High School Chemistry
A level Chemistry practical to produce an organic solid and purify it.
One required practical on the A level Chemistry syllabus that is widely used is the production of aspirin by the reaction of 2-hydroxybenzoic acid with ethanoic anhydride.
But, what to do if ethanoic anhydride is banned in your location?
One possibility is to do a hydrolysis of aspirin, essentially the reverse of the above mentioned reaction.
In this video clip 6 aspirin tablets and 100ml of sodium hydroxide, 0.4M are used. The reaction was stirred overnight at room temperature, around 26 C.
The next day the reaction mixture was acidified using 25ml of hydrochloric acid, 2M. The product of the reaction precipitated out and was removed by filtration under reduced pressure.
Next steps, not shown in the video clip, are to dry the filtered solid and then recrystallise from ethanol.
In another experiment, the precipitated solid was allowed to dry over the weekend. It was then dissolved in the minimum volume of hot ethanol, filtered and allowed to crystallise. A sample from this procedure had a melting point within 1 C of commercial 2-hydroxybenzoic acid in the school chemical store.
Recrystallised solid 149 C
Chemical store 2-hydroxybenzoic acid 150 C
Both of these values recorded by A level chemistry students in the school laboratory are below the accepted literature value.
e.g. Melting point of 2-hydroxybenzoic acid 158.6 C Wikipedia
en.wikipedia.org/wiki/Salicylic_acid
Unfortunately, we were unable to carry out a thin layer chromatography experiment to investigate the purity of the hydrolysis product further.
Thanks to Dr Gavan Cooke for operating the vacuum pump for reduced pressure filtration using a Buchner funnel seen at the end of the video clip.
If we were to repeat the experiment we would acidify the hydrolysis mixture more gradually.
KAKW4470