Nitration and Nitrosation of Indoles

Nitration

• Nitration of indoles with different nitrating agents depends on reaction conditions due to acid sensitivity of indole nucleus.
• 3-Nitroindole is produced when indole is nitrated with benzoyl nitrate in acetonitrile or with ethyl nitrate in the presence of sodium ethoxide at low temperature.

Nitrosation

• 2-Methylindole is nitrosated with sodium nitrite in the presence of acetic acid, forming 3-oximino-2-methylindole (a form of 3-nitroso-2-methylindole).
• 3-Methylindole is nitrosated to form N-nitroso-3-methylindole.

Halogenation

• Chlorination of indole with sulfuryl chloride produces 3-chloroindole.
• Excess sulfuryl chloride reacts with 3-chloroindole to form 2,3-dichloroindole via 3,3-dichloro-3H-indole.
• Bromination of indole occurs at the position-3, forming 3-bromoindole.
• If position-3 is already substituted, bromination takes place at the position-2.

Sulfonation

• Indole is sulfonated with pyridine-sulfur trioxide complex to form indole-3-sulfonic acid.
• If position-3 is already occupied, sulfonation occurs at the position-2 via initial reversible sulfonation at position-3.

Vilsmeier-Haack Formylation

• Indole undergoes Vilsmeier-Haack formylation with N,N-dimethylformamide (DMF) in the presence of phosphorus oxychloride, forming 3-formylindole.

This quiz covers the reactions of indoles with electrophiles, specifically nitration and nitrosation, and the factors that influence the products formed. It explores the effects of different reaction conditions and nitrating agents on the outcome of these reactions.