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Structure and properties of amines

The nitrogen atom in an amine has a lone pair


of electrons and it can be considered as a base, like ammonia. Amines with less than five carbon atoms can be mixed with water. Water solutions of amines are basic. Almost all such solutions can be dissolved in dilute acid. Since acids and bases combine to form salts, such a solution of amines in dilute acid forms soluble ammonium salts.

Primary and secondary amines do not form hydrogen bonds as strongly as do alcohols. Thus, their boiling points lie between those of the corresponding hydrocarbons and alco­hols. Tertiary amines have boiling points slightly higher than the corresponding hydro­carbon. Thus, the methylamines are all gases at room temperature. Simple amines have a distinct odor of rotting fish, whose characteris­tic smell is caused by amines produced by bacteria.

Preparation and reactions: amines and amides

Formation of primary amines is most impor­tant because secondary and tertiary com­pounds can be made from them. There are various synthetic methods of producing pri­mary amines. These include the treatment of certain compounds with ammonia or the re­duction of nitrogen-oxygen compounds. In general, one or more of the three hydrogen atoms of ammonia is replaced with an organic group containing carbon and hydrogen.

Primary amines can be converted to sec­ondary amines. They can also be converted to secondary amides. An amide is an ammonia or amine derivative in which the nitrogen atom is attached to the organic group. Primary amines are also convertible to imines (organic com­pounds with a carbon-nitrogen double bond). Imines are very reactive. Secondary amines react similarly, but less vigorously. In tertiary amines, each of the hydrogen atoms is re­placed by an alkyl group, an organic corn-



Amines,and proteins de­rived from them, occur in the tissues of all animals. In dead fish, particularly, amines reveal their pres­ence through their charac­teristic "fishy" smell.


Organic chemistry: Nitrogen compounds 89


Aromatic nitrogen compounds NH

Indole

Pyrrole

pound consisting solely of carbon and hydro­gen atoms.


Date: 2015-12-11; view: 159


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