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3.9: Chemistry of Amides- Synthesis and Reactions

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    227548
  • Synthesis of Amides

     

    Direct reaction of a carboxylic acid with an amine does not produce an amide, but a salt.

    Ammonium salt.png

    Therefore, we need to use acyl chlorides or anhydrides as an alternative.

    Acid chlorides react with ammonia, 1o amines and 2o amines to form amides

    Amide formation 1.png

     

    Acid Anhydrides react with ammonia, 1o amines and 2o amines to form amides

    Amide formation 2.png

    Examples

    Examples amide formation .png

    Tertiary amines cannot form amides due to the lack of H atom that can be replaced by the acyl group

    Chemical properties of Amides

    Hydrolysis under acidic conditions

    Taking acetamide (ethanamide) as a typical amide. If acetamide is heated with a dilute acid (such as dilute hydrochloric acid), acetic acid is formed together with ammonium ions. So, if you were using hydrochloric acid, the final solution would contain ammonium chloride and acetic acid.

    acid hydrolysis.png

    Hydrolysis under alkaline conditions

    Also, if acetamide is heated with sodium hydroxide solution, ammonia gas is given off and you are left with a solution containing sodium acetate.

    basic hydrolysis.png

    Peptide hydrolysis

    Peptide hydrolysis of proteins is amide hydrolysis. What biologists and biochemists call a peptide link (in proteins, for example) is what chemists call an amide link. Apply either hydrolysis reaction above to the dipeptide below to produce two amino acids. The amines in the products are shown in their protonated form because this hydrolysis reaction was performed under acidic conditions.

    hydrolprotein.gif

     

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