Question

Aspirin Mechanism

1. Why prepare a hot water bath , using a hot plate to create a water bath for the erlenmeyer flask?
2. Within an empty erlenmeyer flask, add salicylic acid, acetic anhydride and sulfuric acid (catalyst) - why catalyst?
3. Why place the erlenmeyer flask in an ice bath? What does that help with?
4. Liquid acetic anhydride goes through conformation in the presence of H₃O - why?
5. Why does the salicylic acid attacks the acetic anhydride’s carbonyl carbon?
6. Is this a SN1 or SN2 reaction?
7. Is water is produced from this process?
8. How is this a substitution reaction?

Answer 1

Hot water bath is used to heat the reaction. Heating the teaction provides the activation energy for the reaction to occur.

H2SO4 is the catslyst that makes the reaction faster by protonating the acetic anhydride. Protonated acetic anhydtide os better electrophile than non-protonated acetic anhydride and thus makes the reaction faster.

After the reaction is complete; the erlenmeyer flask is cooled to crystallise the product from the reaction mixture.

In presence of H3O⁺; the carbonyl carbon of acetic anhydtide gets protonated.

The carbonyl carbon in acetic anhydride is electrohile as it gains a partial positive charge through resonance. The free IH group of slicylic acid is nucleophile and attacks the carbonyl carbon.

This is neither SN1 not SN2 because these nucleopholic substitution occurs at sp3 hybridised carbon. But here the electrophile; carbonyl carbon of acetic anhydride is sp2 hybridised.

Water is not produced here. The byproduct is acetic acid.

This is substitution because the OCOCH3 group of acetic anhydtide is substituted by the nuclrophile (salicylate).