Investigating the purity of Aspirin
Investigating Aspirin
Aims
Synthesize my own aspirin
Analyse the purity of my aspirin samples (aspirin and recrystallized aspirin) compared to commercial aspirin by use of analysing melting points, TLC plates and colorimetry tests
Investigate how pH effects the rate of hydrolysis of aspirin
Background theory
Making my own sample of Salicylic acid (to then be converted into Aspirin)
Salicylic acid (2-Hydroxybenzoic acid) can be made by hydrolysing methyl 2-hydroxybenzoate. Oil of wintergreen is 98% methyl 2-hydroxybenzoate and is what I used as my starting chemical. The structure of methyl-2-hydroxybenzoate is shown on the right, and is an ester as it has the functional group –COO-. Hydrolysing esters involves splitting them into carboxylic acids or their salts and alcohols by adding water, dilute acid or dilute alkali. To hydrolysed my oil of wintergreen I first reacted it with a weak alkali, aqueous sodium hydroxide, and heated it under reflux to produce sodium 2-hydroxybenzoate. I then converted this into 2-hydroxybenzoic acid by adding hydrochloric acid.
Technically, hydrolysis is a reaction with water, however, the exact thing happens when acids/alkalis hydrolyse esters, the reaction is just quicker as the acid/alkali acts as a catalyst.
To hydrolyse the methyl-2-hydroxybenzoate it is heated under reflux with the dilute alkali sodium hydroxide.
First we hydrolyse the methyl-2-hydroxybenzoate using aqueous sodium hydroxide:
The sodium salt, sodium 2-hydroxybenzoate, is formed rather than the carboxylic acid itself (which is what we want). To get the acid (Salicylic acid) we now react the sodium 2-hydroxybenzoate with an excess of conc. Hydrochloric acid. Doing this floods the mixture with hydrogen ions which are picked up by the hydroxybenzoate ions present in the sodium salt to make 2-Hydroxybenzoic acid (salicylic acid) as shown below.
The 2-hydroxybenzoic acid can now be filtered off and we have our sample of
Aims
Synthesize my own aspirin
Analyse the purity of my aspirin samples (aspirin and recrystallized aspirin) compared to commercial aspirin by use of analysing melting points, TLC plates and colorimetry tests
Investigate how pH effects the rate of hydrolysis of aspirin
Background theory
Making my own sample of Salicylic acid (to then be converted into Aspirin)
Salicylic acid (2-Hydroxybenzoic acid) can be made by hydrolysing methyl 2-hydroxybenzoate. Oil of wintergreen is 98% methyl 2-hydroxybenzoate and is what I used as my starting chemical. The structure of methyl-2-hydroxybenzoate is shown on the right, and is an ester as it has the functional group –COO-. Hydrolysing esters involves splitting them into carboxylic acids or their salts and alcohols by adding water, dilute acid or dilute alkali. To hydrolysed my oil of wintergreen I first reacted it with a weak alkali, aqueous sodium hydroxide, and heated it under reflux to produce sodium 2-hydroxybenzoate. I then converted this into 2-hydroxybenzoic acid by adding hydrochloric acid.
Technically, hydrolysis is a reaction with water, however, the exact thing happens when acids/alkalis hydrolyse esters, the reaction is just quicker as the acid/alkali acts as a catalyst.
To hydrolyse the methyl-2-hydroxybenzoate it is heated under reflux with the dilute alkali sodium hydroxide.
First we hydrolyse the methyl-2-hydroxybenzoate using aqueous sodium hydroxide:
The sodium salt, sodium 2-hydroxybenzoate, is formed rather than the carboxylic acid itself (which is what we want). To get the acid (Salicylic acid) we now react the sodium 2-hydroxybenzoate with an excess of conc. Hydrochloric acid. Doing this floods the mixture with hydrogen ions which are picked up by the hydroxybenzoate ions present in the sodium salt to make 2-Hydroxybenzoic acid (salicylic acid) as shown below.
The 2-hydroxybenzoic acid can now be filtered off and we have our sample of