Amines

Introduction to Amines – Compounds Containing Nitrogen

Amines are one of the most important groups of organic compounds formed when one or more hydrogen atoms of an ammonia molecule are replaced with an alkyl group.

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What are Amines?

In general, an amine is a functional group containing a nitrogen atom with a lone pair. Structurally, amines resemble ammonia because nitrogen may form bonds with up to three hydrogen atoms. Additionally, it possesses varied properties based on carbon connection.

Compounds containing nitrogen bonded to a carbonyl group are known as amides; their structure is R–CO–NR′R′′ and their characteristics differ from those of amines.

Amines are chemical molecules that contain lone pairs of nitrogen atoms. In essence, they are generated from ammonia (NH3) in which one or more hydrogen atoms are substituted by an alkyl or aryl group, hence their respective names of alkylamines and arylamines.

Amine Structure

Nitrogen has five valence electrons and is hence a trivalent element with a lone pair. According to the VSEPR theory, the nitrogen in amines is sp3 hybridized and, due to the existence of a lone pair, has a pyramidal structure rather than the tetrahedral form typical of most sp3 hybridized molecules. Depending on the configuration of amines, each of the three sp3 hybridized orbitals of nitrogen overlap with orbitals of hydrogen or carbon. The C-N-H angle in amines is less than 109 degrees, which is a hallmark angle of tetrahedral geometry, due to the existence of a lone pair. The amines’ angle is around 107 degrees.

Occurrence of Amines

Amines occur naturally in proteins, vitamins, hormones, etc., and they are also synthesized to produce polymers, medicines, and pigments.

Types of Amines

On the basis of the manner in which hydrogen atoms are replaced by an ammonia molecule, amines can be categorized into four distinct categories.

Primary Amines

When an alkyl or aryl group is substituted for one of the hydrogen atoms in the ammonia molecule.

Example: Methylamine (CH3NH2) and Aniline (C6H5NH2)

Secondary Amines

Two organic substituents replace the ammonia molecule’s hydrogen atoms to make an amine.

Dimethylamine (CH3)2NH and Diphenylamine (C6H5)2NH are examples.

Tertiary Amines

When all three hydrogen atoms are replaced with an organic substituent, the resulting group may be aryl or aromatic.

Trimethylamine N(CH3)3, Ethylenediaminetetraacetic acid are examples of compounds (EDTA)

Cyclic Amines

These amines have an aromatic ring structure and are secondary or tertiary.

Eg: Piperidine (CH2)5NH, Aziridines C2H5N

Preparation of Primary Amines

1. Making of amines from halogenoalkanes

This procedure will be conducted in an airtight tube. Here, haloalkanes will be heated with a concentrated ammonia-ethanol solution. The mixture cannot be heated under reflux because ammonia would escape the container as a gas.

Regarding the preparation of primary amine from halogenoalkane, there are two steps to the reaction. In the initial stage, salt is produced. Here, the salt is ethyl ammonium bromide. It is similar to ammonium bromide except that one of the ammonium atom’s hydrogens has been replaced by an ethyl group.

The reaction between ammonia and salt is reversible. It is demonstrated by the preceding reaction.

2. Reduction of nitriles

By reducing nitriles using lithium aluminium hydride, primary amines can be produced. This procedure is mostly used to create amines with one additional carbon atom than the beginning amine.

3. Gabriel phthalimide synthesis

Through Gabriel synthesis, it is simple to acquire primary amines. In this procedure, phthalimide is treated with ethanolic potassium hydroxide to produce phthalimide potassium salts. This produces primary amine upon additional heating with alkyl halide followed by alkaline hydrolysis. Because aryl halides do not undergo nucleophilic substitution with the anion generated by phthalimide, it is not possible to prepare aromatic primary amines.

Basicity of Amines

Similar to ammonia, primary and secondary amines contain protic hydrogens and, as a result, exhibit some acidity. Tertiary amines, on the other hand, lack protic hydrogen and so lack acidity.

The pKa value of primary and secondary amines is approximately 38, making them extremely weak acids. In contrast, the pKb value is around 4. This renders amines far more basic than acidic. Thus, an amine’s aqueous solution is highly alkaline.

Uses of Amines

Amines have numerous applications in everyday life. Listed below are some uses for amines:

• It is utilized in water purification, drug production, and the creation of insecticides and herbicides.
• It contributes to the synthesis of amino acids, the building blocks of proteins in living organisms. Several types of vitamins are also produced by amines.
• Serotonin is an essential amine that serves as one of the principal neurotransmitters. It governs the sensations of hunger and is essential for the normal operation of the brain.
• Analgesic medications such as Morphine and Demerol, generally known as analgesics, are derived from amines.

Students should now have a basic understanding of the fundamental ideas of amines, but if they want to learn more about the chemical and physical features of amines, Visit Utopper.com

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