Q.Write reactions to bring about the following conversions :
a. Aniline into p-nitroaniline
b. Aniline into sulphanilic acid ?

Step 1. (a) Aniline to p-nitroaniline (section 13.9b). Direct nitration of unprotected aniline gives a genuine THREE-way mixture (51% para, 47% meta, 2% ortho), because the strongly acidic nitrating medium protonates -NH2 to the meta-directing -N(+)H3. To obtain p-nitroaniline cleanly as the major product, -NH2 is first protected: aniline + acetic anhydride, pyridine present, gives acetanilide + acetic acid. Acetanilide, nitrated with concentrated HNO3 + concentrated H2SO4 at 288 K, gives p-nitroacetanilide as the major product (the still-activating, but far less powerfully so, acetamido group directs cleanly to para without triggering the meta-directing protonation problem). Acid- or base-catalysed hydrolysis (H3O+/OH-) of p-nitroacetanilide then removes the acetyl protecting group, giving p-nitroaniline. …

Applying section 13.9's own worked protect-substitute-deprotect nitration scheme to part (a), and its own w …

• For part (a), nitrating unprotected aniline directly, giving the genuine 51:47:2 para:meta:ortho mixture instead of the clean major p-nitroaniline product the protection strategy specifically achieves. …