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Carbonyls Carboxylic Acids And Derivatives

Learn and apply Carbonyls Carboxylic Acids And Derivatives in the published Chemistry course sequence.

  • GCE A-Level H1 Chemistry 8873-2027
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H1 Carbonyls, Carboxylic Acids and Derivatives: Orientation

Functional-group conversions are safest when you preserve the carbon skeleton first, then decide whether the change is oxidation, reduction, acid–base reaction, condensation or hydrolysis.

H1 8873 scope
  • Apply the specified reactions of aldehydes, ketones, carboxylic acids, esters, amines and amides with their essential conditions.
  • Track products in acidic and alkaline hydrolysis and plan short synthesis routes.
  • Nucleophilic-addition mechanisms, wider carbonyl-test depth, acyl-chloride breadth and H2 nitrogen-derivative extensions are not required.

Definitions (Must Know)

  • An aldehyde contains a terminal carbonyl group, -CHO.
  • A ketone contains a carbonyl group bonded to two carbon groups.
  • A carboxylic acid contains the -CO₂H group.
  • An ester contains the -CO₂- link and forms by condensation of a carboxylic acid with an alcohol.
  • An amine is a nitrogen base derived conceptually from ammonia by replacing hydrogen atoms with carbon groups.
  • An amide contains the -CONH₂ or substituted -CONH⁻ group.
  • Condensation joins molecules with loss of a small molecule; hydrolysis cleaves a bond using water.

Detailed Explanations

A. Carbonyl redox changes

An aldehyde oxidises with acidified K₂Cr₂O₇ or acidified KMnO₄ and heat to a carboxylic acid with the same number of carbon atoms. LiAlH₄, or H₂ with a nickel catalyst, reduces an aldehyde to a primary alcohol and a ketone to a secondary alcohol. Use the product class to work backwards as well as forwards.

B. Carboxylic-acid reactions

Carboxylic acids neutralise alkalis to form carboxylate salts and water, and react with carbonates to form a salt, water and carbon dioxide. The gas observation is therefore evidence of acidic behaviour.

C. Ester formation and hydrolysis

Esterification is a reversible condensation between a carboxylic acid and an alcohol using concentrated H₂SO₄ catalyst and heat. Acidic hydrolysis reverses this change. Alkaline hydrolysis forms an alcohol and a carboxylate salt, so state the salt rather than the free acid.

D. Amines and amides

The nitrogen lone pair lets an amine accept a proton, so ethylamine forms ethylammonium salts with aqueous acids. Ethanoic acid reacts with ethylamine in the presence of dicyclohexylcarbodiimide (DCC) to form N-ethylethanamide; the structure of DCC is not required. Amides hydrolyse on heating with aqueous acid or alkali, and product charge depends on the medium.

E. Multi-step synthesis

Annotate every arrow with the functional-group change before choosing reagents. For example, propanal can be reduced with LiAlH₄ or H₂/Ni to propan-1-ol, or oxidised with acidified K₂Cr₂O₇ or KMnO₄ and heat to propanoic acid; the same three-carbon skeleton is retained.

Worked Examples

Modelled example 1

Deduce a Carbonyl from Two Conversions

Core

Problem

Compound X, C₃H₆O, oxidises to propanoic acid and reduces to propan-1-ol. Identify X.
Study the worked solution

  1. Use the oxidation product

    Method

    Work backwards from propanoic acid to a three-carbon aldehyde.

    Reason

    Oxidation with acidified K₂Cr₂O₇ or KMnO₄ and heat converts an aldehyde to the corresponding carboxylic acid without changing the carbon skeleton.

    Working

    Propanoic acid points to propanal.

  2. Check against the reduction product

    Method

    Reduce the proposed aldehyde with LiAlH₄, or H₂ with a nickel catalyst, to a primary alcohol.

    Reason

    Aldehyde reduction gives the corresponding primary alcohol.

    Working

    CH₃CH₂CHO → [LiAlH₄ or H₂/Ni] CH₃CH₂CH₂OH.

  3. Confirm identity

    Method

    Identify X as propanal.

    Reason

    Propanal satisfies both conversions and retains the three-carbon skeleton.

    Working

    X = CH₃CH₂CHO.

Guided practice 2

React Ethanoic Acid with Carbonate

About 6 min

Problem

Ethanoic acid is added to aqueous sodium carbonate. State the observation and complete the product set.

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Observation
Gas formed

Hints

Hint 1: product pattern
An acid plus carbonate forms a salt, water and a gas.
Hint 2: balance acids
Carbonate accepts two acidic protons, so use two ethanoic-acid molecules.
View solution step by step

  1. Name the products

    Method

    Form sodium ethanoate, water and carbon dioxide.

    Reason

    The acid neutralises carbonate while carbonic acid decomposes to water and carbon dioxide.

    Working

    salt + H₂O + CO₂.

  2. Balance and connect evidence

    Method

    Use two acid molecules per carbonate and state effervescence.

    Reason

    The balanced equation accounts for both sodium ions and the evolved gas.

    Working

    2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.

Guided practice 3

Form Ethyl Ethanoate

About 5 min

Problem

Ethanoic acid reacts with ethanol. State the catalyst and condition, name the organic product and write the equation.

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Catalyst
Organic product

Hints

Hint 1: reaction type
An acid and an alcohol form an ester in a reversible condensation reaction.
Hint 2: naming
Name the alkyl group from the alcohol first, then the carboxylate part from the acid.
View solution step by step

  1. Choose the conditions

    Method

    Heat with concentrated H₂SO₄ catalyst.

