Esterification is the process by which an ester is formed. It is a popular practice among amateur chemists because of the usefulness of some esters (such as ethyl acetate) and for the wide range of smells different esters can produce, such as methyl salicylate (wintergreen).
The Fischer-Speier method of esterification, often simply called a Fischer esterification, is the most well-known method used, and involves producing an ester from an alcohol and a carboxylic acid. Carboxylic acids and alcohols esterify in small amounts according to a reversible equation:
RCOOH + R'OH ⇌ RCOOR' + H2O
The reaction above is catalyzed by a strong acid; the typical acid used is sulfuric acid, but p-toluenesulfonic acid (tosic, tosylic acid) is also sometimes used. In addition, removal of water during the esterification process also serves to drive the equilibrium towards the right. Sulfuric acid is useful in this way too, as it acts as a strong dehydrating agent, sequestering water. The reaction rate is greatly increased as the mixture is heated, leading most Fischer esterifications to be done under reflux. Increased yields can be achieved during this reaction through any of these steps:
- Using anhydrous reagents, as water drives the equation towards the left
- Using a large excess of the alcohol or solvent to reduce the concentration of water
- Using a larger amount of sulfuric acid to sequester water
- Adding an anhydrous desiccant to bind water, such as calcium sulfate.
- Removal of water from the reaction vessel, such as boiling it off(if the alcohol has a higher boiling point than water), or distilling out a low boiling azeotrope of water and the solvent used, such as toluene.