Cinnoline

Cinnoline
C=black, H=white, N=blue	C=black, H=white, N=blue
Names
	Preferred IUPAC name Cinnoline
	Other names Benzopyridazine
Identifiers
CAS Number	253-66-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:36617 ;
ChEMBL	ChEMBL479792 ;
ChemSpider	8853 ;
ECHA InfoCard	100.005.423
PubChem CID	9208;
UNII	N5KD6I506O ;
CompTox Dashboard (EPA)	DTXSID60179943 ;
	InChI InChI=1S/C8H6N2/c1-2-4-8-7(3-1)5-6-9-10-8/h1-6H Key: WCZVZNOTHYJIEI-UHFFFAOYSA-N ; InChI=1/C8H6N2/c1-2-4-8-7(3-1)5-6-9-10-8/h1-6H Key: WCZVZNOTHYJIEI-UHFFFAOYAA;
	SMILES n1nccc2ccccc12;
Properties
Chemical formula	C8H6N2
Molar mass	130.150 g·mol−1
Melting point	39 °C (102 °F; 312 K)
Acidity (pKa)	2.64
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Cinnoline is an aromatic heterocyclic compound with the formula C₈H₆N₂. It is isomeric with other naphthyridines including quinoxaline, phthalazine and quinazoline.

Properties

The free base can be obtained as an oil by treatment of the hydrochloride with base. It co-crystallizes with one molecule of ether as white silky needles, (m.p. 24–25 °C) upon cooling ethereal solutions. The free base melts at 39 °C. It has a taste resembling that of chloral hydrate and leaves a sharp irritation for some time.

Discovery and synthesis

The compound was first obtained in impure form by cyclization of the alkyne o-C₆H₄(N₂Cl)C≡CCO₂H in water to give 4-hydroxycinnoline-3-carboxylic acid. This material could be decarboxylated and the hydroxyl group reductively removed to give the parent heterocycle. This reaction is called the Richter cinnoline synthesis.^[3]

Improved methods exist for its synthesis. It can be prepared by dehydrogenation of dihydrocinnoline with freshly precipitated mercuric oxide. It can be isolated as the hydrochloride.^[4]

Cinnolines are cinnoline derivatives. A classic organic reaction for synthesizing cinnolines is the Widman–Stoermer synthesis,^[5] a ring-closing reaction of an α-vinyl- aniline with hydrochloric acid and sodium nitrite:

The sodium nitrite is first converted to nitrous acid and then dinitrogen trioxide. The latter electrophilically attacks the amine nitrogen to form a nitrosamine and then diazonium salt. Finally the diazonium closes a ring into the vinyl group. — Widman–Stoermer reaction

A conceptually related reaction is the Bamberger triazine synthesis towards triazines.

Another cinnoline method is the Borsche cinnoline synthesis.

Safety

Cinnoline is toxic.^{[citation needed]}

References

^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 212. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
^ Brown, H.C., et al., in Baude, E.A. and Nachod, F.C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
^ Victor von Richter (1883). "Über Cinnolinderivate". Chemische Berichte. 16: 677–683. doi:10.1002/cber.188301601154.
^ Parrick, J.; Shaw, C. J. G.; Mehta, L. K. (2000). "Pyridazines, cinnolines, benzocinnolines and phthalazines". Rodd's Chemistry of Carbon Compounds. Vol. 4 (2nd ed.). pp. 1–69.
^ Bradford P. Mundy; Michael G. Ellerd; Frank G. Jr. Favaloro (2005). Name Reactions and Reagents in Organic Synthesis. ISBN 0-471-22854-0.

[1] International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 212. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.

[2] Brown, H.C., et al., in Baude, E.A. and Nachod, F.C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.

[3] Victor von Richter (1883). "Über Cinnolinderivate". Chemische Berichte. 16: 677–683. doi:10.1002/cber.188301601154.

[4] Parrick, J.; Shaw, C. J. G.; Mehta, L. K. (2000). "Pyridazines, cinnolines, benzocinnolines and phthalazines". Rodd's Chemistry of Carbon Compounds. Vol. 4 (2nd ed.). pp. 1–69.

[5] Bradford P. Mundy; Michael G. Ellerd; Frank G. Jr. Favaloro (2005). Name Reactions and Reagents in Organic Synthesis. ISBN 0-471-22854-0.

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Properties

Discovery and synthesis

Safety

See also

References