On the basis of how the hydrogen atoms are replaced by an ammonia molecule, amines can be divided into 4 types.
- Primary AminesWhen one of the hydrogen atoms of the ammonia molecule is replaced by an alkyl or aryl group.Eg: Methylamine CH3NH2, Aniline C6H5NH2
- Secondary AminesTwo organic substituents replace the hydrogen atoms of the ammonia molecule forming an amine.Eg: Dimethylamine (CH3)2NH, Diphenylamine (C6H5)2NH
- Tertiary AminesWhen all 3 of the hydrogen atoms are replaced by an organic substituent, it could be an aryl or aromatic group.Eg: Trimethylamine N(CH3)3, Ethylenediaminetetraacetic acid (EDTA)
- Cyclic AminesThese are secondary or tertiary amines in an aromatic ring structure. Eg: Piperidine (CH2)5NH, Aziridines C2H5N
Preparation of Amines
Some processes for preparing primary amines are mentioned below.
Preparation of Primary Amines
1. Making of amines from halogenoalkanes
This process will be carried out in a sealed tube. Here haloalkanes will be heated with the concentrated solution of ammonia in ethanol. The mixture cannot be heated under the reflux as ammonia would move out in the form of gas from a container.
Now coming to the preparation of primary amine from halogenoalkane, the reaction takes place in two stages. Salt will be formed at the first stage. Here ethyl ammonium bromide is the salt. It is similar to ammonium bromide except for the fact that one of the hydrogens in the ammonium atom is replaced by an ethyl group.
A reverse reaction can occur between ammonia and the salt. It is illustrated in the above reaction.
2. Reduction of nitriles
We can get primary amines when nitriles are reduced with lithium aluminium hydride. This method is mainly used for the preparation of amines which contain one carbon atom more than the starting amine.
3. Gabriel phthalimide synthesis
We can get primary amines easily by Gabriel synthesis. In this process, on the treatment of phthalimide with ethanolic potassium hydroxide, we get potassium salts of phthalimide. When this is further heated with alkyl halide followed by alkaline hydrolysis then primary amine is produced. We cannot prepare aromatic primary amines because aryl halides do not undergo nucleophilic substitution with the anion which is formed by phthalimide.
Basicity of Amines
Similar to ammonia, primary & secondary amines have protic hydrogens and thus they showcase a degree of acidity. Whereas tertiary amines have no protic hydrogen and thus do not possess a degree of acidity.
pKa value for primary & secondary amines is about 38, which makes them a real weak acid. Whereas if we take the pKb, it is about 4. This makes the amines much more basic than acidic. Thus, an aqueous solution of an amine is strongly alkaline.
Uses of Amines
Amines have a widespread application in our daily lives. Some uses of amines are listed below:
- It is used in water purification, medicine manufacturing and development of insecticides and pesticides.
- It is involved in the production of amino acids which is the building block of proteins in living beings. Many varieties of vitamins are also made by amines.
- Serotonin is an important amine that functions as one of the primary neurotransmitters. It controls the feelings of hunger and is critical for the speed with which the brain operates in general.
- Pain-relieving medicines such as Morphine and Demerol which are also known as analgesics are made from amines.
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