Nitrogen compounds

🔹 Primary Amines

🔸 Preparation of Primary Amines

Method:

• Reagent: Excess ammonia (NH₃)
• Reactant: Halogenoalkane (e.g., bromoethane)
• Solvent: Ethanol (to dissolve both organic and inorganic reactants)
• Condition: Heat under pressure in a sealed tube

Reaction:

Where:

• R–X = halogenoalkane (X = Cl, Br, or I)
• R–NH₂ = primary amine
• NH₄X = ammonium halide (by-product)

Mechanism: Nucleophilic substitution

• Ammonia acts as a nucleophile and attacks the electrophilic carbon bonded to halogen.

Notes:

• Excess ammonia helps reduce further substitution (formation of secondary/tertiary amines).
• Classification of amines (primary, secondary, tertiary) is not required at AS Level.

🔹 Nitriles and Hydroxynitriles

🔸 (1) Preparation of Nitriles

Method:

• Reagent: Potassium cyanide (KCN)
• Reactant: Halogenoalkane
• Solvent: Ethanol
• Condition: Heat

Reaction: R–X + KCN → R–CN + KX

Mechanism: Nucleophilic substitution

• CN⁻ ion acts as a nucleophile, replacing the halogen atom.

Importance:

• This is a useful method to extend the carbon chain by one carbon atom.

🔸 (2) Preparation of Hydroxynitriles (α-hydroxynitriles)

Method:

• Reactants: Aldehyde or ketone
• Reagents: Hydrogen cyanide (HCN)
• Catalyst: Potassium cyanide (KCN)
• Condition: Heat

Reaction Example: CH₃CHO + HCN → CH₃CH(OH)CN

(Ethanal → 2-Hydroxypropanenitrile)

Mechanism:

• Nucleophilic addition:
  1. CN⁻ attacks the carbonyl carbon.
  2. The oxygen picks up a proton (H⁺) forming the hydroxyl group.

Notes:

• Hydroxynitriles contain both an –OH and a –CN group.
• This reaction is stereoselective: a new chiral center is formed in most cases.

🔸 (3) Hydrolysis of Nitriles to Carboxylic Acids

Two methods:

1. Acidic hydrolysis:
   • Reagent: Dilute HCl (or H₂SO₄)Condition: Heat under reflux
   R–CN + 2H₂O + HCl → R–COOH + NH₄Cl
2. Alkaline hydrolysis (followed by acidification):
   • Reagent: Dilute NaOH or KOHCondition: Heat under refluxFollowed by: Acidification using dilute HCl or H₂SO₄
   R–CN + NaOH + H₂O → R–COO⁻Na⁺ + NH₃

Purpose: Converts the –CN group into –COOH, useful in organic synthesis.

🔚 Summary Table

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