Reduction of Nitriles
Formation of primary amines by the reduction of nitriles using lithium aluminium hydride (LiAlH4) or catalytic hydrogenation.
What is Reduction of Nitriles?
An organic compound containing a cyano group (-C≡N).
Key formula / rule: Reduction of Nitrile
Key points
- To understand the conversion of nitriles to primary amines.
- To identify the appropriate reagents for the reduction of nitriles.
- To explain the mechanism of nitrile reduction (briefly).
- To apply this reaction in the synthesis of primary amines.
Common exam trap
Using water or protic solvents with LiAlH4, which will quench the reagent and potentially cause an explosion.
Definitions
- Term
Nitrile
- Meaning
An organic compound containing a cyano group (-C≡N).
- Term
Primary Amine
- Meaning
An organic compound in which the nitrogen atom is bonded to one alkyl or aryl group and two hydrogen atoms (-NH2).
- Term
Lithium Aluminium Hydride (LiAlH4)
- Meaning
A powerful reducing agent used in organic synthesis to reduce various functional groups, including nitriles, esters, and carboxylic acids.
- Term
Catalytic Hydrogenation
- Meaning
A chemical reaction in which hydrogen gas is added to a substrate in the presence of a catalyst, typically a transition metal.
Learning objectives
To understand the conversion of nitriles to primary amines.
To identify the appropriate reagents for the reduction of nitriles.
To explain the mechanism of nitrile reduction (briefly).
To apply this reaction in the synthesis of primary amines.
Formulae
- Name
Reduction of Nitrile
- Note
Followed by further reduction to R-CH2-NH2
- Expression
R-C≡N + 2H₂ → R-CH=NH (intermediate imine)
- Name
Reduction with LiAlH4
- Note
Requires anhydrous solvent like dry ether or THF
- Expression
R-C≡N + LiAlH₄ → R-CH₂-NH₂
- Name
Catalytic Hydrogenation
- Note
Often performed under pressure
- Expression
R-C≡N + 2H₂ (excess) --(Ni/Pt/Pd)-→ R-CH₂-NH₂
Prerequisites
Understanding of functional groups (nitriles, amines).
Knowledge of oxidation states and redox reactions.
Familiarity with common organic reagents and their reactivity (e.g., LiAlH4, H2).
Basic understanding of reaction mechanisms.
Common mistakes
Using water or protic solvents with LiAlH4, which will quench the reagent and potentially cause an explosion.
Incomplete reduction, leading to the formation of imines as byproducts.
Using a catalyst that is poisoned or not active enough for complete reduction in catalytic hydrogenation.
Confusing the reduction of nitriles with other reactions of nitriles, like hydrolysis.
Practice preview
Which of the following reagents can be used for the reduction of nitriles to primary amines?…
easy
The reduction of a dinitrile like succinonitrile (NC-CH2-CH2-CN) using excess LiAlH4 followed by hydrolysis will yield:…
medium
The reduction of ethanenitrile (CH3CN) using LiAlH4 followed by hydrolysis yields:…
easy