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Nucleophilic Addition / Elimination in the Reaction Between Acyl chlorides and Water

This page gives you the facts and a simple, uncluttered mechanism for the nucleophilic addition / elimination reaction between acyl chlorides (acid chlorides) and water. If you want the mechanism explained to you in detail, there is a link at the bottom of the page.

Ethanoyl chloride is taken as a typical acyl chloride. Any other acyl chloride will behave in the same way. Simply replace the CH3 group in what follows by anything else you want.

The Reaction Between Ethanoyl chloride and Water

The Facts

Ethanoyl chloride reacts instantly with cold water. There is a very exothermic reaction in which a steamy acidic gas is given off (hydrogen chloride) and ethanoic acid is formed.

The Mechanism

The first stage (the addition stage of the reaction) involves a nucleophilic attack on the fairly positive carbon atom by one of the lone pairs on the oxygen of a water molecule.

Note: Only one of the two lone pairs on the oxygen in water is shown. This is to avoid cluttering an already complicated diagram with things that aren't relevant.

The second stage (the elimination stage) happens in two steps. In the first, the carbon-oxygen double bond reforms and a chloride ion is pushed off.

That is followed by removal of a hydrogen ion by the chloride ion to give ethanoic acid and hydrogen chloride.