Alcohols: acyl chlorides form esters
· Alcohol + acyl chloride → ester + hydrogen chloride.
· General equation: RCOCl + R′OH → RCOOR′ + HCl.
· This is an esterification reaction involving an acyl chloride and an alcohol.
· The alcohol provides the alkoxy group, –OR′, in the ester.
· The acyl chloride provides the acyl group, RCO–, in the ester.
· Key observation: misty fumes of HCl may be produced.
· The reaction is usually rapid because acyl chlorides are very reactive.
Acyl chlorides contain the –COCl functional group. In this topic, the chlorine is replaced by an alkoxy group from an alcohol to form an ester. Source
Required example: ethyl ethanoate
· Required CIE example: formation of ethyl ethanoate.
· Reactants: ethanoyl chloride + ethanol.
· Word equation: ethanoyl chloride + ethanol → ethyl ethanoate + hydrogen chloride.
· Structural equation: CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl.
· Product ester: ethyl ethanoate, also called ethyl acetate.
· Naming tip: ethyl comes from the alcohol part, ethanoate comes from the acyl chloride part.
· Common exam trap: do not name the ester as “ethanol ethanoate”; use alkyl alkanoate format.
Ethyl ethanoate has the ester linkage –COO–. The CH₃CO– part comes from ethanoyl chloride, while the –OCH₂CH₃ part comes from ethanol. Source
How to write the ester product quickly
· Start with the acyl chloride: RCOCl.
· Remove Cl and replace it with OR′ from the alcohol R′OH.
· Product pattern: RCOOR′.
· Example: CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl.
· Always include HCl as the second product.
· Name esters as alkyl alkanoate: alcohol part first, acyl chloride/carboxylate part second.
Reaction type and exam language
· Reaction type: esterification / nucleophilic acyl substitution.
· The alcohol oxygen acts as a nucleophile because it has lone pairs.
· The carbonyl carbon in the acyl chloride is electron-deficient.
· The C–Cl bond is broken and Cl⁻ is replaced by the alcohol-derived –OR′ group.
· For 32.1, focus on being able to describe the reaction, write the equation, and identify/name the ester.
· If a mechanism is requested in a linked acyl chloride question, use addition–elimination language.
The diagram shows how an alcohol reacts with an acyl chloride to form an ester. It is useful for understanding why the reaction is described as addition–elimination in linked acyl chloride questions. Source
Practical and safety points
· Acyl chlorides can release HCl fumes, so reactions should be handled carefully.
· HCl fumes are acidic and can appear as white/misty fumes in moist air.
· The reaction does not require the same reversible equilibrium conditions as carboxylic acid + alcohol esterification.
· In exam answers, state the products clearly: ester + HCl.
· Do not omit the hydrogen chloride product.
This reaction scheme summarises the key 32.1 reaction: acyl chloride + alcohol → ester. It reinforces the exam equation pattern and the formation of HCl as the by-product. Source
Checklist: can you do this?
· Write the general equation RCOCl + R′OH → RCOOR′ + HCl.
· Write the example equation for ethyl ethanoate formation.
· Identify which part of the ester comes from the alcohol and which comes from the acyl chloride.
· Name esters correctly using alkyl alkanoate format.
· State that HCl fumes are formed as a by-product.
Exam traps to avoid
· Do not forget HCl in the products.
· Do not confuse ethyl ethanoate with ethanoic acid or ethanol.
· Do not name the ester from left to right in the displayed formula; use alcohol part first.
· Do not write water as a product; this reaction forms HCl, not H₂O.
· Do not overcomplicate 32.1: the core requirement is the reaction of alcohols with acyl chlorides to form esters.