Chemistry A2 · Hydroxy compounds. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
An alcohol reacts with an acyl chloride to form an ester and hydrogen chloride. With ethanol and ethanoyl chloride the ester is ethyl ethanoate.
The reaction is fast at room temperature, needs no catalyst and goes to completion. This is better than using a carboxylic acid, which needs heating with concentrated sulfuric acid and only reaches an equilibrium. Steamy fumes of HCl are seen.
The O–H bond of the alcohol breaks: the oxygen of the alcohol joins to the C=O carbon of the acyl chloride, and the chlorine leaves with the hydrogen as HCl. The mechanism is addition–elimination. Everything must be dry, because water also reacts with the acyl chloride.
Giving water as the other product. Water forms when an alcohol reacts with a carboxylic acid; with an acyl chloride the other product is HCl.
Answer: 3.93 g of ethanoyl chloride (3 significant figures); the ester is butyl ethanoate.
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