How would you convert Aniline to nitrobenzene?
The correct answer and explanation is:
To convert aniline (C6H5NH2) to nitrobenzene (C6H5NO2), a nitration reaction is typically used. This involves introducing a nitro group (-NO2) into the benzene ring by using a mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4), known as the nitrating mixture. Here’s the step-by-step process:
Step 1: Preparing the Nitrating Mixture
The nitrating mixture is prepared by mixing concentrated nitric acid and concentrated sulfuric acid. The sulfuric acid acts as a catalyst and helps generate the nitronium ion (NO2+), which is the electrophile required for the nitration reaction. The reaction proceeds as follows: HNO3+H2SO4→NO2++HSO4−\text{HNO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{NO}_2^+ + \text{HSO}_4^-
Step 2: Nitration of Aniline
Aniline is then treated with the nitrating mixture. The nitronium ion (NO2+) attacks the benzene ring of aniline, replacing one of the hydrogen atoms with a nitro group (-NO2). However, aniline has an amino group (-NH2), which is an activating group and makes the ring more reactive to electrophilic substitution. The amino group directs the incoming nitro group to the para position (relative to the amino group) or the ortho position on the ring.
The reaction proceeds as follows: C6H5NH2+NO2+→C6H4(NO2)NH2\text{C}_6\text{H}_5\text{NH}_2 + \text{NO}_2^+ \rightarrow \text{C}_6\text{H}_4\text{(NO}_2\text{)NH}_2
In this case, the primary product is para-nitroaniline (C6H4(NO2)NH2), but ortho-nitroaniline might also be formed.
Step 3: Oxidation of Aniline to Nitrobenzene
However, aniline’s amino group (-NH2) is also prone to being oxidized under certain conditions, especially when exposed to nitro group electrophiles, resulting in the conversion of aniline to nitrobenzene (C6H5NO2).
Final Product: Nitrobenzene
The final product is nitrobenzene, with a nitro group attached to the benzene ring in place of the amino group. This is achieved by the nitro group replacing the amino group in the reaction, typically under controlled conditions to avoid over-reaction or unwanted side products.
In summary, aniline is first nitrated using a nitrating mixture, and through careful reaction conditions, nitrobenzene is produced.