Chemistry · Amines · NEET
Acylation replaces a hydrogen of the N-H bond with an acyl group. A tertiary amine (R3N) has NO N-H hydrogen left on nitrogen, so there is nothing to replace and no amide can form. Only 1deg amines (which have 2 N-H bonds) and 2deg amines (1 N-H) form amides. This is a favourite NEET one-liner.
An AMIDE. A 1deg amine RNH2 gives R-NH-CO-R' (an N-substituted amide). A 2deg amine R2NH gives R2N-CO-R' (an N,N-disubstituted amide). The rule: the acyl group R'-CO- attaches to nitrogen and one N-H hydrogen leaves as part of HCl (from acid chloride) or as a carboxylic acid/alcohol (from anhydride/ester).
Benzoylation is just acylation using benzoyl chloride C6H5COCl as the acylating agent, so the group added is the benzoyl group C6H5CO-. Aniline + C6H5COCl gives C6H5NHCOC6H5 (N-phenylbenzamide, also called benzanilide). Acylation is the general name; benzoylation and acetylation (using CH3COCl or acetic anhydride) are specific cases.
When an acid chloride reacts, HCl is released. HCl is acidic and would protonate the basic amine, tying up its lone pair and stopping the reaction. A base like pyridine (or NaOH in the Schotten-Baumann method) neutralises the HCl as it forms. This shifts the reversible reaction to the right and drives it to completion. NCERT states this directly.
Yes. Aniline + acetic anhydride (or CH3COCl) gives acetanilide (C6H5NHCOCH3), an acetylation. NEET links this to protecting the -NH2 group before nitration or bromination, because the acetyl group lowers the ring's high reactivity so a single para product forms. Acid hydrolysis then removes the acetyl group to get aniline back.
Identify the reactions which give aniline as the major product. (A) C6H5CN with LiAlH4; (B) C6H5CONH2 with KOH, Br2; (C) C6H5NO2 with NaBH4; (D) C6H5NHCOCH3 with HCl, H2O, heat. Choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Acid chlorides (R-CO-Cl), acid anhydrides (R-CO-O-CO-R), and esters (R-CO-OR'). Acid chlorides are the most reactive. Benzoyl chloride (C6H5COCl) is used for benzoylation.
It is benzoylation (or acylation) of an amine or alcohol using benzoyl chloride in the presence of aqueous NaOH. The NaOH neutralises the HCl formed and pushes the reaction to completion.
It decreases it. The nitrogen lone pair now shares into the C=O of the amide by resonance, so it is far less available to accept a proton. Amides are much weaker bases than amines.
Yes. Aniline is a 1deg aromatic amine with N-H, so it is readily acetylated to acetanilide or benzoylated to benzanilide. This is used to protect the -NH2 group before electrophilic substitution.
It protects the reactive -NH2 group. The acyl group lowers the ring's over-reactivity, letting you do controlled nitration or halogenation, and it is easily removed later by acid or base hydrolysis to restore the amine.
