CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.5.5 Relative Ease of Hydrolysis

Hydrolysis of Acyl Chlorides, Alkyl Chlorides & Halogenoarenes

  • Hydrolysis is the breakdown of a compound using water
  • The ease of hydrolysis for different organic compounds may differ
  • For example, the ease of hydrolysis, starting with the compounds most readily broken down, is: acyl chloride > alkyl chloride > aryl chloride
  • This trend can be explained by looking at the strength of the C-Cl

Strength of C-Cl bond in acyl chlorides

  • Acyl chlorides are hydrolysed most readily at room temperature
  • This is because the carbon bonded to the chlorine atom is also attached to an oxygen atom
  • There are two strong electronegative atoms pulling electrons away from the carbonyl carbon, leaving it very δ+
  • The C-Cl bond is therefore weakened and nucleophilic attack of the carbonyl carbon is much more rapid

Carboxylic Acids & Derivatives - Hydrolysis of Acyl Chlorides, downloadable AS & A Level Chemistry revision notes

The hydrolysis of acyl chlorides occurs most readily

Strength of C-Cl bond in alkyl chlorides

  • The carbonyl carbon in alkyl chlorides is only attached to one electronegative atom which pulls electrons away from it
  • This carbon atom is therefore not very δ+ and the C-Cl bond is stronger than the C-Cl bond in acyl chlorides
  • The hydrolysis of alkyl chlorides, therefore, requires a strong alkali (such as OH) to be refluxed with it
  • An OH ion will hydrolyse the alkyl chloride as it a stronger nucleophile than H2O

Carboxylic Acids _ Derivatives - Hydrolysis of Alkyl Chlorides, downloadable AS & A Level Chemistry revision notes

The hydrolysis of alkyl chlorides requires a strong nucleophile

Strength of C-Cl bond in aryl chlorides

  • In aryl chlorides, the carbon atom bonded to the chlorine atom is part of the delocalised π bonding system of the benzene ring
  • One of the lone pairs of electrons of the Cl atom overlaps with this delocalised system
  • The C-Cl bond, therefore, has some double-bond character causing it to become stronger
  • As a result, the C-Cl bond is difficult to break and hydrolysis will not occur

Carboxylic Acids _ Derivatives - Hydrolysis of Aryl Chlorides, downloadable AS & A Level Chemistry revision notes

Due to the strong C-Cl bond in aryl chlorides, these compounds will not undergo hydrolysis

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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