JEE Crash Course 2022

Amine Definition

Under organic chemistry, Amine is recognized as a derivative of ammonia. It is a chemical compound categorized under organic nitrogen compounds which contain nitrogen atoms with a lone pair of electrons. Basically, in amines hydrogen atoms are replaced by an alkyl or aryl group. With this basic animation meaning, let us study various types of amines, properties and naming systems.

 

Types of Amines

Amines are categorized based on nature into aliphatic amines and aromatic amines. Besides amines, aryl and alkyl are also divided into three subcategories which depend on the count of carbon atoms linked to nitrogen and the number of hydrogen atoms are substituted. They are as follows-

 

1) Primary Amines ( 10 Amines)

Primary amines created when an alkyl or aromatic group substitutes one of three hydrogen atoms in ammonia. Examples of primary alkyl amines include methylamine, amino acids, whereas primary aromatic amines include aniline.

 

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2) Secondary Amines (20 Amines)

Secondary amines contain two organic substituents either alkyl or aryl or both which are bound to the nitrogen together with one hydrogen. Examples include dimethylamine and aromatic Amine like diphenylamine.

 

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3) Tertiary Amine (30 Amines)

Tertiary amines are recognized where the nitrogen consists of three organic substituents. Examples of tertiary Amine are trimethylamine and EDTA.

 

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4) Quaternary Amines (40 Amines)

Quaternary amines bear a positive charge and are those where the nitrogen contains four organic substituents

 

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Interestingly, the fourth subcategory of amines known as cyclic amines also exists—cyclic amines based on the connectivity of the substituents connected to the nitrogen. However, cyclic amines are either secondary or tertiary amines. Examples are the six-membered ring piperidine or the 3-membered ring aziridine.

 

Nomenclature of Amines

The conventional and popular system for naming amines is to the recognition of each group that connected to the nitrogen atom and then suffixed it with -Amine. As in methylamine, CH3NH2; N-ethyl-N-propylamine (or ethyl(propyl)amine), CH3CH2NHCH2CH2CH3; and tributylamine, (CH3CH2CH2CH2)3N. 

 

Any or more of the listed groups are in alphabetical order; Ns or inner brackets aid to show what groups are bound to nitrogen rather than to each other.

 

Several aromatic amines and most cyclic amines have names (e.g., aniline) that might be utilized as a parent to assign the other associated, as in N, N-dimethylaniline.

 

Another method substitutes a hydrocarbon name’s terminal -e with the suffix-amine for the functional group −NH₂. The largest group preferred as the parent of secondary and tertiary amines, and the other groups were chosen as substituents.

 

Examples

1. CH3− CH2 − CH (NH2) – CH3 (2- Butylamine)

2. CH3− CH2 − CH (NHCH3) – CH3 (N – Methyl -2- Butylamine)

3. H2N − CH2– CH2– OH (Ethanolamine)

 

Properties of Amines

  • The lower aliphatic amines are gaseous with a fishy odour.

  • Primary amines are liquids at room temperature comprising three to four carbon atoms, whereas higher amines are solids.

  • Aniline and other arylamines are generally colourless. However, when stored in the open, they get painted due to atmospheric oxidation.

  • Lower aliphatic amines are soluble in water as they make the bond with the hydrogen atom of water. However, if the size of the hydrophobic alkyl portion increases, Amine molar weight decreases and solubility also decreases.

  • Lower amines in the soil are insoluble. Organic solvents such as ethanol, benzene, and ether used to dissolve amines readily.

  • Primary and secondary amines are often involved in the intermolecular interaction due to the interaction of hydrogen and nitrogen interacting with the hydrogen of other atoms.

  • Intermolecular forces are more observed in primary amines compared to secondary due to the presence of two hydrogen atoms. In contrast, tertiary amines do not have intermolecular forces due to the absence of free hydrogen atoms.

  • The more the size, the less volatile they are.

  • The odour also decreases with size, eventually becoming unnoticeable. There are some exceptions to this though. 

 

Amines are colourless. Amines with fewer than six carbons mix with water in all proportions. While aliphatic amines are bases that are stronger than ammonia, the aromatic amines are weaker than ammonia. 

 

The shape of an amine molecule is like a flattened triangular pyramid, where the nitrogen atom is at the apex. 

 

Difference between Aliphatic and Aromatic Amines

Here are some of the differences between aliphatic and aromatic amines:

  • Aliphatic amines have nitrogen directly bonding to alkyl groups and hydrogen atoms. The number of alkyl groups can go from one to three. Aromatic amines have nitrogen directly attached to at least one benzene ring. They are categorized as primary, secondary and tertiary amines, depending on how many groups are attached to the nitrogen atom. So, Alkylamines do not have benzene rings directly attached to the Nitrogen atom. In aromatic amines, at least one benzene ring is attached to the Nitrogen atom. Aliphatic amines can have aromatic rings, but with the condition that a nitrogen atom is directly attached to a carbon atom.

  • The aliphatic amines where nitrogen is one of the atoms in a ring are called heterocyclic amines. Examples of aliphatic heterocyclic amines are piperidine and pyrrolidine. There are also heterocyclic aromatic amines, but they are structurally different. Two examples of heterocyclic aromatic amines are pyrrole and pyridine.

