Esters are hydrolyzed either by aqueous base or acid to yield carboxylic acids plus alcohols.
In base-catalyzed hydrolysis (saponification), a hydroxide ion attacks the ester carbonyl to produce a tetrahedral alkoxide intermediate. Elimination of the alkoxide ion generates the carboxylic acid, which is immediately deprotonated by the alkoxide ion. An acid work-up restores the carboxylic acid.
Acid-catalyzed hydrolysis can occur by more than one mechanism, depending on the structure of the ester. In a reverse Fisher esterification, the carbonyl group is protonated by the acid, which activates it for nucleophilic attack by water, yielding a tetrahedral intermediate. Transfer of a proton and elimination of alcohol yields the carboxylic acid.
- Reagents:Acid or Base
- Reactant: Ester
- Product: Alcohol, Carboxylic Acid
- Type of Reaction: Nucleophilic Acyl Substitution
- Bond Formation: RCO2H
Lab Tips
- Sensitive functional groups on the starting material may get cleaved under acidic or basic conditions. [1][1]
- Reflux in an aqueous suspension of Dowex-50 is another option for obtaining the corresponding carboxylic acid in good yield. [2]
- Most protocols developed for the hydrolysis of hindered esters require stringent conditions that affect other functional groups. [3]
2. Basu, M. K., Sarkar, D. C., Ranu, B. C. A mild and selective method of ester hydrolysis. Synthetic Communications – An International Journal for Rapid Communication of Synthetic Organic Chemistry 1989, 19(3-4), 627-631.
3. Huffman, J. W., Harris, P. R. A convenient procedure for the hydrolysis of hindered esters. Synthetic Communications – An International Journal for Rapid Communication of Synthetic Organic Chemistry 1976, 6(7), 481-484.
Mechanism
Top Citations
Related Reactions
- Fischer Esterification
Related Compounds
- Acid or Base
