Q.Write chemical reaction of aniline with benzoyl chloride and write the name of the product obtained.

Concept: Nucleophilic substitution on an acyl chloride (benzoylation).

Reasoning:

1. Aniline ($\ce{C6H5NH2}$) acts as a nucleophile via its lone pair on nitrogen.
2. Benzoyl chloride ($\ce{C6H5COCl}$) has an electrophilic carbonyl carbon, which is attacked by aniline’s nitrogen. …

The Concept: Why This Reaction Works

Aniline ($\ce{C6H5NH2}$) is a primary aromatic amine. Its nitrogen atom carries a lone pair of electrons, making it a good nucleophile. Benzoyl chloride ($\ce{C6H5COCl}$) is an acyl chloride — one of the most reactive carboxylic acid derivatives. The carbonyl carbon in benzoyl chloride is strongly electrophilic because:

• The electronegative oxygen pulls electron density away via the $\ce{C=O}$ double bond.
• The chlorine atom is both electron-withdrawing (inductive effect) and a good leaving group.

So when aniline meets benzoyl chloride, the nucleophilic nitrogen attacks the electrophilic carbonyl carbon. This is a classic nucleophilic acyl substitution reaction — not a simple SN1 or SN2, but a two-step addition-elimination that is characteristic of acyl compounds.

Step-by-Step Mechanism

1. Nucleophilic attack

   The lone pair on the nitrogen of aniline attacks the electrophilic carbonyl carbon of benzoyl chloride. This forms a tetrahedral intermediate where the oxygen now bears a negative charge (an alkoxide ion).

2. Elimination of the leaving group

   The tetrahedral intermediate collapses. The $\ce{C=O}$ bond reforms, and the chlorine atom leaves as chloride ion ($\ce{Cl-}$). The chloride ion then abstracts a proton from the positively charged nitrogen (which had become $\ce{-NH2+}$ after attack), regenerating the neutral amide.

3. Overall reaction

   The net result is that the $\ce{-Cl}$ group of benzoyl chloride is replaced by the $\ce{-NH-C6H5}$ group from aniline. The byproduct is hydrogen chloride (HCl). …

Method: Nucleophilic Acyl Substitution (Addition-Elimination Mechanism)

This reaction follows the standard mechanism for nucleophilic substitution at an acyl carbon (carbonyl group).

Steps of the Mechanism

1. Nucleophilic Attack

   The lone pair on the nitrogen atom of aniline ($\ce{C6H5NH2}$) attacks the electrophilic carbonyl carbon of benzoyl chloride ($\ce{C6H5COCl}$).

   • This forms a tetrahedral intermediate.

2. Elimination of Leaving Group

   The tetrahedral intermediate collapses, expelling the chloride ion ($\ce{Cl-}$) as a leaving group.

   • The carbonyl group is reformed.

3. Deprotonation

   The intermediate loses a proton (from the nitrogen) to give the final neutral product.

Chemical Reaction …

Here are the common mistakes students make when writing the reaction of aniline with benzoyl chloride, along with how to avoid each one.

1. Writing the wrong product (confusing with other acylations)

The Mistake:

Students often write the product as a secondary amide (like $C_6H_5NHCOCH_3$) or confuse it with acetylation (using acetyl chloride). They forget that benzoyl chloride has a benzene ring attached to the carbonyl group.

How to Avoid:

• Always identify the acyl group: benzoyl chloride = $C_6H_5COCl$.
• The product is N-phenylbenzamide (or benzanilide).
• Write the structure clearly:

Key result: The product is N-phenylbenzamide (common name: benzanilide).

2. Forgetting the role of a base (pyridine or NaOH)

The Mistake:

Students write the reaction without a base, showing only aniline + benzoyl chloride → product + HCl. They don’t realise that the HCl produced will protonate aniline (a base) and stop the reaction.

How to Avoid:

• Remember: aniline is a weak base; HCl will form anilinium chloride ($C_6H_5NH_3^+Cl^-$), which is unreactive.
• Always include a base (usually pyridine or dilute NaOH) to neutralise the HCl.
• Write the balanced equation with the base shown.

3. Naming the product incorrectly

The Mistake:

Students give names like “benzoyl aniline” or “phenyl benzamide” — these are not IUPAC or common names accepted in exams.

How to Avoid:

• Learn the correct names:
  • IUPAC: N-phenylbenzamide
  • Common name: Benzanilide
• The “N-” prefix is crucial because the benzoyl group is attached to the nitrogen of aniline.

4. Writing the wrong mechanism (SN1 vs SN2 confusion)

The Mistake:

Students treat this as an SN1 or SN2 reaction on the carbon of benzoyl chloride. In reality, it’s a nucleophilic acyl substitution — the mechanism is different (addition-elimination via a tetrahedral intermediate).

How to Avoid:

• Understand that the carbonyl carbon is electrophilic, not the carbon attached to Cl.
• The nucleophile (aniline) attacks the carbonyl carbon, not the C–Cl bond.
• Draw the mechanism step-by-step:
  1. Nucleophilic attack by aniline’s lone pair on $C=O$
  2. Tetrahedral intermediate forms
  3. Elimination of $Cl^-$
  4. Deprotonation gives the amide

5. Ignoring the effect of substituents on reactivity

The Mistake: …