  • While Aliphatic amines are less dense than water, aromatic amines are generally slightly heavier than water. 

  • Aliphatic amines are transparent to ultraviolet light. Aromatic amines, on the other hand, display strong absorption of certain wavelengths. 

  • Aliphatic heterocyclic amines are stronger bases as compared to aromatic heterocyclic amines.

  • Aliphatic amines are stronger bases than aromatic amines because basically, alkyl ammonium ions are more stable than aryl ammonium ions. On the other hand, all aliphatic amines are weak bases like ammonia, but they are still slightly stronger than ammonia. This is because lone pairs of electrons on a nitrogen atom are delocalized and less available for acid.

 

Fun Facts

  • Do you know about Amines generated by protein fragmentation or fermentation? Protein constituting elements, i.e. amino acids break down into amines. Amines are present in cheese, chocolates, beer, yeast extracts and fish products. They are also available in certain fruits and vegetables, e.g. bananas, avocados, tomatoes, and broad beans.

  • Do you know amines play an essential role in the survival of human beings? They are responsible for creating amino acids in living beings. Not just proteins, many vitamins are built on amino acids. Serotonin is a crucial amine that operates as neurotransmitters for the brain. It regulates the feelings of hunger, sleep regulation, and emotions; overall brain functions in general. 

FAQs (Frequently Asked Questions)

1. Explain the effect of substituents on the basicity of amines.

Nitrogen atoms having a lone pair of electrons is the prime reason for the basic nature of Amine. According to the Lewis acid-base concept, this lone pair of electrons donate making amines a Lewis base.

 

Also, according to the Bronsted- Lowry definition, Bronsted Lowry bases accept a proton. Amines contain a nitrogen atom bound to some grouping of carbon and hydrogen atoms and can make three bonds total. Amines react with acids and gain a hydrogen ion. This reaction gives Amine a positive charge.

 

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The amine can accept hydrogen atoms to act as Bronsted Lowry Base.

2. List down the application of the amines.

Below is the application of amines:

  • Amines found in products of personal care. Ethanolamines are the universal type of Amine used in the global market.

  • Serotonin is an important amine that serves as one of the primary neurotransmitters. It is critical for the speed with which the brain operates. It also controls the feelings of hunger. 

  • Analgesics like Morphine and Demerol used as painkillers comprises amines.

  • Methamphetamines and amphetamines known for recreational drugs are basic with pH greater than seven and hence neutralizes the action of acids.

  • Amines used in making azo-dyes and nylon apart from medicines and drugs. It also helps in water purification, in pest control, and leather tanning.

  • It is used in water purification. 

  • Amines are used in the development of insecticides and pesticides. 

3. What is the difference between amine and amides?

The basic difference between amines and amides is that they are different types of organic compounds. In amines no carbonyl group is attached to the nitrogen atom, while in amides a carbonyl group is always attached to a nitrogen atom.

 

Amines are derivatives of ammonia, with one or more hydrogen atoms being replaced by a substituent such as an alkyl or aryl group, and the substituents are attached to one nitrogen atom.

 

This structural difference is the reason for all other differences in their properties such as reactivity, acidity, and stability.

 

Amides are functional groups in which a carbonyl carbon atom has a single bond with a nitrogen atom, a hydrogen or a carbon atom. 

 

The formula of amine is RNH2. The formula of amide is R-CO- NH2.

4. How are amines obtained?

Aliphatic amines are generally found in nature as products of the putrefaction of the protein material. 

 

Naturally occurring amines include alkaloids (present in certain plants), the catecholamine neurotransmitters such as dopamine, norepinephrine and epinephrine, and histamine (a chemical mediator found in animal tissues). 

 

The methylamines are found in small amounts in some plants. 

 

Among the polyfunctional amines found as alkaloids in plants are atropine, morphine, cocaine, quaternary salt choline and mescaline, ethylamine or nicotine.  

 

Trimethylammonium chloride is found in nerve synapses, and in plant and animal cells.

 

But a large number of aliphatic amines are made synthetically. The most widely used industrial method is the reaction of alcohols with ammonia at a high temperature, with metals like nickel and copper, or metal oxide as catalysts. 

 

The methods of obtaining amines may be broadly divided into two groups: 

1) The Chemical reduction of members of several other classes of organic nitrogen compounds.  

2) Ammonia or amine reactions with organic compounds.

Aniline and some aromatic amines were earlier obtained from coal tar but now are synthesized from benzene or other hydrocarbons. 

5. Are amines toxic?

Most aliphatic amines are not highly toxic. In fact, most are natural components of foods and pharmaceuticals and are totally harmless.

 

In fact, those found in food are involved in producing amino acids, which are crucial to the production of protein. 

 

But in high concentrations, the smaller amines could be highly irritating to the skin and the mucous membranes of the eyes, nose, throat, and lungs. Prolonged exposure can cause acute damage to these. Larger amines are usually less irritating. 

 

Aromatic amines are also irritants that can be absorbed through the skin. They can be quite dangerous. For example, aniline is known to destroy the haemoglobin of blood and has been linked with cancer. 

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