Acyl chlorides

What are acyl chlorides also known as?

Acid chlorides

How are acyl chlorides prepared?

Carboxylic acids area chlorinated with SOCl₂ (thionyl chloride / sulfur dichloride oxide)

Give the general reaction for the production of acyl chlorides

Carboxylic acid + SOCl₂ → Acyl chloride + SO_{2 (g)} + HCl_(g)

What should be remembered about the preparation of acyl chlorides regarding safety?

The reaction should be carried out in a fume cupboard as the products are harmful

Show the preparation of propanoyl chloride from propanoic acid

Give the conditions for reacting acyl chlorides with alcohols

Cold and anhydrous

How should acyl chlorides be named?

1. Remove ‘-ic acid’ from carboxylic acid and replace with ‘-yl’

2. Follow with halogen with -ide ending

Name the structure

Butanoyl bromide

Name the structure

2-methyl butanoyl chloride

What are the 4 physical properties of acyl chlorides

• Form colourless liquids

• Have a pungent odour

• Creates fumes in moist air

• Are readily hydrolysed to form a carboxylic acid and halogen acid

An acyl chloride like ethanoyl chloride is a colourless fuming liquid. Explain its properties

• The strong smell is a mixture of vinegar (ethanoic acid) and acrid smell of HCl gas

• Smell and fumes due to reactions with water vapour in the air

What is the reactivity of acyl chlorides like and why are they very useful in organic synthesis?

Acyl chlorides are extremely reactive and are more acidic than carboxylic acids

• They are useful because they can easily be converted into carboxylic acid derivatives such as esters and amides, with good yields

Describe the reaction of acyl chlorides with nucleophiles

Acyl chlorides lose their chloride ion whilst retaining the C=O double bond

Summarise the overall reaction of acyl chlorides

Acyl chloride + alcohol

Acyl chloride + alcohol → ester + HCl

Show the formation of propyl ethanoate from ethanoyl chloride

Acyl chlorides + phenols

Acyl chlorides + phenols → esters + HCl

Why are acyl chlorides and acid anhydrides better than carboxylic acids when reacting with phenols?

Carboxylic acids are not reactive enough to form esters with phenols

• Acyl chlorides and acid anhydrides are more reactive and don’t need acid catalysts

Give the advantage of making esters with acyl chlorides and alcohol rather than carboxylic acid and alcohol

Esterification through an alcohol and carboxylic acid is reversible and has a low yield

• Alcohols will readily react with acyl chlorides to produce esters

  • The yield is much higher and the reaction is not reversible

Show the formation of phenyl ethanoate

Acyl chloride + water

Acyl chloride + water → carboxylic acid + HCl

Explain the reaction of acyl chlorides with water

When water is added to an acyl chloride, a violent reaction takes place and dense steamy hydrogen chloride fumes are formed

• A carboxylic acid is formed

Show the reaction of acyl chlorides with water

Acyl chlorides + ammonia

Acyl chlorides + ammonia → primary amide + ammonium salt

Acyl chloride + amine

Acyl chloride + amine → secondary amide + ammonium salt

What happens when ammonia and amines react with acyl chlorides?

Ammonia and amines act as nucleophiles by donating the lone pair of electrons on the N atom to an electron deficient species

Show the reaction of ethanoyl chloride and ammonia

Show the reaction of ethanoyl chloride and methylamine

When do acid anhydrides become useful?

Acid anhydrides are less reactive than acyl chlorides and are useful for some laboratory preparations where acyl chlorides may be too reactive

Give the equation for formation of phenyl ethanoate from ethanoic anhydride