    Reason

    These conditions catalyse the reversible condensation between the acid and alcohol.

    Working

    concentrated H₂SO₄, heat.

  2. Build and name the ester

    Method

    Join the ethyl group from ethanol to the ethanoate part from ethanoic acid and include water.

    Reason

    Condensation forms one ester molecule and removes the elements of water.

    Working

    CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O; ethyl ethanoate.

Guided practice 4

Form an Ammonium Salt from an Amine

About 5 min

Problem

Ethylamine reacts with aqueous hydrochloric acid. Write the equation and name the organic salt.

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Ethylamine role
Cation formed

Hints

Hint 1: proton transfer
Add one proton to the nitrogen lone pair.
Hint 2: counter-ion
Chloride remains as the counter-ion of the ammonium salt.
View solution step by step

  1. Show proton acceptance

    Method

    Protonate ethylamine at nitrogen.

    Reason

    The available nitrogen lone pair accepts H⁺.

    Working

    CH₃CH₂NH₂ + H⁺ → CH₃CH₂NH₃ +.

  2. Write and name the salt

    Method

    Include chloride and name ethylammonium chloride.

    Reason

    Hydrochloric acid supplies both the proton and chloride counter-ion.

    Working

    CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃ + Cl⁻; ethylammonium chloride.

Common misconception 5

Use the Hydrolysis Medium

Find and correct the mistake

Learner claim

A learner says heating ethyl ethanoate with aqueous sodium hydroxide produces ethanol and ethanoic acid. Correct the acid-derived product and explain why.

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Alcohol product
Acid-derived product

View solution step by step

  1. Split the ester

    Method

    Form ethanol from the alcohol-derived part and ethanoate from the acid-derived part.

    Reason

    Hydrolysis cleaves the ester link while retaining both carbon skeletons.

    Working

    ethyl ethanoate → ethanol + ethanoate.

  2. Apply the medium

    Method

    State sodium ethanoate, not ethanoic acid, in aqueous sodium hydroxide.

    Reason

    Alkaline conditions deprotonate the acid-derived product.

    Working

    CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH.

Examiner practice 6

Apply Amide Formation and Hydrolysis

4 marks

Examination question

State the reagent used when ethanoic acid reacts with ethylamine to form N-ethylethanamide and write the organic transformation. Then write the equation for heating ethanamide with aqueous sodium hydroxide. [4 marks]

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View solution step by step

  1. Form the substituted amide

    2 marks

    Method

    Use dicyclohexylcarbodiimide (DCC) to join ethanoic acid and ethylamine.

    Reason

    DCC is the required coupling reagent; its structure and DCC-derived by-product are not required.

    Working

    CH₃COOH + CH₃CH₂NH₂ → [DCC] CH₃CONHCH₂CH₃.

  2. Write alkaline hydrolysis

    2 marks

    Method

    Form sodium ethanoate and ammonia on heating ethanamide with aqueous sodium hydroxide.

    Reason

    Hydrolysis cleaves the amide; alkaline medium leaves the acid-derived product as a carboxylate salt.

    Working

    CH₃CONH₂ + NaOH → [heat] CH₃COONa + NH₃.

Challenge 7

Recover the Free Acid after Alkaline Hydrolysis

Minimal support

Medium-change transfer

Ethyl ethanoate is heated with aqueous sodium hydroxide. The mixture is then acidified with dilute hydrochloric acid. State the organic species after hydrolysis and the final organic species after acidification.

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After alkaline hydrolysis
After acidification

Hints

Hint 1: first medium
Hydroxide leaves the acid-derived fragment deprotonated.
Hint 2: second step
Acidification adds a proton to the carboxylate ion; it does not automatically remake the ester.
View solution step by step

  1. Apply alkaline hydrolysis

    Method

    Form ethanol and sodium ethanoate.

    Reason

    Hydroxide hydrolyses the ester and maintains the carboxylate form.

    Working

    CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH.

  2. Apply acidification

    Method

    Protonate ethanoate to ethanoic acid while ethanol remains unchanged.

    Reason

    The medium change alters the charge state of the acid-derived fragment.

    Working

    CH₃COO⁻ + H⁺ → CH₃COOH; final organics: ethanol and ethanoic acid.

Mind Stretchers

Attempt each task before opening its hint.

Mind stretcher 1: Planning a branch from one aldehydeExtension

Question. Starting from propanal, design separate one-step routes to propan-1-ol and propanoic acid. State the reaction type and reagent class for each.

Show Hint

The two arrows move the carbonyl carbon in opposite redox directions.

Show Answer

Reduce propanal with LiAlH₄, or H₂ with a nickel catalyst, to propan-1-ol. Oxidise a separate sample with acidified K₂Cr₂O₇ or KMnO₄ and heat to propanoic acid. Both routes retain the three-carbon skeleton.

Mind stretcher 2: Using charge to identify hydrolysis conditionsExtension

Question. An ester hydrolysis mixture contains ethanol and ethanoate ions rather than ethanoic acid. Deduce the reaction medium and explain the evidence.

Show Hint

Ask which medium removes the acidic proton from a carboxylic acid.

Show Answer

The hydrolysis was alkaline. Hydroxide hydrolyses the ester and deprotonates the acid-derived product, so ethanoate ions—or a named ethanoate salt—remain in the mixture.