Question

Give reasons  Although –NH₂ is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline

Answer 1

Nitration is usually carried out with a mixture of concentrated HNO₃ and concentrated H₂SO₄. In the presence of these acids, most of aniline gets protonated to form anilinium ion. Therefore, in presence of acids, the reaction mixture consists of aniline and anilinium ion. Nitration of aniline due to steric hindrance at ortho position, mainly gives para nitroaniline and the nitration of anilinium ion gives m-nitroaniline. In actual practice, approximately 1:1 mixture of p-nitroaniline: m-nitroaniline is obtained.

Thus, nitration of aniline gives a substantial amount of m-nitroaniline due to protonation of the amino group.