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Amides Reactions

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

In this lesson we will get a brief overview of amides and survey some of the more important reactions involving this very important organic functional group.

How Important Are Amides?

Did you know that without the amide functional group, life would not be possible? That's right, we need amides to live. You see, proteins are made up of amino acid building blocks, and actually an amide bond is what links different amino acids together to make the different proteins in all living systems! Let's now take a few minutes to explore how amides behave in terms of their electronic nature and the reactions they undergo!

Electronic Structure

One of the most interesting aspects of amides is that unlike other carbonyl-containing compounds (meaning compounds containing a carbon-oxygen double bond), they don't usually undergo addition of nucleophiles to the carbonyl carbon. Why might this be the case? The answer lies in the resonance structure that we can draw for any amide. Because we can delocalize the lone pair on nitrogen, this destroys most of the electrophilic nature of the carbonyl, which ultimately explains why it doesn't react with nucleophiles.

Resonance contributors of an amide
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In addition to amides being non-electrophilic, the nitrogen atom isn't all that basic at all, with again the delocalization of the lone pair on nitrogen being the contributing factor.

Classification of Amides

Amides are commonly classified based on the number of hydrogen atoms the nitrogen has attached to it. A primary amide has two hydrogens bonded to nitrogen, a secondary has one, and a tertiary amide has none.

Amide classification based on hydrogen substitution
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Reactions of Amides

How to Make an Amide

One of the most common methods to make an amide is to take a carboxylic acid and convert it to an acid chloride by using thionyl chloride (SOCl2). An acid chloride is a very reactive building block and just exposing them to aqueous ammonia solution will trigger formation of our amide!

Making
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If we want to make a secondary or a tertiary amide, we only need to adjust our reaction to incorporate various organic amines in the place of ammonia to provide these substitution products.

Preparation of secondary and tertiary amides
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Acid-Promoted Hydrolysis of Amides

Amides can undergo hydrolysis in the presence of aqueous acid, however the reaction is usually VERY sluggish and requires high temperatures in order to proceed. The products are always a carboxylic acid and an ammonium salt.

Amide hydrolysis under acidic conditions
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Base-Promoted Hydrolysis of Amides

Amides can also be hydrolyzed under basic conditions, such as with sodium hydroxide, to give carboxylate salts and ammonia. This is just like in the acid case, often forcing conditions are required such as high temperatures.

Amide hydrolysis under basic conditions
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Reduction of an Amide

Amides can be reduced to amines, but a very strong reducing agent like lithium aluminum hydride is needed. In this reaction, the carbon-oxygen bond is broken and replaced with two carbon-hydrogen bonds to give an amine product.

Reduction of an amide with lithium aluminum hydride to provide an amine
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Amides as a Gateway to Nitriles

If we take an amide and react it with thionyl chloride (SOCl2), the organic product is a nitrile (carbon-nitrogen triple bond). We also get sulfur dioxide gas and HCl gas as by-products and for this reason, this reaction must always be carried out in a fume hood to limit exposure to these toxic substances.

Nitrile synthesis from and amide
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