Plan a route through a carboxylic acid and ester
Connect alcohol, carboxylic acid and ester transformations using syllabus conditions and reverse reactions carefully.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 36. Routes use reactions listed in the syllabus and state the relevant reagents and conditions. Check every intermediate and possible by-product; no route implies a practical procedure. Written practice is self-checked
Before you begin
- Use the functional-group reactions from Topics 13–19 and 29–35, including their reagents, conditions, products and limitations.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which condition helps oxidise a primary alcohol fully to a carboxylic acid?
What you will learn
- Plan routes to acids and esters
- Choose esterification or hydrolysis conditions
- Track reversibility and by-products
Form acids and esters
A primary alcohol or aldehyde can be oxidised with acidified dichromate(VI) or manganate(VII) to a carboxylic acid using reflux. A carboxylic acid reacts with an alcohol using concentrated H₂SO₄ as catalyst to form an ester and water.
The carboxylic acid and ester interconvert by hydrolysis. Dilute acid and heat hydrolyse the ester; dilute alkali and heat form a carboxylate, followed by acidification if the target is the acid.
Keep the route reversible only when conditions support it
Esterification is an equilibrium reaction, so name the acid catalyst and do not describe it as automatically complete. Hydrolysis requires the stated dilute acid or alkali and heat.
When planning a route, draw the ester group and identify which side comes from the alcohol and which from the acid. This catches errors in ester names and in the position of oxygen atoms.
Pause and explain
What extra step is needed after alkaline ester hydrolysis if the target is a carboxylic acid?
Worked example
Plan the conversion ethanol → ethanoic acid → ethyl ethanoate.
Show the worked solution
- Oxidise ethanol under reflux to the acid.
- React ethanoic acid with ethanol.
- Use concentrated sulfuric acid as catalyst and account for water.
Answer Ethanol → ethanoic acid by oxidation under reflux; ethanoic acid + ethanol ⇌ ethyl ethanoate + H₂O using concentrated H₂SO₄ as catalyst.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write a route from propan-1-ol to propyl propanoate, identifying the acid and alcohol used in the final step.
Give me a hint
Oxidise a portion of the alcohol to the matching acid, then esterify with the alcohol.
Compare my reasoning
- Reflux propan-1-ol with acidified oxidising agent to make propanoic acid.
- React propanoic acid with propan-1-ol.
- Use concentrated H₂SO₄ as catalyst; water is formed.
Propan-1-ol → propanoic acid; propanoic acid + propan-1-ol ⇌ propyl propanoate + H₂O with concentrated H₂SO₄ catalyst.
Look for these in your work
- Oxidation condition
- Correct ester components
- Catalyst and by-product
A route uses dilute NaOH and heat to hydrolyse ethyl ethanoate. What product form appears before any acidification?
Give me a hint
Follow the alkaline condition rather than the acidic hydrolysis route.
Compare my reasoning
- The ester bond is hydrolysed.
- The ethanoate group is deprotonated in alkali.
- Sodium ethanoate, not ethanoic acid, is formed initially.
Sodium ethanoate (a carboxylate salt) forms before acidification.
Look for these in your work
- Alkaline condition applied
- Carboxylate named
- Acid distinguished
A proposed esterification product swaps the alkyl and acid-derived portions. How can the reactants identify the correct name and structure?
Give me a hint
The alcohol contributes the group attached through the ester oxygen.
Compare my reasoning
- Name the alcohol-derived alkyl group first.
- The carboxylic acid contributes the alkanoate part.
- Join them through –COO– with water formed.
The ester name is alcohol-derived alkyl followed by the acid-derived alkanoate; draw the alkyl group bonded through oxygen and retain the acid carbonyl.
Look for these in your work
- Alcohol contribution identified
- Acid contribution identified
- Link and name corrected
Common mistakes
- Distilling an aldehyde when the target is the acid
- Calling an ester hydrolysis an esterification
- Leaving out concentrated H₂SO₄ in esterification
- Writing acid as the product of alkaline hydrolysis without acidification
What can you explain now?
Which condition helps oxidise a primary alcohol fully to a carboxylic acid?
Compare with the explanation
Reflux with acidified oxidising agent
Reflux supports continued oxidation to the acid.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do oxidation, esterification and hydrolysis connect in a route through carboxylic acids and esters?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.