How Aspirin Is Purified
Chemists have streamlined the process over time of making a synthetic version of medication so that it is not accompanied by the nasty side effects of, say, eating ground-up bark from a willow tree for pain. Today, the world is overpopulated with people who are plagued with daily aches and pains, and there simply aren’t as many willow trees available as in the old days. And let’s face it – not many people would take the time to strip the bark from a tree to grind up to ingest just to get rid of a headache. It’s much easier to swallow the same thing in pill form, and all it takes is half a second and a sip of water.
The process of purifying solid materials is called recrystallization. Basically, it is a process where a solid is placed in a liquid and heated to dissolve impurities. After the mixture cools, it turns back into crystals that are more pure than in the original solution. Three basic things are involved in the creation of the pain reliever: mixing salicylic acid with acetic anhydride and then adding some sulfuric acid make what we know as aspirin.
To synthesize aspirin, it must be isolated and purified, and then the purity is measured. The chemistry procedure is covered in many medical papers and is the subject of educational courses, as it’s such an important part of history.
To start, 3.0 grams of salicylic acid is placed in a flask, followed by 6.0 milliliters of acetic anhydride. A few drops of phosphoric acid are then added to act as a catalyst to allow the two liquids to mix evenly. The mixture has to be heated in warm water and then cooled in an ice bath. Crystals will form in the flask, a process called crystallization. Then the solid aspirin is filtered through a funnel and washed in cold water. After it sits, the water will evaporate to leave another batch of crystals, which are then dissolved, covered again, heated, and cooled to finish the recrystallization process.
Felix Hoffman was able to create a feasible form of aspirin to be manufactured in 1898 where German chemist Karl Johnson Kraut and French chemist Charles Frederic Gerhardt had failed years before. He did it by combining salicin molecules with acetyl chloride just over 25 years after the discovery of willow bark for pain relief in 1828. He realized it was actually salicin, the active ingredient in the tree bark, which helped with pain relief. German chemists identified it by its chemical name, salicylic acid, in 1838, and started making synthetic versions of the drug that had fewer side effects. The need for a synthetic version of aspirin was obvious by 1850, when the supply of willow trees couldn’t meet the demand. Scientists were finding so many new uses for the medicine that chemists were instructed to make a substitute that was just as good, if not better, than the original.