Esteres

Reactions of Esters
Esters can be converted into other esters (transesterification), the parent carboxylic acid (hydrolysis) or amides o
* Transesterification : heat with alcohol and acidcatalyst
* Hydrolysis : heat with aq. acid or base (e.g. aq. H2SO4 or aq. NaOH)
* Amide preparation : heat with the amine, methyl or ethyl esters are the most reactive.

Hydrolysis of EstersReaction type: Nucleophilic Acyl Substitution
Summary
Carboxylic esters hydrolyze to the parent carboxylic acid and an alcohol.
Reagents : aqueous acid (e.g. H2SO4) / heat, or aqueous NaOH /heat (known as "saponification").
These mechanisms are among some of the most studied in organic chemistry.
Both are based on the formation of a tetrahedral intermediate which then dissociates.
Inboth cases it is the C-O bond between the acyl group and the oxygen that is cleaved.

Reaction under “ basic” conditions:
* The mechanism is supported by experiments using 18O labeledcompounds and esters of chiral alcohols.
* This reaction is known as "saponification" because it is the basis of making soap from glycerol triesters in fats.
* The mechanism is an example of thereactive system type.
Mechanism of the base hydrolysis of esters
* Step 1:
The hydroxide nucleophiles attacks at the electrophilic C of the ester C=O, breaking the  bond and creating thetetrahedral intermediate.
* Step 2:
The intermediate collapses, reforming the C=O
results in the loss of the leaving group the alkoxide, leading to the carboxylic acid.
* Step 3:
An acid / basereaction. A very rapid equilibrium where the alkoxide functions as a base deprotonating the carboxylic acid (an acidic work up would allow the carboxylic acid to be obtained from the reaction).Reaction under “acidic” conditions:
* Note that the acid catalyzed mechanism is the reverse of the Fischer esterification.
* The mechanism shown below also leads to acyl-oxygen cleavage....