Schotten-Baumann Reaction: Benzoylation Mechanism | Chemca

Organic Chemistry

Schotten-Baumann Reaction: Benzoylation

By Chemca Editorial Team • Last Updated: January 2026 • 7 min read

The Schotten-Baumann Reaction describes the method of benzoylation of active hydrogen-containing compounds (like phenols, alcohols, and amines) using Benzoyl Chloride in the presence of an aqueous base (NaOH or Pyridine).

1. General Reactions

The reaction involves nucleophilic substitution at the acyl carbon.

A. With Phenols (Esterification)

$$ C_6H_5OH + C_6H_5COCl \xrightarrow{NaOH} \underbrace{C_6H_5OCOC_6H_5}_{\text{Phenyl Benzoate}} + HCl $$

B. With Amines (Amide Formation)

$$ C_6H_5NH_2 + C_6H_5COCl \xrightarrow{NaOH} \underbrace{C_6H_5NHCOC_6H_5}_{\text{Benzanilide}} + HCl $$

Conditions:

Reagent: Benzoyl Chloride ($PhCOCl$).
Base: Aqueous $NaOH$ or Pyridine.
Purpose: Synthesis of Esters and Amides (Benzoylation).

2. Detailed Mechanism

The reaction follows a Nucleophilic Acyl Substitution pathway (Addition-Elimination).

Step 1: Nucleophilic Attack

The nucleophile (e.g., Phenoxide ion $PhO^-$ generated by NaOH) attacks the carbonyl carbon of Benzoyl Chloride. The $\pi$-electrons shift to oxygen.

$$ PhO^- + Ph-C(=O)-Cl \rightarrow Ph-C(O^-)(Cl)-OPh $$

(Formation of Tetrahedral Intermediate)

Step 2: Elimination of Leaving Group

The negative charge on oxygen reforms the double bond ($C=O$), expelling the good leaving group, Chloride ion ($Cl^-$).

$$ Ph-C(O^-)(Cl)-OPh \rightarrow Ph-C(=O)-OPh + Cl^- $$

3. Role of the Base

Why is NaOH or Pyridine used?

Neutralization: The reaction produces $HCl$ as a byproduct. The base neutralizes the acid, driving the equilibrium forward (Le Chatelier's principle).
Activation: In the case of phenols, NaOH converts the phenol into the more nucleophilic Phenoxide ion ($PhO^-$).
Protection: In the case of amines, removing the $HCl$ prevents the protonation of the amine reactant (which would render it non-nucleophilic).

4. Acetylation vs. Benzoylation

Benzoylation (Schotten-Baumann) is often preferred over Acetylation (using Acetyl Chloride) for identification because:

Benzoyl derivatives are usually higher melting solids that are easier to crystallize and identify.
Benzoyl chloride reacts slower than acetyl chloride, making the reaction easier to control in aqueous conditions (it doesn't hydrolyze as instantly as acetyl chloride).

5. Summary Table

Reactant	Reagent	Product Name	Functional Group
Phenol ($PhOH$)	$PhCOCl + NaOH$	Phenyl Benzoate	Ester
Aniline ($PhNH_2$)	$PhCOCl + NaOH$	Benzanilide	Amide
Ethanol ($EtOH$)	$PhCOCl + Pyridine$	Ethyl Benzoate	Ester

Schotten-Baumann Quiz

Test your concepts on Benzoylation. 10 MCQs with explanations.

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