1. A carboxylic acid plus an alcohol, with catalytic strong acid, gives an ester and water.
Acetic acid + methanol → methyl acetate (+ water).
2. Only a catalytic amount of acid is needed, because the proton is regenerated at the end.
H2SO4 or HCl activates the carbonyl but is not consumed, so a trace is enough.
3. The mechanism is nucleophilic acyl substitution: protonate, add, proton-transfer, lose water, deprotonate.
Protonating the C=O makes the carbonyl carbon electrophilic; the alcohol adds, and after proton shuffles the OH leaves as water.
4. The reaction is a reversible equilibrium, so excess water and acid run it backward as ester hydrolysis.
Reverse direction: methyl acetate hydrolyzes back to acetic acid + methanol.
5. Drive it toward ester with a large excess of alcohol or by removing water (Le Châtelier).
Benzoic acid + methanol → methyl benzoate, pushed by excess methanol.
6. Summary
Acid + alcohol + catalytic H+ → ester + water · mechanism = nucleophilic acyl substitution · catalyst regenerated · reversible equilibrium · excess alcohol or remove water pushes forward · excess water reverses it (hydrolysis).
Quiz yourself
Tap a question to reveal the answer — free, no login.
A carboxylic acid and an alcohol, with a catalytic amount of strong acid (H2SO4 or HCl). They give an ester plus water — e.g. acetic acid + methanol → methyl acetate.
Because it is a reversible equilibrium, use Le Châtelier: add a large excess of the alcohol, or remove the water as it forms (e.g. distillation or a drying agent). Both shift the reaction forward.
It is nucleophilic acyl substitution: protonate the C=O, the alcohol adds, protons transfer, water leaves, then deprotonation gives the ester. The acid is a catalyst — regenerated in the last step — so a catalytic amount suffices.
Run the reaction in reverse (ester hydrolysis): heat the ester with excess water and acid (H3O+). Le Châtelier now favors the acid + alcohol, giving back acetic acid and methanol.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.