Amines: Nomenclature

In organic chemistry, amines are compounds and functional groups that include a basic nitrogen atom with a lone pair, as opposed to other compounds and functional groups. Amines are formal derivatives of ammonia, in which one or more hydrogen atoms have been replaced by a substituent, such as an alkyl or aryl group, to generate a more stable compound (these may respectively be called alkylamines and arylamines; amines in which both types of the substituent are attached to one nitrogen atom may be called alkyl aryl amines). Naturally occurring amines include the alkaloids, which are present in certain plants; the catecholamine neurotransmitters (i.e., dopamine, adrenaline, and norepinephrine); and a local chemical mediator, histamine, that occurs in most animal tissues.

Aniline, ethanolamines, and various other amines are important industrial commodities that are used in the production of rubber, dyes, medicines, synthetic resins and fibers, as well as a variety of other products and processes. Most of the numerous methods for the preparation of amines may be broadly divided into two groups: (1) chemical reduction (replacement of oxygen with hydrogen atoms in the molecule) of members of several other classes of organic nitrogen compounds and (2) reactions of ammonia or amines with organic compounds.

Amines are divided into three categories: primary, secondary, and tertiary. The classification is based on whether one, two, or three hydrogen atoms in ammonia have been replaced by organic groups. In chemical notation, these three classes are written as RNH₂, R₂NH, and R₃N, respectively. The fourth category of ammonium compounds is formed by replacing all four hydrogen atoms of the ammonium ion, NH⁴⁺, with nitrogen atoms; an anion (R₄N+X) must be present in order for the compound to be formed. Amines can also be classed as aliphatic, meaning that they solely include aliphatic groups, or aromatic, meaning that they contain one or more aryl groups. A cyclic nitrogen molecule can be either open-chain, in which the nitrogen does not form part of any rings, or closed-chain, in which the nitrogen does form part of any rings (generally aliphatic).

Nomenclature of Amines

Amines are derivatives of ammonia in which one or more of the hydrogens has been replaced by an alkyl or aryl group. The nomenclature of amines is complicated by the fact that numerous alternative nomenclature schemes exist, and there is no apparent preference for one over the others. The designations primary (1º), secondary (2º), and tertiary (3º) are also used to describe amines in an entirely different way than they are used to define alcohols or alkyl halides, which is a relevant difference. When applied to amines these phrases relate to the number of alkyl (or aryl) substituents linked to the nitrogen atom, meanwhile, in other circumstances, they refer to the type of an alkyl group.

• IUPAC names:

An amino group is a name given to the simple -NH substituent found in 1º-amines. The names of all alkyl groups except the root alkyl group are included in the compound prefix (e.g dimethylamino in the fourth example) for 2º and 3º-amines.

• The Chemical Abstract Service has developed a nomenclature method in which the suffix -amine is appended to the root alkyl name. This is equivalent to the IUPAC alcohol nomenclature in the case of 1º-amines such as butanamine (as a first example) (-ol suffix). The additional nitrogen substituents in 2º and 3º-amines are denoted by the prefix N- well before the group name, which stands for nitrogen-containing.

• For simplicity’s sake, we’ll use the suffix -amine to refer to each alkyl substituent on nitrogen in alphabetical sequence, followed by the suffix amine.

Classification of Amines

Amines are divided into four types, which are as follows: primary, secondary, tertiary, and cyclic amines. In the presence of an alkyl or aryl group, one of the three hydrogen atoms is changed, resulting in the formation of a primary amine. It is possible to produce secondary amines by replacing two out of three hydrogen atoms; however, it is only possible to produce third-generation amines when all three hydrogen atoms are changed. Cyclic amines are only found in secondary or tertiary amines; aziridine, which has a three-membered ring, is an example of a cyclic amine.

Physical Properties of Amines

• Lower aliphatic amines occur naturally as gaseous compounds with a distinct fishy odour. Primarily amines containing three or four carbon atoms are liquids at room temperature, whereas higher-order amines are solids at this temperature.

• Aniline and other arylamines are normally colourless, but they can become coloured if left out in the open for an extended period of time due to atmospheric oxidation.

• Lower aliphatic amines have the ability to make hydrogen bonds with water molecules, which is why they are water-soluble. The molar mass of amines increases as the size of the hydrophobic alkyl portion increases, which leads to a decrease in the solubility of the amine in water. Higher amines are insoluble in water at all concentrations.

• Organic solvents such as alcohol, benzene, and either have a high affinity for amine dissolution. Alcohols have higher polarity than amines, and as a result, they generate stronger intermolecular hydrogen bonds than amines do.

• Primary and secondary amines are frequently involved in the intermolecular association as a result of hydrogen bonding between the nitrogen of one molecule and the hydrogen of the other molecule, which occurs as a result of nitrogen bonding between the two molecules.

• When comparing primary and secondary amines, the intermolecular interaction is more apparent in the former than in the latter due to the presence of two hydrogen atoms.

• Because there is no free hydrogen atom for bonding in tertiary amines, there is no intermolecular interaction in these compounds. The boiling points of amines are listed in the following order: Primary is followed by secondary and finally tertiary.

Basic Character of Amines

Amines are basic in nature due to the existence of a lone pair of electrons on nitrogen, which causes them to be electronegative.

In order to compare the basicities of amines and ammonia, it is necessary to look at the availability of a pair of electrons on the nitrogen atom. When dissolved in water, ammonia and amines both attract a proton from the water, resulting in the formation of ammonium or alkylammonium ions, respectively, and a hydroxide ion.

As we progress from primary to secondary to tertiary amines, the basicities of the amines would become more pronounced.

However, it has been discovered that the following is the correct sequence of the fundamentals:

Primary < Tertiary > Secondary

The tertiary amines have lower basicity than the secondary amines, making them less reactive. The explanation for this is that a tertiary amine, despite the fact that it has three alkyl groups that can give electrons to the nitrogen atom, does not do so.

In addition, they induce crowding (steric hindrance) around the nitrogen atoms. As a result, the protonation of the nitrogen atom is hindered, and the basicity of the compound is reduced.

A characteristic of aromatic amines that distinguishes them from ammonia is that the aromatic ring is electron-withdrawing. It decreases the electron density at nitrogen and makes the aromatic amines less basic.

Aromatic amines < Ammonia < Aliphatic amines

Conclusion

Among the most essential roles that amino acids play in the survival of life – their involvement in the production of amino acids, which are the building blocks of proteins in living organisms. A large number of vitamins are also derived from amino acids. Serotonin is an important amine that serves as one of the brain’s key neurotransmitters, acting as a mood stabiliser.

Amines are basic compounds due to the presence of a lone pair of electrons in their atoms. The basicity of the molecule can be impacted by surrounding atoms, steric bulk, and the solubility of the matching cation to be generated. Amine compounds can hydrogen bond, which provides them solubility in water and increased boiling temperatures. In daily life activities amines are used for insect control and tanning of leather. They find considerable applications in man-made dyes. Amines are utilised in creating azo-dyes and nylon separate from medicines and drugs. Their products are frequently employed in the development of chemicals for crop protection, medication, and water purification, among other things.