9701 · 33.3
Acyl chlorides
Acyl chlorides are like super-charged carboxylic acids, ready to donate their acyl group (RCO-) in rapid reactions. Their extreme reactivity makes them incredibly useful building blocks in organic synthesis.
Need to know
What you need to know
- Thionyl chloride ($SOCl_2$) is often preferred as the by-products ($SO_2$ and $HCl$) are gases and can be easily removed, simplifying the purification of the liquid acyl chloride.
- Using $PCl_5$ results in a liquid by-product, phosphorus(III) oxychloride ($POCl_3$), which has a similar boiling point to many acyl chlorides, making separation by distillation more difficult.
Explanation
Acyl Chlorides: The Reactive Acylators
- RCOCl — reactive carbonyl derivative; fumes in air (HCl).
- Reactions: with alcohols → esters; with amines → amides; with arenes → ketones.
- Mechanism: nucleophilic addition–elimination at C=O.
- More reactive than carboxylic acids or esters.