Amines are characterised by a strong, foul odour that smells like rotting fishes. There is a huge significance of amines in our life. They are essential for life's survival because they are involved in the production of amino acids. In humans, amino acids are the building components of proteins. Amino acids are also used to produce a variety of vitamins.

 

Some uses of amines are listed below: 

 

• Amines are typically utilised in the pharmaceutical industry. Pain medicines like Morphine and Demerol contain amines in them. 

 

• Insecticides and leather tanning are two common uses for amphetamines. They are often used in synthetic dyes.

 

• Amines are also used to develop recreational drugs like methamphetamines and amphetamines. 

 

• Choline, which is an alkylammonium salt that has numerous industrial applications, helps the brain operate properly by assisting in the creation of neurotransmitters in the body.

 

• Aside from medicines and drugs, amines are also used to make azo-dyes and nylon. They are commonly used in the development of crop protection and water treatment chemicals.

 

• Amines are also used in personal care items. The most frequent type of amine used in the global market is ethanolamines.

 

Amines are classified as primary, secondary, or tertiary based on the number of hydrogen atoms substituted in the ammonia molecule (NH₃).

Primary Amines 

We represent amines with either an R or Ar for simplicity in chemistry. Primary amines are those ammonia derivatives in which only one hydrogen atom is substituted by an alkyl or aryl group. 

When one H in NH₃ is replaced by an R, the compound would become RNH2. 

Methylamine, ethylamine, and dibenzamine are some examples.

Secondary Amines

When two hydrogen atoms of ammonia are replaced by an alkyl or aryl group, we get R2NH. In other words, we get a secondary amine. Dimethylamine is an example of a secondary amine. 

Tertiary Amines

When all three hydrogen atoms are replaced by an alkyl or aryl group, then we get R3N, which is a tertiary amine. Trimethylamine is an example of a tertiary amine.

 

Some properties of amine are listed below: 

 

• The lower aliphatic amines have a distinctive "fishy" smell. They are also gaseous in nature. They are water-soluble because they can create water molecule hydrogen bonds.

 

• Primary amines are liquids at normal temperature whereas higher amines are solids at room temperature. 

 

• Aniline and other arylamines are generally colourless, but when left out in the open, they get stained owing to environmental oxidation.

 

• The amine molar weight is reduced by doubling the size of the hydrophobic alkyl component, resulting in a reduction in aqueous solubility.

 

• Undissolved amines in the soil are found at lower concentrations. Amines are easily dissolved by organic solvents like ethanol, benzene, and ether.

 

• Primary amines have a stronger intermolecular interaction than secondary amines because two hydrogen atoms are still present in primary amines. In tertiary amines, there is no intermolecular interaction because no free hydrogen is available for bonding. 

 

• As the molecular mass of the molecule increases, the boiling point of amine increases as well. The boiling point order of amines is as follows: primary amine at 48.60 °C > secondary amine at 37 °C > tertiary amine at 3.5 °C, based on intermolecular hydrogen bonding.

 

• Since the lone pair of electrons on a nitrogen atom in aromatic amines is delocalized and less accessible for acid, aliphatic amines are more basic.

 

       1. Write IUPAC names of the following compounds and classify them into primary, secondary, and tertiary amines.

 

(i) (CH3)₂ CH NH 2

 

(ii) CH₃ (CH₂)₂ NH 2

 

(iii) CH₃ NH CH (CH₃)₂

 

(iv) (CH₃)₃ CNH 2

 

(v) C₆H₅ NH CH₃

 

(vi) (CH₃ CH₂)₂ N CH₃

 

(vii) m – Br C₆ H₄ NH₂

 

Solution :

 

(i) 1 – Methylethanamine (10 amines)

 

(ii) Propan – 1 – amine (10 amines)

 

(iii) N – Methyl – 2 – methyl ethanolamine (20 amines)

 

(iv) 2 – Methylpropan – 2 – amine (10 amines)

 

(v) N – Methyl benzamine or N – methylamine (20 amines)

 

(vi) N – Ethyl – N – methyl ethanolamine (30 amines)

 

(vii) 3 – Bromobenzenamine or 3 – bromoaniline (10 amines)

 

2. Arrange the following:

 

(i) In decreasing order of basic strength in the gas phase: C₂H₅NH₂, (C₂H₅)2NH, (C₂H₅)3N and NH₃

 

(ii) In increasing order of boiling point: C₂H₅OH, (CH₃)2NH, C₂H₅NH₂

 

(iii) In increasing order of solubility in water: C₆H₅NH₂, (C₂H₅)2NH, C₂H₅NH₂.

