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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

6.1.3 Carboxylic acids and esters

Acyl chloridesEstersProperties of carboxylic acids

Acyl chlorides

Specification Reference 6.1.3 (e)–(f)

Quick Notes

  • Acyl chlorides are highly reactive compounds with a –COCl functional group.
OCR (A) A-Level Chemistry structure diagram of an acyl chloride functional group –COCl.
  • Acyl chlorides can be formed from carboxylic acids using SOCl2:
    • Carboxylic acid + SOCl2 → acyl chloride + SO2 + HCl
  • Reactions of Acyl Chlorides
    • With alcohols → esters.
    • With water → carboxylic acids.
    • With ammonia → primary amides.
    • With amines → secondary amides.
    • With phenol → esters.

Full Notes

Acyl chlorides are highly reactive derivatives of carboxylic acids and contain a –COCl functional group.

OCR (A) A-Level Chemistry diagram showing acyl chloride functional group structure.

Formation of Acyl Chlorides from Carboxylic Acids

Acyl chlorides are commonly made by replacing the –OH group of a carboxylic acid with a Cl atom using SOCl2:

OCR (A) A-Level Chemistry diagram showing acyl chloride from carboxylic acid using SOCl2.

RCOOH + SOCl2 → RCOCl + SO2 + HCl

This reaction is often used because the by-products are gases and escape, making purification easier.

Reactions of Acyl Chlorides

Acyl chlorides are highly reactive and undergo nucleophilic substitution reactions. You need to know the following reactions:

Reaction with Alcohols

OCR (A) A-Level Chemistry reaction of acyl chloride with alcohol to form an ester and HCl.

RCOCl + R'OH → RCOOR' + HCl
Forms an ester without needing a catalyst (faster and more direct than using carboxylic acids).

Reaction with Water

OCR (A) A-Level Chemistry vigorous reaction of acyl chloride with water producing carboxylic acid and HCl.

RCOCl + H2O → RCOOH + HCl
This is a vigorous reaction; steamy fumes of HCl are released.

Reaction with Ammonia (NH3)

OCR (A) A-Level Chemistry reaction of acyl chloride with ammonia producing primary amide and HCl.

RCOCl + NH3 → RCONH2 + HCl
Forms a primary amide. HCl produced reacts with excess NH3 to form NH4Cl.

Reaction with Primary Amines

OCR (A) A-Level Chemistry reaction of acyl chloride with primary amine producing secondary amide and HCl.

RCOCl + R'NH2 → RCONHR' + HCl

Acyl chlorides can also react with secondary amines to form tertiary amides:
RCOCl + R'2NH → RCONR'2 + HCl

Reaction with Phenol

OCR (A) A-Level Chemistry reaction of acyl chloride with phenol forming an ester and HCl.

RCOCl + PhOH → RCOOPh + HCl

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Matt’s exam tip

Phenol is less reactive than alcohols and can’t readily form an ester with carboxylic acids but can form an ester with acyl chlorides, due to their higher reactivity.

Summary