9701 · 33.3
Acyl chlorides flashcards
Revision flashcards for Cambridge 9701 Acyl chlorides (syllabus 33.3). Flip, recall, then mark a real past-paper question.
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What is the functional group of an acyl chloride?
The -COCl group, known as the acyl chloride or acid chloride group.
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How are acyl chlorides named?
Replace the '-oic acid' from the parent carboxylic acid with '-oyl chloride'. For example, ethanoic acid becomes ethanoyl chloride.
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Name a reagent used to convert a carboxylic acid into an acyl chloride.
Thionyl chloride ($SOCl_2$) or phosphorus(V) chloride ($PCl_5$).
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Write the balanced equation for the reaction of ethanoic acid with thionyl chloride.
$CH_3COOH + SOCl_2 \rightarrow CH_3COCl + SO_2(g) + HCl(g)$
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Why is thionyl chloride ($SOCl_2$) often the preferred reagent for synthesising acyl chlorides in the lab?
Because its by-products, sulfur dioxide ($SO_2$) and hydrogen chloride (HCl), are gases, which are easily removed from the liquid product, simplifying purification.
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What is observed when ethanoyl chloride reacts with water?
A vigorous/violent reaction occurs, producing steamy white fumes of hydrogen chloride (HCl) and aqueous ethanoic acid.
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What type of mechanism do acyl chlorides undergo in their characteristic reactions?
Nucleophilic addition-elimination.
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What are the products of the reaction between propanoyl chloride and ethanol?
Ethyl propanoate (an ester) and hydrogen chloride. $CH_3CH_2COCl + CH_3CH_2OH \rightarrow CH_3CH_2COOCH_2CH_3 + HCl$.
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Why is the reaction of an acyl chloride with an alcohol a better method for esterification than using a carboxylic acid?
The reaction is much faster, occurs at room temperature, and is irreversible (goes to completion), leading to a higher yield.
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What are the products when butanoyl chloride reacts with excess ammonia?
Butanamide ($CH_3CH_2CH_2CONH_2$) and ammonium chloride ($NH_4Cl$). Two moles of ammonia are required per mole of acyl chloride.
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What is the product of the reaction between ethanoyl chloride and methylamine ($CH_3NH_2$)?
An N-substituted amide, N-methylethanamide ($CH_3CONHCH_3$), and methylammonium chloride ($CH_3NH_3Cl$).
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Why are acyl chlorides so much more reactive than esters?
The chloride ion ($Cl^−$) is an excellent leaving group as it is the conjugate base of a strong acid (HCl). The ethoxide ion ($CH_3CH_2O^−$) from an ester is a poor leaving group as it is the conjugate base of a weak acid (ethanol).