Synthesis and Reactions of Isoquinoline

Isoquinoline consists of a benzene ring fused to the β ,γ positions of a pyridine ring. It is isomeric with quinoline.

Synthesis of Isoquinoline

Synthesis of Isoquinoline from Cinnamaldehyde

Condensation of cinnamaldehyde with hydroxylamine to form the corresponding oxime which is heated with phosphorous pentaoxide to yield isoquinoline.

Bischler-Napieralski Synthesis of Isoquinoline

2-phenylethylamine is first treated with ormyl chloride in the presence of a base to form N-formyl-2-phenylethylamine. This amide is then heated with P2O5 in pyridine to give 3,4-dihydroisoquinoline which on oxidation with palladium or selenium yields isoquinoline.

Physical Properties of Isoquinoline

Isoquinoline is a colorless solid, Its boiling Point is 243°C and Melting point is 26°C, and has benzaldehyde-like smell. It is a volatile steam, sparingly soluble in water and is soluble in organic solvents.It turns yellow on normal storage.

Chemical Properties of Isoqinoline/Reactions of Isoquinoline

Isoquinoline is stronger base than quinoline and forms stable salts with acids. Isoquinoline gives almost same reactions as Quinoline. Electrophilic substitution reaction takes place at C-5 and C-8. On oxidation with KMnO₄ gives pyridine-3,4-dicarboxylic acid.