Mendius Reduction: Synthesis of Primary Amines
The Mendius Reduction involves the reduction of alkyl or aryl cyanides (nitriles) to Primary Amines using nascent hydrogen generated by the action of Sodium on Ethanol.
1. General Reaction
The nitrile group ($-C \equiv N$) takes up four hydrogen atoms to become a primary amine group ($-CH_2NH_2$).
Key Components:
- Substrate: Alkyl/Aryl Nitrile (Cyanide).
- Reagent: Sodium metal in absolute Ethanol ($Na/EtOH$).
- Reducing Species: Nascent Hydrogen ($[H]$).
- Product: Primary Amine ($1^\circ$).
2. Detailed Mechanism
The reaction proceeds via a dissolving metal reduction mechanism involving electron transfer and protonation.
Step 1: Electron Transfer
Sodium metal ($Na$) acts as an electron source. An electron is transferred to the electronegative Nitrogen of the cyanide group.
Step 2: Protonation (Ethanol)
Ethanol acts as the proton source. The anion abstracts a proton from ethanol to form an Imine radical.
Step 3: Further Reduction
The process repeats. The intermediate takes another electron and proton to form an Imine ($R-CH=NH$), and repeats again to finally yield the Primary Amine.
3. Examples
A. Synthesis of Ethylamine
Reduction of Methyl Cyanide (Acetonitrile).
$$ CH_3-CN + 4[H] \xrightarrow{Na/EtOH} CH_3-CH_2-NH_2 $$B. Synthesis of Benzylamine
Reduction of Phenyl Cyanide (Benzonitrile).
$$ C_6H_5-CN + 4[H] \xrightarrow{Na/EtOH} C_6H_5-CH_2-NH_2 $$4. Comparison with Isocyanides
Reduction of Isocyanides
While Mendius reduction targets nitriles to form $1^\circ$ amines, if the same reagent ($Na/EtOH$) is used on Isocyanides ($R-NC$), the product is a Secondary Methyl Amine.
$$ R-NC + 4[H] \xrightarrow{Na/EtOH} R-NH-CH_3 $$
5. Modern Alternatives
While the classic Mendius reaction uses Na/Ethanol, Lithium Aluminum Hydride ($LiAlH_4$) is a stronger modern reducing agent that performs the same transformation of Nitriles to Primary Amines.
Mendius Reduction Quiz
Test your concepts on Nitrile reduction. 10 MCQs with explanations.
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