyquinoline, identifying the structure of 8-hydroxyquinoline.^[7] Otto Fischer [de] and his student Karl Bedall made the compound from a sulphonic acid independently at about the same time, but misidentified its structure.^[8][9]

By 1888 azo dyes were made from the compound.^[10]

In the 1920s insoluble chelates of 8-hydroxyquinoline were discovered.^[11]

Bioactivity

The complexes as well as the heterocycle itself exhibit antiseptic, disinfectant, and pesticide properties,^[12][13] functioning as a transcription inhibitor.^{[14] [dubious – discuss]} Its solution in alcohol is used in liquid bandages. It once was of interest as an anti-cancer drug.^[15]

A thiol analogue, 8-mercaptoquinoline is also known.^[16]

The roots of the invasive plant Centaurea diffusa release 8-hydroxyquinoline, which has a negative effect on plants that have not co-evolved with it.^[17]

See also

• Nitroxoline (5-nitro-8-hydroxyquinoline), an antiprotozoal drug
• PBT2
• QUPIC
• Ionophore
• Trace metal detection test

References

1. 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.
2. Cölle, M.; Dinnebier, R. E.; Brütting, W. (2002). "The structure of the blue luminescent δ-phase of tris(8-hydroxyquinoline)aluminium(III) (Alq₃)". Chemical Communications. 2002 (23): 2908–9. doi:10.1039/b209164j. PMID 12478807. S2CID 96135270.
3. Katakura, R.; Koide, Y. (2006). "Configuration-Specific Synthesis of the Facial and Meridional Isomers of Tris(8-hydroxyquinolinate)aluminum (Alq₃)". Inorganic Chemistry. 45 (15): 5730–5732. doi:10.1021/ic060594s. PMID 16841973.
4. 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 Journal. 12 (17): 4523–4535. doi:10.1002/chem.200501403. PMID 16619313.
5. 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 B. 101 (39): 7786–7793. doi:10.1021/jp971293u.
6. Weidel, H.; Cobenzl, A. (1880). "Über Derivate der Cinchoninsäure und des Chinolins". Monatshefte für Chemie und verwandte Teile anderer Wissenschaften (in German). 1 (1): 844–868. doi:10.1007/BF01517113. ISSN 1434-4475.
7. DE 14976, Skraup, Zdenko Hanus, "Verfahren zur Darstellung der Oxychinoline durch Behandlung von Mononitro- und Monamido-Phenolen mit Glycerin und Schwefelsäure", published 1881-09-10, issued 1881-02-16
8. Bedall, Karl; Fischer, Otto (1881). "Ueber Oxychinolin aus Chinolinsulfosäure". Berichte der Deutschen Chemischen Gesellschaft (in German). 14 (1): 442–443. doi:10.1002/cber.188101401101. ISSN 1099-0682.
9. Fischer, Otto (1882). "Zur Geschichte der Oxychinoline". Berichte der Deutschen Chemischen Gesellschaft (in German). 15 (2): 1979–1981. doi:10.1002/cber.188201502123. ISSN 1099-0682.
10. Journal of the Society of Dyers and Colourists. Society of Dyers and Colourists. 1888.
11. Berg, R. (1927). "Neue Wege zur Bestimmung und Trennung der Metalle mit Hilfe von o-Oxychinolin". Zeitschrift für analytische Chemie (in German). 71 (5): 171–185. doi:10.1007/BF01390921. ISSN 1618-2650.
12. Phillips, J. P. (1956). "The Reactions of 8-Quinolinol". Chemical Reviews. 56 (2): 271–297. doi:10.1021/cr50008a003.
13. "8-Hydroxyquinoline". Medical Dictionary Online. Archived from the original on 2016-10-09. Retrieved 2016-03-09.
14. "8-Hydroxyquinoline". Sigma-Aldrich. Retrieved 2022-02-15.
15. Shen, A. Y.; Wu, S. N.; Chiu, C. T. (1999). "Synthesis and Cytotoxicity Evaluation of some 8-Hydroxyquinoline Derivatives". Journal of Pharmacy and Pharmacology. 51 (5): 543–548. doi:10.1211/0022357991772826. PMID 10411213. S2CID 33085238.
16. Fleischer, H. (2005). "Structural Chemistry of Complexes of (n-1)d¹⁰ns Metal Ions with β-N-Donor Substituted Thiolate Ligands (m=0, 2)". Coordination Chemistry Reviews. 249 (7–8): 799–827. doi:10.1016/j.ccr.2004.08.024.
17. Vivanco, J.M.; Bais, H.P.; Stermitz, F.R.; Thelen, G.C.; Callaway, R.M. (2004). "Biogeographical variation in community response to root allelochemistry: novel weapons and exotic invasion". Ecology Letters. 7 (4): 285–292. Bibcode:2004EcolL...7..285V. doi:10.1111/j.1461-0248.2004.00576.x.