Return to Contents  Chapter 20: Carboxylic Acid Derivatives. NucleophilicAcyl Substitution  Ch 20 contents

Hydrolysis of Esters

hydrolysis of esters

Reaction type:  Nucleophilic Acyl Substitution

Summary

Related Reactions Reaction under BASIC conditions:
MECHANISM OF THE BASE HYDROLYSIS OF ESTERS

Step 1:
The hydroxide nucleophiles attacks at the electrophilic C ofthe ester C=O, breaking the π bond and creating the tetrahedral intermediate.
hydrolysis of an ester using hydroxide
Step 2:
The intermediate collapses, reforming the C=O
results in the loss of the leaving group the alkoxide, RO-, leading to the carboxylic acid.
Step 3:
An acid / base reaction. A very rapid equilibrium where the alkoxide,RO- functions as a base deprotonating the carboxylic acid, RCO2H, (an acidic work up would allow the carboxylic acid to be obtained from the reaction).
 

Reaction under ACIDIC conditions:

MECHANISM OF THE ACID CATALYSED  HYDROLYSIS OF ESTERS
Step 1:
An acid/base reaction. Since we only have a weak nucleophile and a poor electrophile we need to activate the ester. Protonation of the ester carbonyl makes it more electrophilic.
hydrolysis of an ester with acid catalysis
Step 2:
The water 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 oxygen that came from the water molecule to neutralise the charge.
Step 4:
An acid/base reaction. Need to make the -OCH3 leave, but need to convert it into a good leaving group first by protonation.
Step 5:
Use the electrons of an adjacent oxygen to help "push out" the leaving group, a neutral methanol molecule.
Step 6:
An acid/base reaction. Deprotonation of the oxonium ion reveals the carbonyl C=O in the carboxylic acid product and regenerates the acid catalyst.

previous page
next page
© Dr. Ian Hunt, Department of Chemistry, University of Calgary