 

(iv) In decreasing order of the pKb values:

C₂H₅NH₂, C₆H₅NHCH₃, (C₂H₅)2NH and C₆H₅NH₂

 

(v) In increasing order of basic strength:

C₆H₅NH₂, C₆H₅N(CH₃)₂, (C₂H₅)₂NH and CH₃NH₂

 

Solution: 

 

(i) In the gas phase, basicity follows the order: (C₂H₅)3N > (C₂H₅)2NH > C₂H₅NH₂ > NH₃. Because solvation does not stabilise basic strength in the gas phase, basic strength follows the predicted order based on the +I action of alkyl groups.

 

(ii) (CH₃)2NH < C₂H₅NH₂ < C₂H₅OH

The extent of H-bonding in a chemical determines the boiling point of that component. The boiling point of a compound increases as the H-bonding in the compound becomes more extensive.

 

(iii) C₆H₅NH₂ < (C₂H₅)2NH < C₂H₅NH₂

Amines are soluble in water because they may form hydrogen bonds with it. However, when the bulk of the hydrocarbon portion grows, the solubility drops.

 

(iv) Only one C₂H₅ group is present in C₂H₅NH₂, but two C₂H₅ groups are present in (C₂H₅)2NH. As a result, the +I effect in (C₂H₅)2NH is greater than in C₂H₅NH₂. (C₂H₅)2NH has a higher electron density over the N-atom than C₂H₅NH₂. Thus, (C₂H₅)2NH has a higher basicity than C₂H₅NH₂.

 

Furthermore, due to the delocalization of the lone pair in the former two, both C₆H₅NHCH₃ and C₆H₅NH₂ are less basic than (C₂H₅)2NH and C₂H₅NH₂. In addition, because of the +T effect of the CH₃ group, C₆H₅NHCH₃ will be more basic than C₆H₅NH₂. As a result, the following is the order in which the compounds' basicity increases:

 

C₆H₅NH₂ < C₆H₅NHCH₃ < C₂H₅NH₂ < (C₂H₅)2NH

 

We know that the higher the basic strength, the lower is the pKb value.

 

Therefore, the correct order is:

C₆H₅NH₂ > C₆H₅NHCH₃ > C₂H₅NH₂ > (C₂H₅)2NH

 

(v) The presence of the +I effect of two CH3 groups in C₆H₅N(CH₃)₂ makes it more basic than C₆H₅NH₂. Furthermore, CH₃NH₂ has one CH3 group, whereas (C₂H₅)2NH has two C₂H₅ groups. C2H5NH2 is thus more basic than (C₂H₅)₂ NH.

 

Due to the R effect of the C₆H₅ group, C₆H₅N(CH₃)₂ is now less basic than CH₃NH₂.

 

As a result, the basic strengths of the given compounds are listed in ascending order:

 

C₆H₅NH₂ < C₆H₅N(CH₃)₂ < CH₃NH₂ < (C₂H₅)2NH

 

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Amines play an important role in not just the industrial side of things, but it is also a compound that is essential for the very existence of life. Amines are responsible for the production of amino acids which are the building block of proteins. Protein synthesis plays a huge role in a wide variety of cellular processes. Class 12 and Class 11 students of Chemistry can find all the fundamental topics and subtopics of amines on the MSVgo app. MSVgo app also features textbook solutions. Students can find Amines NCERT solutions on the MSVgo app. Download the app now to reap its multiple benefits.