Acyl chlorides
Cambridge A-Level Chemistry (9701) · Unit 33: Carboxylic acids and derivatives (A Level) · 8 flashcards
Acyl chlorides is topic 33.3 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 33 — Carboxylic acids and derivatives (A Level) , alongside Carboxylic acids and Esters. In one line: Phosphorus trichloride (PCl₃) with heat, phosphorus pentachloride (PCl₅), or thionyl chloride (SOCl₂). These reagents replace the -OH group of the carboxylic acid with a chlorine atom.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 6 definitions and 2 key concepts — covering the precise wording mark schemes reward. Use the 6 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
List three reagents that can be used to convert a carboxylic acid into an acyl chloride
Phosphorus trichloride (PCl₃) with heat, phosphorus pentachloride (PCl₅), or thionyl chloride (SOCl₂). These reagents replace the -OH group of the carboxylic acid with a chlorine atom.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- recall the reactions (reagents and conditions) by which acyl chlorides can be produced: (a) reaction of carboxylic acids with PCl ₃ and heat, PCl ₅ or SOCl ₂
- describe the following reactions of acyl chlorides: (a) hydrolysis on addition of water at room temperature to give the carboxylic acid and HCl (b) reaction with an alcohol at room temperature to produce an ester and HCl (c) reaction with phenol at room temperature to produce an ester and HCl (d) reaction with ammonia at room temperature to produce an amide and HCl (e) reaction with a primary or secondary amine at room temperature to produce an amide and HCl
- describe the addition–elimination mechanism of acyl chlorides in reactions in 33.3.2(a)–(e)
- explain the relative ease of hydrolysis of acyl chlorides, alkyl chlorides and halogenoarenes (aryl chlorides)
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Acyl chlorides
- › Check the question conditions carefully; use 22.4 dm³ per mole for calculations involving gas at s.t.p.
List three reagents that can be used to convert a carboxylic acid into an acyl chloride.
Phosphorus trichloride (PCl₃) with heat, phosphorus pentachloride (PCl₅), or thionyl chloride (SOCl₂). These reagents replace the -OH group of the carboxylic acid with a chlorine atom.
Write the general equation for the reaction of an acyl chloride with water.
RCOCl + H₂O → RCOOH + HCl. This hydrolysis reaction produces a carboxylic acid and hydrogen chloride gas.
What type of organic compound is produced when an acyl chloride reacts with an alcohol?
An ester is formed. The reaction is: RCOCl + R'OH → RCOOR' + HCl. Hydrogen chloride gas is also produced.
Write the general equation for the reaction of an acyl chloride with ammonia.
RCOCl + 2NH₃ → RCONH₂ + NH₄Cl. An amide is formed, along with ammonium chloride.
Describe the addition-elimination mechanism of acyl chloride reactions.
The nucleophile (
Outline the reaction of acyl chloride with phenol.
RCOCl + C₆H₅OH → RCOOC₆H₅ + HCl. An ester is formed, along with hydrogen chloride gas. Phenol is benzene ring with an -OH group.
Explain why acyl chlorides are more readily hydrolysed than alkyl chlorides or halogenoarenes.
The carbonyl carbon in acyl chlorides is more δ+ due to the electronegativity of both the oxygen and chlorine atoms. This makes it more susceptible to nucleophilic attack by water. Alkyl chlorides and halogenoarenes are less polarised and the C-Cl bond is stronger.
Write the general equation for the reaction of an acyl chloride with a primary amine.
RCOCl + 2R'NH₂ → RCONHR' + R'NH₃Cl. An N-substituted amide is formed, along with the amine salt.
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Acyl chlorides sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
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