AQA Chemistry A-level: Amines (3.3.11)

Preparation of Amines

Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with organic groups. They can be classified into:

• Primary (1º) amines: One hydrogen atom replaced
• Secondary (2º) amines: Two hydrogen atoms replaced
• Tertiary (3º) amines: Three hydrogen atoms replaced

Methods of Production

1. Nucleophilic Substitution

   • Halogenoalkanes react with ammonia in a sealed tube to produce primary amines and ammonium salts.
   • Reaction can lead to multiple substitutions resulting in a mixture of products.
   • To improve efficiency:
     • Use excess ammonia to favor the production of primary amines.
     • Separate products using fractional distillation.

2. Reduction of Nitriles

   • Amines can be produced by hydrogenating nitriles using:
     • LiAlH₄ (a reducing agent) and acidic conditions.
     • Hydrogen and Nickel for catalytic hydrogenation.

3. Aromatic Amines

   • Produced by reducing nitrobenzene using concentrated HCl and a Tin catalyst.

4. Cationic Surfactants

   • Molecules with positive and negative ends, useful in preventing static on surfaces and employed in industrial applications.

Amine Base Properties

• Amines are weak bases due to the lone pair of electrons on nitrogen that can accept protons.
• Base strength depends on the availability of the electron pair:

Inductive Effect

1. Benzene Rings

   • Draw electron density away from nitrogen, making it less available.
   • Exhibits a negative inductive effect.

2. Alkyl Groups

   • Push electron density towards nitrogen, enhancing availability.
   • More alkyl groups intensify this effect.
   • Exhibits a positive inductive effect.

• Aliphatic amines are stronger bases compared to aromatic amines.

Nucleophilic Properties

Nucleophilic Substitution

• Amines act as nucleophiles due to their lone electron pairs.
• Can substitute halides on halogenoalkanes to form amines and quaternary ammonium salts.

Nucleophilic Addition-Elimination

• Amines react with acyl chlorides to produce amides and N-substituted amides.
• Similarly, they react with acid anhydrides to yield an amide and a carboxylic acid.

N-substituted Amides

• Naming is similar to esters, focusing on the substitution pattern.

These notes provide an overview of amine preparation, properties, and reactions as covered in the AQA Chemistry A-level syllabus. The key topics include their synthesis, base properties, and nucleophilic behaviors.