On nitration of quinoline, Nitration occur which position at quinoline...
Nitration of Quinoline
The nitration of quinoline involves the substitution of a nitro group (-NO2) onto the quinoline molecule. Nitration is a common reaction in organic chemistry and is often used to introduce functional groups onto aromatic compounds. In the case of quinoline, the major product of nitration is formed by the substitution of the nitro group at the 5-position of the quinoline ring.
Explanation:
1. Structure of Quinoline
Quinoline is a heterocyclic aromatic compound consisting of a benzene ring fused to a pyridine ring. It has a nitrogen atom in the 1-position and a double bond between the 2- and 3-carbon atoms. The numbering of the carbon atoms in the quinoline ring starts from the nitrogen atom.
2. Nitration Reaction
During the nitration reaction, a mixture of nitric acid (HNO3) and sulfuric acid (H2SO4) is used as the nitrating agent. The sulfuric acid serves as a catalyst and also helps in the formation of the nitronium ion (NO2+), which is the electrophile responsible for the substitution reaction.
3. Electrophilic Aromatic Substitution
The nitronium ion (NO2+) acts as an electrophile and attacks the electron-rich aromatic ring of quinoline. The reaction proceeds through an electrophilic aromatic substitution mechanism. The nitrogen atom in the quinoline ring can donate electron density to the ring, making the carbon atoms in the 5-position more nucleophilic compared to the other positions.
4. Attack at the 5-Position
Due to the greater nucleophilicity of the 5-position carbon atom, the nitronium ion preferentially attacks this position. The electrophilic attack leads to the substitution of a nitro group (-NO2) at the 5-position of the quinoline ring. This substitution reaction is regioselective, meaning that it occurs selectively at a specific position.
5. Major Product Formation
As a result of the preferential attack at the 5-position, the major product of the nitration of quinoline is formed by the substitution of the nitro group at this position. The other positions on the quinoline ring are less nucleophilic and hence less reactive towards electrophilic attack.
Overall, the nitration of quinoline produces the major product with a nitro group substituted at the 5-position of the quinoline ring. This regioselectivity can be attributed to the electronic effects of the nitrogen atom in the quinoline ring, which enhances the nucleophilicity of the 5-position carbon atom.