Acyl Chlorides & Acylation

Chemistry: Cambridge International A Level, topic 3.4.6

Formation of Acyl Chlorides

Acyl chlorides can be produced by reacting carboxylic acids with an inorganic compound called thionyl chloride (sulphur dichloride oxide).

Acyl chlorides are produced from a reaction between sulphur dichloride oxide (SOCl₂) and a carboxylic acid.
Hydrogen chloride and sulphur dioxide gases are produced in the reaction.

Fractional distillation can be used to remove excess reagents from the acyl chloride.
Hydrogen chloride and sulphur dioxide are given off as gases.

Acylation reactions can be used to produce a variety of organic compounds, like amides.

The nucleophilic addition-elimination reaction happens with acyl chlorides and acid anhydrides.
It is used to produce amides, carboxylic acids, and esters.
An example is the production of ethyl ethanoate from ethanoyl chloride (an acyl chloride) with ethanol.
Ethanoyl chloride reacts with cold ethanol in a highly exothermic reaction. HCl is evolved as a gas and ethyl ethanoate is produced:
The overall reaction and mechanism is shown on the next slide.

Another example of such a reaction is the production of phenyl benzoate.
Phenol (C₆H₅OH) reacts with benzoyl chloride (C₆H₅COCl) in the presence of NaOH and heat to produce phenyl benzoate.
The equation for this reaction is shown below:
C₆H₅OH + C₆H₅COCl → C₆H₅COOC₆H₅ + HCl

Acyl chlorides are produced by reacting sulphur dichloride oxide and a carboxylic acid.
What gases are produced as by-products in the reaction?
Which of these are true about the formation of acyl chlorides?
In the mechanism of acyl chloride to an ester, what is removed?