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Carboxylic Acids and Their Derivatives

Hydroxynitriles, hydrolysis and reduction of nitriles

  • 3 things to know
  • Component 2

Overview

Reagents used to convert an aldehyde into a hydroxynitrile, product formed when ethanal reacts with hydrogen cyanide and product formed when propanone reacts with hydrogen cyanide.

What you need to know

Answer each one before you reveal it.

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Key term

Explain why the hydroxynitrile obtained from ethanal is optically inactive.

Key term

Name the product formed when ethanal reacts with hydrogen cyanide.

Key term

Name the product formed when propanone reacts with hydrogen cyanide.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the reagents used to convert an aldehyde into a hydroxynitrile.

    Model answer

    Potassium cyanide with dilute sulfuric acid is used, so that hydrogen cyanide is generated in the mixture together with a supply of cyanide ions.

  2. 2

    Name the product formed when ethanal reacts with hydrogen cyanide.

    Model answer

    The product is 2-hydroxypropanenitrile.

  3. 3

    Name the product formed when propanone reacts with hydrogen cyanide.

    Model answer

    The product is 2-hydroxy-2-methylpropanenitrile.

  4. 4

    Explain why the hydroxynitrile obtained from ethanal is optically inactive.

    Model answer

    The carbonyl group is flat, so the cyanide ion is equally likely to attack either face, and the two enantiomers are produced in equal amounts as a racemic mixture whose rotations cancel.

  5. 5

    Explain why the hydroxynitrile obtained from propanone has no chiral centre.

    Model answer

    The central carbon carries two identical methyl groups, so it does not have four different groups attached.

  6. 6

    Explain why a trace of alkali or of a cyanide salt is needed rather than hydrogen cyanide alone.

    Model answer

    Hydrogen cyanide is a weak acid and dissociates very little, so on its own it provides too few of the cyanide ions that act as the attacking nucleophile.

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