Overview
This lecture covers the hydrolysis of esters in organic chemistry, focusing on both acid-catalyzed and base-catalyzed (saponification) mechanisms, including product prediction and key differences.
Hydrolysis of Esters: Introduction
- Hydrolysis means "cutting with water" and is the reverse of esterification.
- Involves breaking the ester bond using water, resulting in two products.
- Two main types: acid-catalyzed hydrolysis and base-catalyzed hydrolysis (saponification).
Acid-Catalyzed Hydrolysis
- Requires water and a strong acid catalyst (e.g., HCl, H₂SO₄, HNO₃).
- Produces the original alcohol and carboxylic acid that formed the ester.
- Mechanism involves breaking the ester bond and adding an H to the alkoxy group (forms alcohol) and an OH to the acyl group (forms carboxylic acid).
- Reaction changes the pH and properties of the solution.
- Product prediction requires accounting for all carbons and listing both products.
Base-Catalyzed Hydrolysis (Saponification)
- Performed with a strong base (e.g., NaOH or KOH) and heat in aqueous solution.
- Produces a carboxylate salt (e.g., sodium acetate) and an alcohol.
- The reaction is similar to a double replacement, "trading positives" between the ester and the base.
- The formed salt is ionic, affecting solubility, and is a key component in soap making.
- Always include ionic charges in the product structures.
Examples and Practice
- When predicting products, always ensure the total number of carbons remains unchanged.
- Acid hydrolysis yields an alcohol and a carboxylic acid.
- Base hydrolysis yields an alcohol and a carboxylate salt (with the metal from the base).
- Naming carboxylate salts follows: metal name + acid name (e.g., sodium acetate).
- Methanol or ethanol can be formed as the alcohol, depending on the ester.
Key Terms & Definitions
- Hydrolysis — Chemical process of breaking bonds with water.
- Ester — Compound with the functional group RCOOR′.
- Acid-Catalyzed Hydrolysis — Ester hydrolysis using acid to produce alcohol and carboxylic acid.
- Base-Catalyzed Hydrolysis (Saponification) — Ester hydrolysis using base to produce alcohol and carboxylate salt.
- Carboxylate Salt — Ionic compound formed from a carboxylic acid and a metal (e.g., sodium acetate).
Action Items / Next Steps
- Practice writing and predicting products for both acid- and base-catalyzed hydrolysis of esters.
- Ensure all product carbons are accounted for in reaction equations.