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Amines - Organic Chemistry Tutor

Amines are considered ammonia derivatives resulted in the replacing process of the hydrogen atoms with hydrocarbonate's radicals. As being replaced 1, 2, 3 hydrogen atoms in the ammonia molecule, there are obtained primary amines (RHN2), secondary (R2NH) and tertiary (R3N) amines. There are also amines that contain in their molecule one or more –NH2 groups and this is why they can be mono or polyamines. Amines are named by adding the word “amine” as a suffix to the hydrocarbonate's radical. For example, CH3-NH2 is methylamine, (CH3)2-NH is dimethylamine, (CH3)3-N is trimethylamine.

Obtaining methods

1) Ammonia's action on alkyl halogens.
2) Ammonia's action on alcohols. The reaction is effectuated by passing the alcohol's vapors and ammonia mix over a catalyst (aluminum oxide) heated at 250-350C.
3) Nitro-derivatives' reduction.
4) Nitriles' reduction with active hydrogen.
5) Amides' reduction.
6) Hoffman reaction of primary amides, that consists in primary amides' reaction with brome or chlorine in the presence of alkaline hydroxides and that leads to primary amines that have a carbon atom less than the initial amide. This reaction has a special industrial significance.

Physical properties

Amines are unpleasant smell substances; the inferior amides have a smell similar to ammonia, while the superior ones smell like fish. In the aliphatic series, the inferior substances are gases, the next compounds are liquids and the superior ones are solids. In the aromatic series the inferior substances are liquids while the rest are solids. Amines' boiling temperature increases proportionally to molecular mass; primary amines boil at lower temperatures than the secondary ones while these boil at lower temperatures in comparison with the tertiary amines. For example, ethylamine boils at 16,6 degrees C, diethylamine at 55 degrees C and triethylamine at 89 degrees C. Water solubility of aliphatic amines decreases with the molecular mass' increase. In the aromatic series, amines solubility is reduced.

Chemical properties

1) The most important chemical property of amines is their basicity. As ammonia forms with water ammonium hydroxide, amines react with water in order to form quaternary ammonium bases. In the aliphatic series, secondary amines have a superior basicity in comparison with the primary or tertiary amines. In the aromatic series, basicity decreases from the primary to tertiary amines.
2) Common mineral acids react with amines in order to obtain salts that are water soluble. For example, aniline reacts with hydrochloric acid and forms phenylammonium chloride.
3) Carboxylic acids form with primary or secondary amines, at heating, acyl derivatives from amines.
4) Nitric acid reacts different depending on amines' nature. When reacting with primary aliphatic amines, nitric acid forms alcohol and liberates nitrogen. When reacting with primary aromatic amines, in acid solution, it forms a diazonium salt. When reacting with secondary aliphatic or aromatic amines, nitric acid forms nitrosamines.
5) Halogens react with primary and secondary aliphatic amines; the halogen replaces the hydrogen atom from the functional group forming halogen-amines.
6) Oxidants react with amines. Using potassium permanganate as a catalyst, primary aliphatic amines pass in aldehides while the aromatic amines pass in quinones derivatives. Secondary aliphatic and aromatic amines transform in hydrazine derivatives.

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