Preparation of Benzoic Acid

Objective

• Convert benzyl alcohol into benzoic acid.

Reaction Overview

• Starting Material: Benzyl alcohol
• Oxidizing Agent: Potassium permanganate
• Product: Benzoic acid

Chemical Reaction

• Functional Group Transformation:
  • Remove two hydrogens from benzyl alcohol
  • Add oxygen to form the carboxylic group (OH group with double bond O)

Materials Required

• Benzyl alcohol
• Potassium permanganate (0.5 M solution)
• Sodium carbonate (anhydrous)
• Sodium sulfite
• Hydrochloric acid
• Conical flask
• Water bath
• Buchner filtration apparatus

Procedure

Reaction Setup

1. Benzyl Alcohol Addition:
   • 1 mL of benzyl alcohol placed in a conical flask.
2. Sodium Carbonate:
   • 0.5 g of anhydrous sodium carbonate pre-wet in sample vials.
3. Oxidizing Agent Addition:
   • Add 25 mL of 0.05 M potassium permanganate.

Oxidation Reaction

• Mixing:
  • Mix for 15-20 minutes at 60°C using a water bath and Bunce burner.
• Observation:
  • Brown color of potassium permanganate indicates oxidation (Manganese changes from +7 to +4).

Neutralization

1. Cool Down Reaction:
   • Cool to 25°C using a water bath.
   • Check basicity with red litmus paper (turns blue).
2. Acid Addition:
   • Add ~25 mL of hydrochloric acid until reaction is neutral (blue litmus turns red).

Precipitation and Filtration

1. Sodium Sulfite Addition:
   • Add dropwise until brown precipitate disappears.
   • Benzoic acid crystals form in solution.
2. Buchner Filtration:
   • Set up apparatus with matching filter paper.
   • Wet paper with ionized water, place funnel, create suction.
   • Pour mixture into funnel, crystals remain on filter paper.
   • Swirl flask to collect additional crystals.

Result

• Observation:
  • Benzoic acid crystals form on the filter paper.
  • Dry and weigh crystals to calculate percentage yield.

Key Points

• Maintain reaction temperature at 60°C during oxidation.
• Ensure complete neutralization after cooling.
• Efficient filtration and collection of crystals are crucial for product isolation.