Synthesis of Aspirin: Introduction to Organic Chemistry

Overview

• Objective: Learn to synthesize aspirin from starting materials.

Materials Required

• Salicylic Acid
  • Measure 1 gram using a milligram balance.
  • Place into a 6-inch test tube.
• Acetic Anhydride
  • Measure 2.5 mL using a graduated cylinder.
  • Pour into the test tube with salicylic acid.
• Phosphoric Acid
  • Add 3 drops carefully, one at a time, stirring between each drop.
• Hot Water Bath
  • Use at 78.6°C for 15 minutes, stirring occasionally.

Procedure

Reaction

1. Combine salicylic acid, acetic anhydride, and phosphoric acid in a test tube.
2. Place the test tube in a hot water bath for 15 minutes.
   • Reaction forms aspirin.

Product Isolation

3. Remove the test tube and place it in an ice bath.
4. Gradually add 10 mL of chilled DI water.
   • Add in small portions, stirring to form aspirin.
5. Vacuum filtration setup:
   • Connect the tubing to the filter flask and the sink.
   • Weigh a filter paper and weigh boat together: 2.652 grams.
6. Place filter paper on the funnel, wet with a small amount of water.
7. Pour the product onto the filter, use a stirring rod for assistance.
8. Rinse with 5 mL of ice-cold DI water.
   • Spread the product for even drying.
9. Allow the product to dry on the filter paper.
10. Transfer dried product into a dish for complete drying and future weighing.

Standard Solution Preparation

• Standard Salicylic Acid Solution
  • Add 5 mL in a 25 mL volumetric flask using a glass pipette.
  • Add 2.5 mL of 95% ethanol.
  • Add 2.5 mL of iron solution, turns purple.
  • Fill to line with DI water, stoppered and invert 15 times.

Spectrometer Calibration

• Set spectrometer to 525 nm for maximum wavelength.
• Ensure two cuvettes match by comparing DI water readings.
• Measure transmittance of the standard solution.

Day 2: Product Recrystallization and Analysis

• Weigh Dry Product: Record weight: 3.655 grams.
• Recrystallization:
  • Use 0.2 grams of crude product.
  • Use hot water bath to dissolve product fully.
  • Add 2.5 mL of 95% ethanol, then 5 mL of pre-warmed DI water.
  • Allow to cool, initiate crystals with an ice bath.

Final Product Analysis

• Use spectrometer to determine salicylic acid concentration in aspirin.
• Measure percent transmittance and molar absorptivity.
• Calculate percent yield based on recrystallized product weight.

Waste Management

• All waste products can be disposed of down the sink.
• Clean and return all equipment to the stockroom.

These notes summarize the process of aspirin synthesis in an introductory organic chemistry lab, covering reaction details, product isolation, and analysis steps.