Preparation and Structure of Amines
Reduction of nitro compounds, Gabriel synthesis and Hoffmann bromamide reaction. (Chemistry › Amines and Diazonium Salts, NEET UG syllabus.)
What is Preparation and Structure of Amines?
Organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups.
Key formula / rule: Catalytic Hydrogenation of Nitro Compounds
Key points
- Describe the methods for preparing primary amines from nitro compounds, amides, and phthalimide.
- Identify the appropriate reagents and reaction conditions for each synthesis.
- Explain the limitations of Gabriel phthalimide synthesis.
- Predict the products of Hoffmann bromamide degradation.
Common exam trap
Attempting Gabriel synthesis with aryl halides or secondary/tertiary alkyl halides.
Definitions
- Term
Amine
- Meaning
Organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups.
- Term
Phthalimide
- Meaning
An organic compound with the formula C₆H₄(CO)₂NH, used as a starting material in Gabriel synthesis.
- Term
Isocyanate
- Meaning
An organic compound containing the functional group R-N=C=O, an intermediate in the Hoffmann bromamide degradation.
- Term
Degradation Reaction
- Meaning
A reaction that results in the loss of one or more carbon atoms from the parent molecule.
Learning objectives
Describe the methods for preparing primary amines from nitro compounds, amides, and phthalimide.
Identify the appropriate reagents and reaction conditions for each synthesis.
Explain the limitations of Gabriel phthalimide synthesis.
Predict the products of Hoffmann bromamide degradation.
Compare and contrast the different methods for amine preparation.
Formulae
- Name
Catalytic Hydrogenation of Nitro Compounds
- Note
Suitable for both aliphatic and aromatic nitro compounds.
- Expression
R-NO₂ + 3H₂ --(Pd/Pt/Ni)-→ R-NH₂ + 2H₂O
- Name
Reduction of Nitro Compounds with Metal and Acid
- Note
Fe/HCl is preferred industrially for aromatic nitro compounds.
- Expression
R-NO₂ + 6[H] --(Sn/HCl or Fe/HCl)-→ R-NH₂ + 2H₂O
- Name
Gabriel Phthalimide Synthesis (Overall)
- Note
R-X must be a primary alkyl halide. Aromatic amines cannot be prepared.
- Expression
Phthalimide --(KOH)-→ Potassium Phthalimide --(R-X)-→ N-alkylphthalimide --(H₂O/H⁺ or OH⁻ or NH₂-NH₂)-→ R-NH₂ (1° aliphatic amine)
- Name
Hoffmann Bromamide Degradation
- Note
Produces a primary amine with one carbon atom less than the starting amide.
- Expression
R-CONH₂ + Br₂ + 4NaOH → R-NH₂ + Na₂CO₃ + 2NaBr + 2H₂O
Prerequisites
Basic knowledge of functional groups (amines, amides, nitro compounds, alkyl halides).
Understanding of nucleophilic substitution (Sₙ2) reactions.
Concepts of oxidation and reduction in organic chemistry.
General reaction mechanisms.
Common mistakes
Attempting Gabriel synthesis with aryl halides or secondary/tertiary alkyl halides.
Forgetting that Hoffmann bromamide reaction results in a carbon atom loss.
Confusing reagents for different reduction methods.
Not recognizing the type of amine produced (primary, secondary, tertiary).
Keywords
Amines
Nitro compounds
Reduction
Gabriel synthesis
Hoffmann bromamide degradation
Phthalimide
Amides
Primary amines
Alkyl halides
Isocyanate
Practice preview
Which of the following reactions results in the formation of a primary amine with one carbon atom less than the starting material?…
medium
What is the product formed when nitrobenzene is reduced with H₂/Pd in ethanol?…
easy
The Hoffmann bromamide degradation reaction is used to prepare primary amines from which class of organic compounds?…
easy