A Quick Guide To Primary Amines and Nitrous Acid

Amines are derivatives of ammonia and are basic compounds that can be influenced by various factors like the solubility of the cation to be formed or neighbouring atoms. Amines are classified based on the replacement of hydrogen atoms in NH3 molecules. When one hydrogen atom is replaced by an alkyl or aryl group, it is called primary amines. Similarly, in secondary and tertiary amines, two and three hydrogen atoms are replaced with alkyl or aryl groups, respectively.

Primary Amines

All the amines are prepared by the alkylation of alcohol from ammonia. In primary amines, one of the three hydrogen atoms is replaced by an alkyl or aromatic substituent group. For example- Methylamine= CH3NH2, where one hydrogen atom is replaced by a methyl group.

Physical properties of primary amines

• Shows some solubility in water
• The boiling point is higher than phosphines and lower than alcohol
• The hydrophobicity of the compound increases as the length of the chain increases.
• It is able to form a chemical bond.
• They are bases, and this depends on the electronic substituents.
• Primary amines solubility is high when the number of carbon atoms increases.

Chemical properties of primary amines 

• They have nucleophilicity and thus show high reactivity.
• Most of the primary amines react with metal ions to form coordination compounds, so they act as good ligands.
• The most important property is that they react with aldehydes and ketones, leading to the formation of imines. 
• A primary amine reacts with an aldehyde to form imines.

Nitrous Acid (HNO2)

Nitrous acid is a weak and unstable acid. It is found in the form of salts and esters. It is formed under cold, acidic conditions, and it decomposes to form nitric oxide (NO) and nitric acid (HNO3). The structure of nitrous acid contains two oxygen atoms to a nitrogen atom, one bonded with a single bond and the other with a double bond. In the lower atmosphere, when nitric oxide reacts with water, nitrous acid is formed naturally.

Primary amines and Nitrous acid

Nitrous acid is used to detect the presence of amines. It is a widely used technique for detecting the different types of amines. The nitrous acid is prepared in situ by acidifying amines with hydrochloric acid and then adding sodium or potassium nitrate.

When a primary amine reacts with nitrous acid, it gives a burst of colourless and odourless gas of nitrogen, confirming the presence of primary amines. The product includes an alcohol group replacing the amine group that is NH2.

Example- When ethylamine reacts with nitrous acid, its ethyl alcohol, water and nitrogen gas.

CH3CH2NH2 + HNO2 → CH3CH2OH + N2 + H2O

So the observation of colourless and odourless gas confirms the presence of primary amines.

Conclusion

Amines play an important role in biology. In humans, they play an important role as amino acids in the process of metabolism and other bodily functions. Primary amines contribute to the preparation of various drugs and medicines. The amines also act as neurotransmitters in our body, for example, serotonin. Primary amines function for the survival of life. It is the foundation of protein that, in turn, is the building block of human life.

It can control the sleep and wake-up cycles and can control the emotions of human beings. Amines are a well-studied part of chemistry, and it has so many applications in the pharmaceutical and health sectors.