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Alkaline hydrolysis of esters is also known as saponification. A base such as sodium hydroxide is required in stochiometric amounts. Unlike acid-catalyzed ester hydrolysis, it is not an equilibrium reaction and proceeds to completion. Hydroxide ion attacks the carbonyl carbon to give a tetrahedral intermediate, which then expels an alkoxide ion.
S N 1 ether cleavage is generally faster than S N 2 ether cleavage. However, reactions that would require the formation of unstable carbocations (methyl, vinyl, aryl or primary carbon) proceed via S N 2 mechanism. The hydrohalic acid also plays an important role, as the rate of reaction is greater with hydroiodic acid than with hydrobromic acid
Saponification is a process of cleaving esters into carboxylate salts and alcohols by the action of aqueous alkali. Typically aqueous sodium hydroxide solutions are used. [1] [2] It is an important type of alkaline hydrolysis. When the carboxylate is long chain, its salt is called a soap. The saponification of ethyl acetate gives sodium acetate ...
[2] Pig liver esterase (PLE) is a widely used enzyme for asymmetric ester hydrolysis. Although it was originally used for the desymmetrizing hydrolysis of glutarate esters, [3] PLE also hydrolyzes malonates, cyclic diesters, monoesters, and other substrates. Active site models have been advanced to explain the selectivity of PLE. [4] (1)
Scheme 2. Hydrolysis of benzoic acid esters. Reaction constants are known for many other reactions and equilibria. Here is a selection of those provided by Hammett himself (with their values in parentheses): the hydrolysis of substituted cinnamic acid ester in ethanol/water (+1.267) the ionization of substituted phenols in water (+2.008)
Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. [1] Strong acids catalyze the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile.
Ortho esters are readily hydrolyzed in mild aqueous acid to form esters: . RC(OR ′) 3 + H 2 O → RCO 2 R ′ + 2 R ′ OH. For example, trimethyl orthoformate CH(OCH 3) 3 may be hydrolyzed (under acidic conditions) to methyl formate and methanol; [5] and may be further hydrolyzed (under alkaline conditions) to salts of formic acid and methanol.
The hydrolysis of esters can occur through either acid and base catalyzed mechanisms, both of which proceed through a tetrahedral intermediate. In the base catalyzed mechanism the reactant goes from a neutral species to negatively charged intermediate in the rate determining (slow) step , while in the acid catalyzed mechanism a positively ...