Cinnoline

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

Cinnoline

C=black, H=white, N=blue C=black, H=white, N=blue
Names
Preferred IUPAC name Cinnoline[1]
Other names Benzopyridazine
Identifiers
CAS Number	253-66-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:36617 Y
ChEMBL	ChEMBL479792 Y
ChemSpider	8853 Y
ECHA InfoCard	100.005.423
EC Number	205-964-8
Gmelin Reference	1126565
PubChem CID	9208
UNII	N5KD6I506O Y
CompTox Dashboard (EPA)	DTXSID60179943
InChI InChI=1S/C8H6N2/c1-2-4-8-7(3-1)5-6-9-10-8/h1-6H Y Key: WCZVZNOTHYJIEI-UHFFFAOYSA-N Y 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[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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:

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]}

See also

• Benzo[c]cinnoline