Sunday, 17 August 2014

Aspirin extraction.

Acetylsalicylic Acid extraction from Aspirin.

In this experiment, we will extract acetylsalicylic acid.
Acetylsalicylic acid, the major component of Aspirin tablets (the rest being inherit binders etc) is a useful laboratory reagent that can be used a starting point for organic synthesis. Acetylsalicylic acid (ASA) may be hydrolysed to salicylic acid with reflux and an acid catalyst. Aspirin, a cheap, common painkiller can be had cheaply at local supermarkets, this box will be the source of (ASA) for this extraction experiment. This ASA will be used in future experiments including hydrolysis, esterification ( methyl salicylate) and many other experiments.

                                                          Safety and disposal:
Before attempting any experiment be sure to read all relevant safety information on the chemicals you will be handling/producing. In this experiment it is highly recommended to wear gloves, wear eye protection, wear a lab coat and work in a well ventilated area. Keep an appropriate fire extinguisher handy as isopropanol is highly flammable. Be sure to read all relevant disposal regulations, as it different depending on where you live the author can't give such information. The author of this blog will not be held responsible for any damage caused by following directly or indirectly instructions/ gaining information from this blog.

1. Firstly calculate the theoretical yield; The amount of tablets x the amount of ASA in each tablet.
 Chill in a freezer about 300 ml distilled or de-ionised water.
 This packet contains 7.2 g of
acetylsalicylic acid, the
maximum theoretical yield
of this extraction procedure;
24 tablets x 0.300 mg = 7.2 g

2. Measure about 1 ml of isopropanol per tablet (24 mL in my case) and add both aspirin and isopropanol in an appropriately sized Erlenmeyer flask.  
3.  Put some aluminium foil over the mouth of the flask and push through a thermometer until it is submerged by the isopropanol. Reflux the Erlenmeyer flask until all tablets are dissolved and broken down. Keep the temperature between 60-70° C (to minimise hydrolysis).

4. Once all tablets are broken down filter the solution and rinse the flask with a couple ml of isopropanol to quantitatively transfer all of the solution to the filter paper. Rinse the filter paper with a few ml of isopropanol and discard (ensure proper disposal).

5. To the filtered solution add 5x the amount of the solution in ice cold distilled or de-ionised water. this will precipitate the ASA from the solution as it is not highly soluble in  cold water-alcohol mixtures (more water than alcohol).
vacuum filter the precipitated ASA and wash with 3x 10 ml ice cold distilled or de-ionised water. Draw air over the product until dry and store in an appropriately labeled vial. weigh the product and calculate yield. Yield should be at least 80% with good lab technique.

 Additional notes
The product may be purified further with recrystallisation:
1. warm up about 50 ml of isopropanol
2. add ASA to beaker and then  add ( a little at a time) isopropanol until the aspirin dissolves and then filter.
3. allow isopropanol to evaporate at room temp the collect and store ASA. Done!
ASA hydrolyses at high temperatures and in with moisture so be sure to keep it in an air tight bottle!

No comments:

Post a Comment