Quinoline

Quinoline is an aromatic heterocyclic compound with a benzene ring fused to a pyridine ring. Its molecular formula is C₉H₇N.

Pyridine: Pyridine is an aromatic six-membered ring containing one nitrogen atom and five carbon atoms. One of quinoline’s fused rings has pyridine’s nitrogen-containing structure.
Electrophilic aromatic substitution: Electrophilic aromatic substitution replaces a ring hydrogen with an electrophile while restoring aromaticity. Quinoline’s benzene portion undergoes this reaction more readily than its pyridine portion.
Friedlieb Ferdinand Runge: Friedlieb Ferdinand Runge was a German chemist who isolated several compounds from coal tar. Runge reported quinoline among the substances obtained from coal tar in the nineteenth century.
Quinoline yellow: Quinoline yellow is a mixture of sulfonated quinophthalone dyes used to color foods and other products. It shows how quinoline-derived structures serve as commercial colorants.
Benzene: Benzene is a six-carbon aromatic ring with formula C₆H₆. Quinoline’s second fused ring is benzene-like.
Nucleophilic aromatic substitution: Nucleophilic aromatic substitution replaces a leaving group on an aromatic ring with a nucleophile. Quinoline’s nitrogen makes some positions on its pyridine portion susceptible to nucleophilic attack.
Coal tar: Coal tar is a complex liquid mixture produced during the destructive distillation of coal. Historical quinoline was obtained from this industrial mixture.
Chloroquine: Chloroquine is a quinoline-based antimalarial drug that also has immunomodulatory effects. Its quinoline ring is part of a medicinal scaffold developed for malaria treatment.
Aromaticity: Aromaticity is the stabilization associated with cyclic, conjugated electron systems. Aromaticity accounts for the delocalized electrons in quinoline’s fused ring system.
Quinoline N-oxide: Quinoline N-oxide is the oxidized form of quinoline in which oxygen is bonded to ring nitrogen. Oxidation at nitrogen changes the ring’s reactivity and directs subsequent substitutions.

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