Nucleophilic Addition / Elimination in the Reaction Between Acyl Chlorides and Alcohols
This page gives you the facts and a simple, uncluttered mechanism for the nucleophilic addition / elimination reaction between acyl chlorides (acid chlorides) and alcohols. 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. Similarly, ethanol is taken as a typical alcohol. If you are interested in another alcohol, you can replace the CH3CH2 group by any other alkyl group.
The Reaction Between Ethanoyl Chloride and Ethanol
Ethanoyl chloride reacts instantly with cold ethanol. There is a very exothermic reaction in which a steamy acidic gas is given off (hydrogen chloride). Ethyl ethanoate (an ester) is formed.
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 an ethanol molecule.
Note: Only one of the two lone pairs on the oxygen in the ethanol 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 ethyl ethanoate and hydrogen chloride.