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15.16 Formation of Amides

Learning Objective

  1. Describe the preparation procedure for amides.

The addition of ammonia (NH3) to a carboxylic acid forms an amide, but the reaction is very slow in the laboratory at room temperature. Water molecules are split out, and a bond is formed between the nitrogen atom and the carbonyl carbon atom.

In living cells, amide formation is catalyzed by enzymes. Proteins are polyamides; they are formed by joining amino acids into long chains. In proteins, the amide functional group is called a peptide bond. (For more information about proteins, see Chapter 18 "Amino Acids, Proteins, and Enzymes", Section 18.4 "Proteins".)

Polyamides

Just as the reaction of a diol and a diacid forms a polyester (Section 15.8 "Preparation of Esters"), the reaction of a diacid and a diamine yields a polyamideA condensation polymer in which the monomer units are joined by an amide linkage.. The two difunctional monomers often employed are adipic acid and 1,6-hexanediamine. The monomers condense by splitting out water to form a new product, which is still difunctional and thus can react further to yield a polyamide polymer.

Some polyamides are known as nylons. Nylons are among the most widely used synthetic fibers—for example, they are used in ropes, sails, carpets, clothing, tires, brushes, and parachutes. They also can be molded into blocks for use in electrical equipment, gears, bearings, and valves.

Concept Review Exercises

  1. Write the condensed structural formulas and give names of the two compounds from which butanamide (CH3CH2CH2CONH2) is formed.

  2. Write the condensed structural formulas and names of the two compounds from which CH3CH2CH2CH2CH2CONHCH2CH2CH3 is formed.

Answers

  1. CH3CH2CH2COOH (butanoic acid) and NH3 (ammonia)

  2. CH3CH2CH2CH2CH2COOH (hexanoic acid) and CH3CH2CH2NH2 (propylamine)

Key Takeaway

  • Amides are prepared by the reaction of a carboxylic acid with ammonia or an amine.

Exercises

  1. Write the condensed structural formulas and names of the two compounds from which pentanamide (CH3CH2CH2CH2CONH2) is formed.

  2. Write the condensed structural formulas and names of the two compounds from which CH3CONHCH3 is formed.

Answer

  1. CH3CH2CH2CH2COOH (pentanoic acid) and NH3 (ammonia)