SolutionsEster Formation
1. Fischer esterification
Write the product of the reaction of benzoic acid with an excess of methanol in the presence of a catalytic amount of H2SO4. How can the equilibrium be shifted towards the ester?
Methyl benzoate, C6H5COOCH3, and water.
It is shifted by using the alcohol in excess (as the solvent) or by removing the water as it forms (for example, with a Dean-Stark apparatus).
2. Where does the oxygen come from?
If the esterification of acetic acid is carried out with 18O-labelled methanol (CH318OH), where does the isotope end up: in the ester or in the water?
In the ester (CH3CO–18OCH3). The alcohol oxygen attacks the carbonyl carbon and stays in the product; the water eliminated comes from the OH of the acid. This shows that the C–OH bond of the acid is broken, not the O–CH3 bond of the alcohol.