Preparation of aspirin Flashcards
Reactants
2-hydroxybenzoic acid + ethanoic anhydride
Structure of 2-hydroxybenzoic acid
Benzene with carboxylic acid group
And OH (phenol group) bonded to adjacent carbon
Structure of ethanoic anhydride
Ether group bonded to 2 carbon on either end
These carbons are double bonded to an oxygen each C=O
and a methyl group each too
Process of esterification in making aspirin
Phenol group on 2-hydroxybenzoic acid becomes ester group: H leaves
H3C-C=O from ethanoic anhydride bonds to left over O on the 2-hydroxybenzoic acid
Forms aspirin
Waste product in this reaction
Ethanoic acid
Rest of ethanoic anhydride becomes Ethanoic acid because H from phenol group bonds to oxygen
why use ethanoic anhydride instead of acyl chloride?
because it is cheaper, less
corrosive, less vulnerable to hydrolysis,
and less dangerous to use.
Preparing reaction mixture to make aspirin
Add to pear-shaped flask 2.0 g of 2-hydroxybenzoic acid and
4 cm3 of ethanoic anhydride+ 5 drops of 85% phosphoric(v) acid and swirl to mix
Reflux mixture by heat with boiling water
Without cooling the mixture,
carefully add 2 cm3of water in one portion down the condenser
Inducing crystallisation of aspirin
When the vigorous reaction has ended, pour the mixture into 40 cm3 of cold water in a beaker, stir and rub the sides of the beaker with a stirring rod necessary to induce crystallisation and, finally, allow the mixture to stand in ice bath to complete crystallisation.
Collect the product by suction filtration and wash it with a little water
Purification by recrystallisation
Redissolve aspirin in hit ethanol = hot filtration to separate insoluble impurities
Collect filtrate and leave to cool with cold water bath so aspirin recrystallises
Complete cold filtration with cold ethanol = obtain crystals of pure aspirin
Solvent used in purification
Ethanol
