1. To synthesize aspirin from salicylic acid and acetic anhydride. 2. To purify the crude product by Recrystallization.
Most drugs are chemical compounds which are described as "organic compounds" because they are comprised primarily of the elements carbon, hydrogen and oxygen. The present experiment will be the synthesis of a familiar organic compound called aspirin. The common chemical name is acetylsalicylic acid. Aspirin, the most widely used drug in the world, has an interesting history. Nearly 2500 years ago, Greeks reported that extracts of willow and poplar bark could be used to relieve pain and symptoms of illness. There are reports that American Indians, before the time of Columbus, used special teas made from the bark of willow trees to reduce fever. In 1763, the Reverend Edward Stone introduced these extracts and teas to the Europeans and in the early 1800's the active ingredient in willow bark (and in the flowers of the meadow sweet plant which had similar therapeutic characteristics) was isolated and identified as salicylic acid (from salix, the Latin name for the willow tree). Although salicylic acid could be synthesized in the laboratory and large quantities became available for therapeutic use in the mid 1800s, the compound's acidic properties caused irritation in the moist membranes of the mouth, throat and stomach. In 1875, the sodium salt was introduced and although the salt was less sour to the taste (actually it had an objectionable sweetish taste), it did not alleviate the gastric discomfort problems. [pic]
salicylic acid sodium salicylate
In 1893, Felix Hoffman Jr., a chemist working for the Bayer Laboratories in Germany, discovered a practical route for synthesizing an ester derivative of salicylic acid, acetylsalicylic acid. [pic]
Acetylsalicylic acid, a weaker acid than salicylic acid, was found to have the medicinal properties of salicylic acid without having the objectionable taste or producing the stomach problems. The acetyl group effectively masks the acidity of the drug during its ingestion and after it passes into the small intestine, it is converted back to salicylic acid where it can enter the bloodstream and do its pain relieving action. Bayer called its new product "aspirin," the name being derived from "a" for acetyl, and the root "-spir", from the Latin name Spiraea ulmaria, the meadow sweet flower, from which salicylic acid had been isolated. It was patented by Bayer in 1899, and in 1915 Bayer Aspirin tablets became commercially available as a non- prescription drug. The trademark is still owned by the Bayer A.G. company in Germany. Today, aspirin is one of the most widely used, commercially available pharmaceutical drugs in the world. Its properties make it a powerful analgesic (pain reliever), antipyretic (fever reducer) and anti-inflammatory (reduces swelling) drug. Aspirin is not without its faults. It still causes some stomach irritation in some individuals, and it has been estimated that about 1 mL of blood is lost from the stomach lining for each gram of aspirin consumed. Aspirin is known to interfere with normal blood clotting (which actually may be a benefit in preventing heart problems). Reye syndrome, a rare but serious illness has been associated with aspirin, and children and teenagers should not use aspirin for flu like symptoms before consulting a doctor. Synthesis
The salicylate ion forms the therapeutic part of the aspirin. Aspirin passes through the acidic stomach contents ad does not ionize and form the salicylate ion until it reaches the alkaline conditions in the intestines. Here it is hydrolyzed to form the acetate and salicylate ion. The latter ion is absorbed through the intestinal wall. The equation depicting...