Aspirin – Chemistry Flashcard

What is overall? the reaction for synthesis of aspirin
It involves an esterification reaction between salicylic acid and acetic anhydride in the presence of sulfuric acid in order to generate acetylsalicylic acid.
What are the three characteristics of a catalyst?
(1) increasing the reaction rate by lowering the activation energy
(2) involved in reaction but is not consumed, same amount recovered
(3) activate electrophile/nucleophile
What are the three ways we can catalyze the aspirin reaction?
Activation of the nucleophile
Activation of the electrophile
Activation of both the nucleophile and electrophile
acid catalyst
involve making the electrophile more electrophilic by protonation ( H2SO4) or by coordination (BF3)
Base catalysis
involves developing a better nucleophile by hydrogen abstraction of the original species, rendering it anionic. An example of base catalysis would be the use of sodium bicarbonate. Bases catalyze nucleophile while acids catalyze electrophiles.
Bronsted acid catalyst
proton donor
carbonyl chemistry
– classic electrophile
– oxygen is more electronegative than carbon, so it draws electron density from carbon to increase bond polarity
– protonation by hydrogen makes it more electrophilic, which generates a positive partial charge on oxygen
– acetic anhydride is an even more potent electrophile since the leaving group for the carbonyl oxygen is electronegative
Draw the reaction mechanism
Why do we use an excess amount of acetic anhydride?
1) acetic anhydride slowly undergoes hydrolysis ( reacts with water) under the reaction conditions and become two molecules of acetic acid.
2) According to Le Chatlier’s principle, if more acetate is continuously produced as a product, the reaction will revert backwards to the reagents in order to achieve equilibrium. In order to account for this possible reduction in yield, excess acetic anhydride is used in order to drive the reaction forward. Although acetic acid can still react with salicylic acid to generate aspirin, it is a relatively slow process that produces poor yield. Thus, acetic anhydride makes a better solvent as its anhydride portion reacts with water.
What are the three side products that can occur?
1) polymer formation
2) hydrolysis of acetic anhydride
3) regeneration of starting material
Polymer formation
Polymer formation can occur when an anion of the salicylic acid attacks the mixed anhydride to form polyester via esterification. This process can continuously repeat itself, eventually making it difficult to recover product
hydrolysis of acetic anhydride
acetic anhydride slowly undergoes hydrolysis causing it to decompose into two molecules of acetic acid due to water’s ability to act as a nucleophile.
regeneration of starting material
most likely side product after purification is the reagent salicylic acid itself, which can regenerate in the presence of excess water. During this hydrolysis reaction, water can attack the acetylsalicylic acid, forming a tetrahedral intermediate. The tetrahedral intermediate that is bonded to the oxygen connected to the phenol group is cleaved to form salicylic acid and acetic anhydride. Since esterification reactions are slow and reversible, concentrated sulfuric acid is useful to observe more product yield
What kind of solvent should be used for crystallization?
One that does not dissolve the solute very well
Ferric chloride test
– tests for presence of phenols and thereby differentiates between salicylic acid and acetylsalycilic acid
-originally light brown but turns deep violet if there is phenol
-tests positive for salicylic acid and impure acetyl salicylic acid
Iodine test
– detects starch
-changes from orange-red-brown to purple-black color
– tests positive for the aspirin tablet

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