Acid Chlorides

For those of you who are currently revising for the C4 Exam here are some extra notes to keep you going over the final weekend…

Acid Chlorides are a group of chemicals with the functional group -COCl Physical Properties

  • The smaller acid chlorides are colourless liquids with pungent odours
  • They fume in moist air as they hydrolyse to their corresponding Hydro-Halo Acid and

-COCl + H2O –> –COOH + HCl

General Reactions

The main reactions are with Water, Ammonia and primary Amines

R-CO-X + HY –> R-CO-Y + HX

This process is known as Acylation

Acid Chlorides are generally more reactive that their corresponding Carboxylic Acids as the Carbon is polarised further by the proximity of the Halogen increasing the δ+ on the already electron deficient carbon, this makes it even more susceptible to nucleophilic attack.

In the same way Acid Chlorides are more reactive than their similar halogenoalkanes as the very electronegative oxygen also increases the δ+

The rate of reaction depends on several factors (check out this page at for more info) but one other issue is steric hindrance. As acid chlorides are planar molecules neucleophiles are able to approach the δ+ Carbon much more easily than the tetrahedral halogenoalkane. This potentially increases the rate of reaction.

Points you need to know…

Acid Chlorides = -R-COCl
Main reaction = Nucleophilic substitution.
Reactivity = More reactive than Carboxylic acids and Halogenoalkanes