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22.8 Reactions of Anhydrides

  • Page ID
    28419
  • This page explains what acid anhydrides are and looks at their simple physical properties such as boiling points. It introduces their chemical reactivity in a general way. A carboxylic acid such as ethanoic acid has the structure:

    ethacid.gif

    If you took two ethanoic acid molecules and removed a molecule of water between them you would get the acid anhydride, ethanoic anhydride (old name: acetic anhydride).

    ethanhydride.gif

    You can actually make ethanoic anhydride by dehydrating ethanoic acid, but it is normally made in a more efficient, round-about way

    Acid Anhydrides react with water to form carboxylic acids

    General Reaction

    File:/C:\Users\Gantor\AppData\Local\Temp\msohtmlclip1\01\clip_image002.png

    Example 1:
    2.jpg

    Mechanism

    1) Nucleophilic Attack by the water molcule

    File:/C:\Users\Gantor\AppData\Local\Temp\msohtmlclip1\01\clip_image006.png

    2) Deprotonation by pyridine

    File:/C:\Users\Gantor\AppData\Local\Temp\msohtmlclip1\01\clip_image008.png

    3) Leaving group removal

    File:/C:\Users\Gantor\AppData\Local\Temp\msohtmlclip1\01\clip_image010.png

    4) Protonation of the carboxylate

    File:/C:\Users\Gantor\AppData\Local\Temp\msohtmlclip1\01\clip_image012.png

    Acid Anhydrides react with alcohols to form esters

    Reactions of anhydrides use Pyridine as a solvent

    1a.jpg

    2a.jpg

    Example 1:
    3a.jpg

    Mechanism

    1) Nucleophilic Attack by the Alcohol

    4a.jpg

    2) Deprotonation by pyridine

    5a.jpg

    3) Leaving group removal

    6a.jpg

    4) Protonation of the carboxylate

    7a.jpg

    Acid Anhydrides react with amines to form amides

    General Reaction

    1.jpg

    Example 1:
    2.jpg

    Mechanism

    1) Nucleophilic Attack by the Amine

    3.jpg

    2) Deprotonation by the amine

    4.jpg

    3) Leaving group removal

    5.jpg

    Contributors

    Prof. Steven Farmer (Sonoma State University)

    • Layne A. Morsch - University of Illinois Springfield
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