What is esterification? Give its mechanism. Also give reactivity order of alchols and acids towards esterification
Answers
Description: When a carboxylic acid is treated with an alcohol and an acid catalyst, an ester is formed (along with water). This reaction is called the Fischer esterification.
Notes: The reaction is actually an equilibrium. The alcohol is generally used as solvent so is present in large excess. Many different acids can be used; it’s common to see just “H+”, although H2SO4 (sulfuric acid) and TsOH (tosic acid) are also often used.
When a carboxylic acid is treated with an alcohol and an acid catalyst, an ester is formed along with water. This reaction is called the Fischer esterification.
Mechanism: Interestingly, such simple reaction (replacement of OH by OR) there are actually a lot of steps. Protonation of the carbonyl oxygen by acid makes the carbonyl carbon a much better electrophile. It undergoes 1,2-addition by the alcohol whereupon the proton from the alcohol is transferred to one of the OH groups. Subsequent 1,2-elimination of water leads to the protonated ester, and the ester is then deprotonated.
The order of reactivity of alcohols is Tertiary< secondary< Primary alcohol.