Preparation of Aspirin from Salicylic Acid
Objective: To prepare of Aspirin (Acetyl Salicylic acid) from Salicylic acid.
Apparatus/Glassware Required: 125 mL Erlenmeyer flask, beaker, volumetric flask, measuring cylinder, steam bath, suction pump, Buchner funnel, filter papers etc.
Chemicals Required: Salicylic acid, acetic anhydride, concentrated sulphuric acid and alcohol
The principle involved in the preparation of aspirin is O-Acetylation. It involves the replacement of one of the hydrogen atom by -COCH3 group. Salicylic acid interacts with acetic anhydride in the presence of few drops of concentrated sulphuric acid to produce aspirin. The purpose of adding sulphuric acid (catalyst) is to aid and augment the process of detaching the acetate ion from acetic anhydride which ultimately gets associated with H+ ion from phenolic hydroxyl group in salicylic acid to be eliminated as a mole of acetic acid. The excess acetic acid will be quenched with the addition of water. The aspirin product is not very soluble in water so the aspirin product will precipitate when water is added.
For Chemical Reaction(Click Download Tab)
- Place 2.0 g (0.015 mol) of salicylic acid in a 125-mL Erlenmeyer flask.
- Add 5 mL (0.05 mol) of acetic anhydride, followed by 5 drops of conc. H2SO4 and swirl the flask gently until the salicylic acid dissolves.
- Heat the flask gently on the steam bath at 50-60oC for at least 10-15 minutes.
- Allow the flask to cool to room temperature. If acetylsalicylic acid does not begin to crystallize out, scratch the walls of the flask with a glass rod. Cool the mixture slightly in an ice bath until crystallization is completed. The product will appear as a solid mass when crystallization is completed.
- Add 50 mL of water and cool the mixture in an ice bath. Do not add the water until crystal formation is complete.
- Filter the product using a Buchner funnel. You can use some of the filtrate to rinse the Erlenmeyer flask if necessary.
- Rinse the crystals several times with small portions (5 mL) of cold water and air dry the crystals on a Buchner funnel by suction until the crystals appear to be free of solvent. Test this crude product for the presence of unreacted salicylic acid using the ferric chloride test.
- It is recrystallized from 50% alcohol.
- It is used extensively in medicine as a pain killer (analgesic) and as a fever-reducing drug (antipyretic).
- It reduces the risk of transient ischemic attacks in men.
- It is a white, crystalline, weakly acidic substance.
- The melting point of aspirin is 138-140 °C.
- Wear goggles throughout this experiment.
- The salicylic acid and aspirin may cause irritation to your skin or eyes, but are basically not hazardous. An excess of these can be disposed of in the sink or, if packaged, in the trash. If you spill some, wipe it up with a wet paper towel and throw the towel in the trash.
- The acetic anhydride and sulfuric acid can cause bad burns. Use them only in the hood and be sure the hood fan is on! Wear gloves when using these chemicals.
- If you spill a lot of either of these, notify your instructor.
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Last Updated : 20-07-2018 02:36:38 pm
Madhusudhana Reddy Induri
Dr. Reddy working as Associate Professor, Department of Pharmaceutical Analysis, KVSR Siddhartha College Pharmaceutical Sciences, Vijayawada