Aspirin

About 2500 years ago, the ancient Greeks used the leaves and bark of the willow tree to ease pain.

About 250 years ago, the royal society discussed the pain relieving effects of chewing bark.

The search for the active ingredient was on. It was eventually isolated in 1828 and named salicylic acid.

Unfortunately it caused mouth ulcers and reacted with the stomach lining.

In 1897, aspirin (acetylsalicylic acid) was first synthesised. It didn’t irritate the stomach like plain salicylic acid.

METHOD - Mix salicylic acid with a substance called ethanoic anhydride, and add a few drops of concentrated sulphuric acid. Heat the mixture to 50 degrees C for a few minutes. Acetylsalicylic acid is formed and precipitates out as a solid on cooling. You can filter it out, and crystallise it.

The industrial method is similar, but is more ********. Salicylic acid is mixed with ethanoic anhydride and an organic solvent. The mixture is heated to 90 degrees C for 24 hours and then cooled for 3-4 days.