Notes on Amines

Groups of nitrogen atoms, each possessing a single pair of electrons. An amine is a structural analogue of ammonia, in which nitrogen can bind up to three hydrogen atoms with the help of hydrogen bonds. It also has a variety of features that stem from its carbon-based structure.

Amines constitute a significant class of organic compounds. Amines are organic compounds that consist of nitrogen atoms with a single pair. 

Amines are derivatives of ammonia. The general formula for amines is R3-xNHx , where R is a group and 0 < x < 3. 

Types of Amines

Amines can be categorised into four distinct types. These are:

Primary Amines 

This amine type appears when one of the three hydrogen atoms is replaced with an alkyl or aromatic group. 

For example: Methyl Amine, CH3NH2

Secondary Amines

This type of amine occurs when the amino group is precisely bonded to two carbons of any hybridisation. However, the carbons cannot be carbonyl group carbons. 

For example: Dimethyl Amine

Tertiary Amines

A tertiary amine comprises molecules that consist of three C-N bonds and no H-N bonds. For example: Trimethylamine

Nomenclature of Amines

Because of a wide variety of amines, specific rules must be followed in naming them to avoid confusion while communicating about these substances. Some of these rules are as follows:

We name aliphatic amines with the standard naming system by prefixing an alkyl group to an amine, alkylamine. For example: n-propylamine and isobutyl amine.

Secondary amines and tertiary amines that retain two or more equal groups are named by adding the prefix ‘di’ or ‘tri’ before the name of the alkyl group. For example: trimethylamine and dimethylamine. 

Aromatic amines are named as derivatives of the parent group, aniline. For example: o-Toluidine and p-Bromoaniline.

Structure of Amines

Nitrogen is trivalent with a lone pair because it possesses five valence electrons. Nitrogen in amines is sp3 hybridised according to VSEPR theory. Because of the existence of a lone pair, it has a pyramidal shape rather than a tetrahedral shape common to most sp3 hybridised compounds. Depending on the structure of amine, each of nitrogen’s s three sp3 hybridised orbitals overlaps an orbital of hydrogen or carbon. Amines’ C-N-H angle is less than 109 degrees, which is a typical angle of tetrahedral geometry, as a lone pair is present. Amines have a rotational axis of 107°.

Alkyl Amines

The nitrogen centres in alkylamines are tetrahedral. The C-N-C and C-N-H bond angle is 109° in this instance. The C-N distance is smaller than the C-C distance. The nitrogen centre of the amines can also hold four replacements to produce lone pairs, giving them chirality.

Aromatic Amines

In aromatic amines (anilines), nitrogen virtually possesses a planar structure. It is because the aryl substituent is mixed in with the lone pair. The C-N frequency range is narrower. As with C-C and C-C for aniline, C-N is the same as C-C for aniline.

Preparing Amines

Amines can be prepared in many ways. Some of these include:

The reduction of nitro compounds

Nitro compounds are reduced to amines by introducing hydrogen gas in finely distributed nickel, palladium, or platinum and lowering the metals in an acidic medium. In response to alkanamines, the nitroalkanes can be similarly reduced. Thus, only a small quantity of hydrochloric acid is needed to begin the reaction.

The ammonolysis of alkyl halides

An alkyl and benzyl halides on reaction with an ethanolic solution of ammonia undergoes a nucleophilic substitution reaction in which the halogen atom is renovated by an amino (–NH2) group. Consequently, this splitting of the C–X bond by an ammonia molecule is known as ammonolysis.

The reduction of nitriles

When lithium aluminium hydride decreases nitriles, we can obtain primary amines. This technique is most commonly used for amines with one more carbon atom than the beginning amine.

On removal with lithium aluminium hydride (LiAlH4) or catalytic hydrogenation, the nitriles generate primary amines. 

The reduction of amides

This amide on the contraction with lithium aluminium hydride results in amines.

The Gabriel Phthalimide Synthesis

The Gabriel Phthalimide Synthesis is used in the preparation of primary amines. However, this process cannot create primary aromatic amines because aryl halides cannot undergo nucleophilic substitution with the anion established by phthalimide.

The Hoffmann Bromamide Degradation Reaction

Hoffmann formulated a technique for preparing primary amines by adding an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide.

The Uses of Amines

Amines have many uses in the 21st century. 

They are, for example, widely used in the pharmaceutical industry and the manufacture of personal care products. They are especially effective for purposes of disinfection and tanning. 

Amines are also widely used to produce azo-dyes and nylon fibre in the fashion industry.

Amines are also crucial to farming industries as they are widely used in pesticides and other substances critical to preserving crops. Amines are also widely used for water purification.

Amines are vital within the body too. Hormones such as serotonin, a neurotransmitter, are made up of amines. Serotonin controls feelings such as hunger and happiness. 

Amines are also found in novocaine, an anaesthetic. 

CatecholAmine

Catecholamines are hormones produced by nerve tissues, the brain, and adrenal glands. Our body discharges catecholamines in reaction to personal or physical anxiety. These are hormones that function as neurotransmitters.

There are several types of catecholamines, including:

Dopamine

Dopamine is a neurotransmitter that heavily influences movement, emotions, memory, and the brain’s reward mechanism. 

Adrenaline

Adrenaline, also known as epinephrine, is the neurotransmitter responsible for the fight-or-flight reaction of a living organism. When a person is stressed, our body releases adrenaline to improve blood flow to the muscles, lungs, and heart. It is an important survival mechanism.

Noradrenaline

Noradrenaline, also known as norepinephrine, is the neurotransmitters responsible for increasing a living being’s heart rate and blood flow. Noradrenaline is also involved in concentration levels and mood regulations. 

Conclusion

Amines are essential to the survival of many animals, including human beings. Amines are central to the composition of amino acids, the building blocks of proteins in living things. Several vitamins are similarly created from amino acids. Amines are essential compounds because of the lone set of electrons. The Gabriel synthesis is utilised for the preparation of primary amines.