Esterification is a reaction that joins a carboxylic acid and an alcohol to form an ester and water. Esters are important because many have pleasant smells and are found in foods, fragrances, fats, oils, and many polymers. Fischer esterification is one of the most common laboratory methods for making esters.
It shows how acid catalysis and equilibrium control the amount of product formed.
Key Facts
- General reaction: RCOOH + R'OH ⇌ RCOOR' + H2O
- Fischer esterification is acid catalyzed, often using H2SO4 or HCl as the acid catalyst.
- The reaction is reversible, so ester hydrolysis can form the carboxylic acid and alcohol again.
- Removing water or using excess alcohol shifts the equilibrium toward ester formation.
- The acid catalyst is regenerated, so it speeds the reaction without being consumed overall.
- For acetic acid and ethanol: CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O
Vocabulary
- Ester
- An ester is an organic compound with the functional group RCOOR' formed from a carboxylic acid and an alcohol.
- Carboxylic acid
- A carboxylic acid is an organic compound containing the COOH functional group.
- Alcohol
- An alcohol is an organic compound containing an OH group bonded to a carbon atom.
- Acid catalyst
- An acid catalyst provides H+ to speed up a reaction and is regenerated by the end of the mechanism.
- Equilibrium
- Equilibrium is the state in which the forward and reverse reactions occur at equal rates.
Common Mistakes to Avoid
- Forgetting that Fischer esterification is reversible is wrong because the reaction reaches equilibrium and may not go to completion.
- Treating the acid catalyst as a reactant is wrong because H+ is regenerated and does not appear in the overall balanced equation.
- Removing the wrong product is wrong because removing water shifts the equilibrium toward ester formation, while adding water favors hydrolysis.
- Naming the ester in the wrong order is wrong because the alcohol part is named first as an alkyl group, followed by the acid part as a carboxylate.
Practice Questions
- 1 Methanoic acid reacts with methanol to form methyl methanoate and water. If 0.50 mol of methanoic acid reacts completely, how many moles of ester can form?
- 2 A student mixes 0.20 mol of acetic acid with 0.50 mol of ethanol. Assuming the reaction goes to completion based on the limiting reactant, how many moles of ethyl acetate can form?
- 3 In a Fischer esterification mixture at equilibrium, explain why adding excess alcohol or removing water increases the amount of ester produced.