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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.
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. The resulting carboxylic acid quickly protonates the alkoxide ion to give a carboxylate ion and an alcohol. [1]
The hydroxide anion adds to the carbonyl group of the ester. The immediate product is called an orthoester. Saponification part I. Expulsion of the alkoxide generates a carboxylic acid: Saponification part II. The alkoxide ion is a strong base so the proton is transferred from the carboxylic acid to the alkoxide ion, creating an alcohol:
The final step in the reduction of carboxylic acids and esters is hydrolysis of the aluminium alcoxide. [8] Esters (and amides) are more easily reduced than the parent carboxylic acids. Their reduction affords alcohols and amines, respectively. [9] The idealized equation for the reduction of an ester by lithium aluminium hydride is:
The primary advantages of Fischer esterification compared to other esterification processes are based on its relative simplicity. Straightforward acidic conditions can be used if acid-sensitive functional groups are not an issue; sulfuric acid can be used; weaker acids can be used with a tradeoff of longer reaction times.
J. Thiele and F. Günther first reported a 6-step preparation in 1906. [7] The substance did not receive interest until its potential as a dehydrogenation agent was discovered. A single-step chlorination from 2,3-dicyanohydroquinone was reported in 1965. [8]
The process can tolerate water in the feedstock, free fatty acids are converted to methyl esters instead of soap, so a wide variety of feedstocks can be used. Also the catalyst removal step is eliminated. [9] High temperatures and pressures are required, but energy costs of production are similar or less than catalytic production routes. [10]
Alcohol oxidation is a collection of oxidation reactions in organic chemistry that convert alcohols to aldehydes, ketones, carboxylic acids, and esters. The reaction mainly applies to primary and secondary alcohols. Secondary alcohols form ketones, while primary alcohols form aldehydes or carboxylic acids. [1] A variety of oxidants can be used.