Amide - an organic compound that contains a carbonyl group (-CO-) bonded to a nitrogen atom.
Amides are structurally similar to esters, except the two chains are joined by a nitrogen atom next to a carbonyl group rather than by an oxygen atom.
Carboxylic acids react with ammonia, primary amines, and secondary amines to produce amides.
A covalent bond between two consecutive amino acids along a peptide or protein chain forms an amide bond, also known as a peptide bond.
The name of an amide has three parts:
- the first part from the amine;
- the second part from the acid; and
- the ending, which is always the suffix -amide.
For example, the reaction of methanamine and butanoic acid will produce an amide: N-methylbutanamide.
Physical properties of amides
The smaller amides are somewhat soluble in water. This can be explained by the molecules’ structure: the –NH groups form hydrogen bonds with water molecules.
As the length of the carbon chain increases, solubility decreases.
Amides are (mainly) solids at room temperature and have very high boiling points.
Methanamide and its N-methyl and N,N-dimethyl derivatives (the simplest 1°, 2°, and 3° amides, respectively), are all liquids at room temperature. All unbranched primary amides, except methanamide, are solids at room temperature, as are most other amides.
Biologically Active Amides
The simplest naturally occurring amide is urea (also known as carbamide) with the chemical formula CO(NH2)2. It is a water-soluble white solid compound produced in the human body by the liver from carbon dioxide and ammonia and excreted by the kidney as a component of urine.
Paracetamol is an amide (among other things). Acetaminophen (N-acetyl-para-aminophenol (APAP), also known as Paracetamol) is a pain reliever (analgesic) and a fever reducer (antipyretic). It is typically used for mild to moderate pain.
Aspartame (APM, Methyl L-α-aspartyl-L-phenylalaninate) is a low-calorie artificial sweetener used as a sugar substitute in a number of foods. It is methyl ester of the dipeptide, which consist of two natural amino acids - aspartic acid and phenylalanine.
Neotame is an artificial sweetener that is from 7,000 to 13,000 times sweeter than sucrose (table sugar). It is chemically similar to the aspartame.
Barbiturates, which are cyclic amide compounds, are a group of drugs that cause relaxation (tranquilizers), sleep (sedatives), and death (overdoses).
All barbiturates are derivatives of barbituric acid, a cyclic amide that was first synthesized from urea and malonic acid.
Melatonine (N-acetyl-5-methoxy tryptamine) is a polyfunctional amide: amine and ether groups are also presents. It is a natural hormone that is produced in the body by the pineal gland.
Formation and hydrolysis of amides
Amides can be synthesized by the condensation reaction of a carboxylic acid with ammonia or primary or secondary amines.
Amides do not behave like bases.
Although the amide bond is difficult to break, hydrolysis of an amide is possible with heating in the presence of either a strong acid or a strong base.
Acidic or basic hydrolysis conditions have an effect on the products.
- Acidic conditions convert the product amine to an amine salt.
- Basic conditions convert the product carboxylic acid to a carbolic acid salt.