Return to Contents Chapter 27: Amino Acids, Peptides and Proteins Ch 27 contents
Preparation of Esters
(review of Chapter 19)
esterification of carboxylic acids
Reaction type:  Nucleophilic Acyl Substitution


Study Tip:
The carboxylic acid and alcohol combination used to prepare an ester are reflected by the name of the ester,  e.g. ethyl acetate (or ethyl ethanoate), CH3CO2CH2CH3  can be made from CH3CO2H, acetic acid (or ethanoic acid) and HOCH2CH3 (ethanol).  This general "disconnection" is shown below:
disconnecting esters

Step 1:
An acid/base reaction. Protonation of the carbonyl makes it more electrophilic.
acid cat. esterification
Step 2:
The alcohol O functions as the nucleophile attacking the electrophilic C in the C=O, with the electrons moving towards the oxonium ion, creating the tetrahedral intermediate.
Step 3:
An acid/base reaction. Deprotonate the alcoholic oxygen.
Step 4:
An acid/base reaction. Need to make an -OH leave, it doesn't matter which one, so convert it into a good leaving group by protonation.
Step 5:
Use the electrons of an adjacent oxygen to help "push out" the leaving group, a neutral water molecule.
Step 6:
An acid/base reaction. Deprotonation of the oxonium ion reveals the carbonyl in the ester product.

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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary