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8873 / 2027
Polymers and Organic Chemistry

Lesson 7 of 12

Condensation and hydrolysis

The functional group and reaction medium determine the products.

A-Level 8873, revised syllabus (2026-2027)

  • I can use organic reaction terminology.Syllabus

    Syllabus 8873, 9(b). Use organic reaction terminology.

  • I can apply the specified organic reactions, conditions and analogous product predictions.Syllabus

    Syllabus 8873, 9(g). Apply the specified organic reactions, conditions and analogous product predictions.

Make and break ester or amide links

The functional group and reaction medium determine the products.

Condensation joins molecules and removes a small molecule, often water. Hydrolysis uses water to break a bond. Heating with aqueous acid or alkali speeds it up. Ester links join a carbonyl group to O, and amide links join it to N. Find that linking bond before you try to name the products.

Two ways ethanoic acid makes a new covalent link
Link formedReagents and conditionsOrganic product
Ester, -C(=O)-O-Ethanoic acid + ethanol; concentrated H2SO4 catalyst, heat.CH3COOH + HOCH2CH3 ⇌ CH3COOCH2CH3 + H2O
Amide, -CONH-Ethanoic acid + ethylamine in the presence of DCC (dicyclohexylcarbodiimide).CH3CONHCH2CH3, N-ethylethanamide. The acid-derived fragment remains attached to the carbonyl carbon; the ethyl group remains on nitrogen.

The ester link -C(=O)-O- is neutral. The dash at the end is a covalent bond to the next carbon group. In a carboxylate ion, -COO-, the minus sign is a charge. These are different structures. So the ester links in a polyester do not give the polymer a negative charge.

Keep the two fragments attached to the right atoms

Structural fragments show the carbonyl carbon joined to oxygen in an ester and to nitrogen in an amide. Hydrolysis cleaves the acyl C-O or acyl C-N bond, restoring an acid-derived fragment and an alcohol- or amine-derived fragment. The diagram is a connectivity guide, not a reaction mechanism.

Track fragments rather than splitting a name. The ethyl group is attached through oxygen in the ester and through nitrogen in the amide.
Ethyl ethanoate hydrolysis: the medium changes the acid product
ConditionsEquationWhy this form appears
Aqueous acid and heatCH3COOCH2CH3 + H2O ⇌ CH3COOH + CH3CH2OHThe acidic mixture contains the carboxylic acid. Acid catalyses the reaction.
Aqueous NaOH and heatCH3COOCH2CH3 + NaOH → CH3COONa + CH3CH2OHAny acid formed is deprotonated by the alkali. The isolated acid-derived product in this medium is the carboxylate salt.
Ethanamide hydrolysis: include the nitrogen product
ConditionsNet ionic equationProduct check
Aqueous acid and heatCH3CONH2 + H2O + H+ → CH3COOH + NH4+The nitrogen product is protonated in acid; write ammonium, not free ammonia as the final major form.
Aqueous alkali and heatCH3CONH2 + OH- → CH3COO- + NH3The acid fragment is a carboxylate; nitrogen leaves as ammonia. With NaOH, the salt is sodium ethanoate.

Worked exampleTransfer hydrolysis to an unfamiliar ester

Predict the organic products when methyl propanoate, CH3CH2COOCH3, is heated with aqueous NaOH.

Try it first. Then show the worked stepsHide the worked steps
  1. Identify the acid-derived fragment CH3CH2CO- and the O-attached methyl fragment.
  2. Breaking the ester link gives a propanoate ion and methanol in the alkaline mixture.
  3. Include Na+ as counter-ion: CH3CH2COOCH3 + NaOH → CH3CH2COONa + CH3OH. All four carbons are accounted for.
Answer

Sodium propanoate and methanol form. Propanoic acid would require subsequent acidification.

Separating the product is about reasoning, not a memorised list of apparatus. After making an ester, ask what else is left: excess acid, acid catalyst, alcohol and water may all be present. Washing with water removes impurities that dissolve in water. Washing with a carbonate solution neutralises acid. If two liquid layers form, separate the layer that holds the ester, then dry it to remove the last water. Use the solubility and boiling-point data given to choose further steps. Never decide which layer is which only from whether it is on top.

Check your understanding

CH3CONHCH2CH3 is heated with aqueous acid. What are the organic products?

  1. Ethanoic acid and ethanol, CH3CH2OH
  2. Ethanoic acid and ethylammonium ions, CH3CH2NH3+
  3. Ethanamide and ethane, CH3CONH2 and CH3CH3
Show the answer

Ethanoic acid and ethylammonium ions, CH3CH2NH3+

Hydrolysis breaks the amide link. The ethyl group stays on nitrogen, and the acid protonates the ethylamine released.