Amides
Amides
An amide is a nitrogen-containing compound that can be considered a derivative of ammonia, NH3. Organic amides contain the group (–C=O). The simplest organic amide is methamide,
Inorganic amides consist of a metal or some other cation combined with the amide ion (–NH2), as in sodium amide (NaNH2). Inorganic amides are less important than their better-known organic cousins, although one member of the inorganic family, sodium amide, has applications as a dehydrating agent and in the production of the dye indigo, the rocket fuel hydrazine, sodium cyanide, and other compounds.
Classification and properties
Like amines, the amides can be classified as primary, secondary, or tertiary, depending on the number of hydrogen atoms substituted in the ammonia molecule. An amide containing the –NH2 group is a primary amide; one containing the –NH group is a secondary amine; and one containing the –N– group is a tertiary amine.
Although amides and amines both contain an amino group (–NH2, NH or N), the former are much weaker bases and much stronger acids than the latter. Amides undergo many of the same reactions as other derivatives of organic acids. For example, they undergo hydrolysis to produce the parent carboxylic acid and ammonia. They can also be dehydrated with a strong agent such as diphosphorus pentoxide, P2 O5. The product of this reaction, a nitrile, a compound containing the –C=N group, is widely used in the synthesis of other organic compounds.
Some familiar amides
Proteins can be considered the most common examples of amides in the natural world, and synthesizing a protein forms an amide bond between adjacent amino acids. A naturally occurring amide is nicotinamide, one of the B vitamins. A third familiar natural amide is urea, also known as carbamide. Urea is the compound by which otherwise toxic wastes are excreted from mammalian bodies.
Important synthetic amides
Perhaps the best known of all synthetic amides is the fiber known as nylon. In 1931, the American chemist Wallace Hume Carothers discovered a process for making one of the first synthetic fibers. He found that adding adipic acid to hexamethylene dia-mine produced a strong, fiber-like product to which he gave the name Nylon 66. (The 66 reflects the fact that adipic acid and hexamethylene diamine each contain six carbon atoms in their molecules.)
The reaction between these two substances forms a long polymer, somewhat similar to the structure of natural protein. As in protein, nylon’s subunits are joined by amide bonds. For this reason, both protein and nylon can be thought of as polyamides—compounds in which a large number of amide units are joined to each other in a long chain.
Other types of nylon were developed at later dates. One form, known as Nylon 6, is produced by polymerizing a single kind of molecule, 6-aminohexanoic acid. The bonding between subunits in Nylon-6-amide bonds is the same as it is in Nylon 66. In all types of nylon, the fiber gets its strength from hydrogen bonding that occurs between oxygen and hydrogen atoms on adjacent chains of the material.
Another type of polymer is formed when two of the simplest organic compounds, urea and formaldehyde, react with each other. In this reaction, amide bonds form between alternate urea and formaldehyde molecules, resulting in a very long polyamide chain. Urea formaldehyde polymers are used as molding compounds, in the treatment of paper and textiles, and as a binder in particle board, to mention but a few uses.
KEY TERMS
Amide ion— An anion with the formula –NH2.
Hydrogen bond— A weak chemical bond that results from the electrical attraction between oppositely charged particles, usually a hydrogen ion and an oxygen-containing ion.
Nylon— A group of synthetic fibers; large polymers held together by amide bonding.
Polymer— A large molecule made up of many small subunits repeated over and over again.
Protein— Any large naturally occurring polymer made of many amino acids bonded to each other by means of amide bonds.
An amide with which many people are familiar is acetaminophen, an analgesic (painkiller) that is the active ingredient in products such as Amadil, Cetadol, Datril, Naprinol, Panadol, and Tylenol. Another amide analgesic is phenacetin, found in products such as APC (aspirin, phenacetin, and caffeine) tablets and Empirin.
Other commercially important amides include the insect repellant N, N-dimethyl-m-toluamide (Off, DEET), the local anesthetics lidocaine (Xylocaine) and dibucaine (Nupercaine), the tranquilizer meprobromate (Miltown, Equaine), and the insecticides Sevin and Mipcin.
See also Artificial fibers.
Resources
BOOKS
Carey, Francis A., and Richard J. Sundberg Advanced Organic Chemistry: Structure and Mechanisms. 4th ed. New York: Plenum, 2001.
Carey, Francis A. Organic Chemistry. New York: McGraw-Hill, 2002.
Joesten, Melvin D., David O. Johnston, John T. Netterville, and James L. Wood. World of Chemistry. Belmont, CA: Brooks/Cole Publishing Company, 1995.
Ouellette, Robert. Chemistry: An Introduction to General, Organic, and Biological Chemistry. Prentice Hall, 1994.
OTHER
“Understanding Chemistry: Amides Menu” Chemguide: Helping You to Understand Chemistry <http://www.chemguide.co.uk/organicprops/amidemenu.html> (accessed October 14, 2006).
David E. Newton