Hydrolyse an acyl chloride with water
Add water at room temperature to an acyl chloride to form the corresponding carboxylic acid and HCl.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 33. Focus on the named compounds, reagents and conditions in each outcome; apply the specified reaction type rather than extending it to unlisted cases. Written practice is self-checked
Before you begin
- Recall carboxylic acids, esters, phenols, alcohols, halogenoalkanes and electrophilic/nucleophilic reaction ideas from earlier topics.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What forms when an acyl chloride reacts with water?
What you will learn
- Recall the room-temperature hydrolysis of acyl chlorides
- Identify the corresponding carboxylic acid product
- Account for HCl formation
Water replaces chlorine
Acyl chlorides hydrolyse rapidly when water is added at room temperature: RCOCl + H₂O → RCOOH + HCl.
The acyl carbon and its R group stay together. The carbonyl remains, while the chlorine is replaced by –OH to regenerate the carboxylic acid.
Use the conditions given
The syllabus specifies addition of water at room temperature. Acyl chlorides are moisture-sensitive and hydrolyse readily.
Do not confuse this with hydrolysis of an alkyl chloride, which proceeds by nucleophilic substitution at a saturated carbon and is much less rapid.
Pause and explain
What happens to the C–Cl bond during acyl-chloride hydrolysis?
Worked example
Predict the products when propanoyl chloride reacts with water at room temperature.
Show the worked solution
- Keep the three-carbon acyl skeleton.
- Replace the chlorine with OH.
- Include HCl.
Answer CH₃CH₂COCl + H₂O → CH₃CH₂COOH + HCl.
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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.
Complete the hydrolysis of CH₃CH₂COCl.
Give me a hint
Replace the acyl chlorine with OH and account for HCl.
Compare my reasoning
- The product keeps the propanoyl carbon skeleton.
- Form CH₃CH₂COOH.
- Include HCl as the other product.
CH₃CH₂COCl + H₂O → CH₃CH₂COOH + HCl.
Look for these in your work
- Acid structure
- Carbon skeleton
- HCl included
State the reagent condition for hydrolysing an acyl chloride in this syllabus outcome.
Give me a hint
Read the specified addition and temperature.
Compare my reasoning
- Add water.
- Use room temperature.
- Name the acid and HCl products.
Add water at room temperature; the acyl chloride forms a carboxylic acid and HCl.
Look for these in your work
- Water stated
- Room temperature
- Products named
A learner predicts propan-1-ol from propanoyl chloride and water. Correct the functional-group change.
Give me a hint
Water converts an acyl chloride to an acid, not an alcohol.
Compare my reasoning
- The carbonyl remains present.
- Chlorine is replaced by hydroxyl at the acyl carbon.
- The product is propanoic acid.
Hydrolysis forms propanoic acid, CH₃CH₂COOH, plus HCl; it does not reduce the carbonyl to an alcohol.
Look for these in your work
- Carbonyl retained
- Product class corrected
- By-product included
Common mistakes
- Naming an alcohol as the organic product
- Removing the carbonyl oxygen
- Omitting HCl
- Adding heat when the stated condition is room temperature
What can you explain now?
What forms when an acyl chloride reacts with water?
Compare with the explanation
A carboxylic acid and HCl
Water replaces the acyl chlorine with OH.
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Make it stick
What are the product and conditions for acyl-chloride hydrolysis?
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.