Cinnoline

Names

Preferred IUPAC name

Cinnoline

Other names

Benzopyridazine

Identifiers

CAS Number

253-66-7^Y

3D model (JSmol)

Interactive image

ChEBI

CHEBI:36617^Y

ChemSpider

8853^Y

ECHA InfoCard

100.005.423

PubChem CID

9208

UNII

N5KD6I506O^Y

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

130.15 g·mol⁻¹

Melting point

39 °C (102 °F; 312 K)

Acidity (pK_a)

2.64

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

(what is ^YN ?)

Infobox references

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

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. Cinnoline derivatives are obtained from oxycinnoline carboxylic acid, which is formed by digesting orthophenyl propiolic acid diazo chloride with water. Oxycinnoline carboxylic acid on heating gives oxycinnoline, melting at 225 °C, which with phosphorus pentachloride gives chlorcinnoline. This substance is reduced by iron filings and sulfuric acid to dihydrocinnoline.

The compound was first obtained in impure form by cyclization of the alkyne o-C₆H₄(NH₂)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 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.

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

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