AQA · A-Level · Chemistry

    Course version: 7405 · Version from Sept 2016

    The industrial advantages of ethanoic anhydride over ethanoyl chloride in…

    Full specification wording

    Acylation (A-level only): The industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of the drug aspirin.

    Aspirin is made by acylating the -OH group of 2-hydroxybenzoic acid; the -COOH on the ring is left alone.

    Checked against the AQA 7405 specification (opens in a new tab) on .

    • Point 3 of 5
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Aspirin is made by acylating the -OH group of 2-hydroxybenzoic acid; the -COOH on the ring is left alone. Either ethanoyl chloride or ethanoic anhydride will do the job, but industry chooses the anhydride. It is cheaper to buy, it is much less readily hydrolysed by moisture in the air so it can be stored and handled safely, and it reacts far less violently with water if there is a spill. The by-product matters just as much: the anhydride releases ethanoic acid, which is a weak acid that can be recovered and reused, while the acyl chloride releases hydrogen chloride, a corrosive and toxic gas that would need scrubbing. Against that, the anhydride has the poorer atom economy of the two.

    What earns the marks

    • The anhydride being cheaper or less corrosive than the acyl chloride.
    • The anhydride reacting less vigorously with water, so it is safer to store and handle.
    • Ethanoic acid rather than hydrogen chloride as the by-product.
    • Identifying the -OH group of 2-hydroxybenzoic acid as the group that is acylated.

    Common mistakes and how to put them right

    • Claiming the anhydride gives the better atom economy, when its larger by-product makes it worse.

    • Saying the -COOH group on the ring is esterified, rather than the -OH group.

    • Describing hydrogen chloride as a useful by-product without any qualification.

    • Arguing the anhydride is chosen because it is more reactive, when the opposite is the point.

    Exam tips

    • Give industrial reasons in pairs: a property and the consequence for a factory, such as 'less easily hydrolysed, so it can be stored'.
    • Name the by-product in every comparison; that is usually where the mark is.

    Try the lesson

    The start of the Acylation (A-level only): The industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of the drug aspirin. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In the industrial manufacture of aspirin, ethanoic anhydride is preferred to ethanoyl chloride mainly because ethanoic anhydride reacts less violently with water. Which additional property of ethanoic anhydride also makes it the safer industrial choice?

    Listen

    Aspirin is made by acylating the -OH group of 2-hydroxybenzoic acid; the -COOH on the ring is left alone. Either ethanoyl chloride or ethanoic anhydride will do the job, but industry chooses the anhydride. It is cheaper to buy, it is much less readily hydrolysed by moisture in the air so it can be stored and handled safely, and it reacts far less violently with water if there is a spill. The by-product matters just as much: the anhydride releases ethanoic acid, which is a weak acid that can be recovered and reused, while the acyl chloride releases hydrogen chloride, a corrosive and toxic gas that would need scrubbing. Against that, the anhydride has the poorer atom economy of the two. A strong answer earns marks for these points. the anhydride being cheaper or less corrosive than the acyl chloride. the anhydride reacting less vigorously with water, so it is safer to store and handle. ethanoic acid rather than hydrogen chloride as the by-product. identifying the -OH group of 2-hydroxybenzoic acid as the group that is acylated. Exam tip: Give industrial reasons in pairs: a property and the consequence for a factory, such as 'less easily hydrolysed, so it can be stored'.

    See it

    A top-down flowchart. At the top, 2-hydroxybenzoic acid leads to a node labelled 'Acylate the -OH group', which leads to Aspirin. From the acylation node two routes branch out: the ethanoyl chloride route, which leads to a by-product of hydrogen chloride described as a corrosive, toxic gas that needs scrubbing; and the ethanoic anhydride route, which leads to a by-product of ethanoic acid described as a weak acid that can be recovered and reused. The ethanoic anhydride route also leads to a node stating it is cheaper, less readily hydrolysed and reacts less violently with water, and to a node stating it has poorer atom economy.
    It compares the two acylation routes to aspirin, showing the by-product and industrial advantages of ethanoic anhydride over ethanoyl chloride.

    Key words

    Say what each word means before you turn the card.

    industrial choice of reagent

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    by-product handling

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    safety and storage

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    atom economy

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    See every definition
    industrial choice of reagent
    Industry chooses ethanoic anhydride over ethanoyl chloride because it is cheaper to buy and much less readily hydrolysed by moisture in the air.
    by-product handling
    The anhydride releases ethanoic acid, a weak acid that can be recovered and reused, while the acyl chloride releases hydrogen chloride, a corrosive and toxic gas that would need scrubbing.
    safety and storage
    The anhydride can be stored and handled safely and reacts far less violently with water if there is a spill.
    atom economy
    The anhydride has the poorer atom economy of the two, because its larger by-product makes it worse.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top, 2-hydroxybenzoic acid leads to a node labelled 'Acylate the -OH group', which leads to Aspirin. From the acylation node two routes branch out: the ethanoyl chloride route, which leads to a by-product of hydrogen chloride described as a corrosive, toxic gas that needs scrubbing; and the ethanoic anhydride route, which leads to a by-product of ethanoic acid described as a weak acid that can be recovered and reused. The ethanoic anhydride route also leads to a node stating it is cheaper, less readily hydrolysed and reacts less violently with water, and to a node stating it has poorer atom economy.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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