Preparation and Uses of Aromatic Compounds

The compounds which follow the principle of aromaticity are known as aromatic compounds. The rule for aromaticity is given by a renowned German scientist Erich Huckel. The rule came to be known as the Huckel rule of aromaticity. According to the Huckel rule of aromaticity, the planar closed chain molecule is aromatic when it contains (4n+2) delocalised electrons. Here ‘n’ is a non-negative integer. Compounds which do not follow huckel’s rule are not aromatic, they are also divided into two classes- non-aromatic and anti-aromatic, These are distinguished by using some other simple rules, for e.g. the only difference between aromatic and anti-aromatic compounds is that aromatic compounds have (4n+2) delocalised electrons, while anti-aromatic have 4n delocalised electrons, rest all rules stand the same for both. Aromatic compounds are also known as arene compounds. The aromatic compounds are called aromatic compounds because they give out an aroma on their exposure to the environment. There are several compounds which provide aroma. In organic chemistry, the most widely used aromatic compound is Benzene. The molecular formula of Benzene is C₆H₆.

The aromatic hydrocarbons are classified into two categories:

• Benzenoid Aromatic Hydrocarbons
• Non-Benzenoid Aromatic Hydrocarbons

Benzenoid Aromatic Hydrocarbons

Benzenoid aromatic hydrocarbons are aromatic hydrocarbons that contain Benzene rings in their structural molecules.

For instance: Di-phenyl

Non-Benzenoid Aromatic Hydrocarbons

Non-Benzenoid aromatic hydrocarbons are aromatic hydrocarbons and do not contain Benzene rings in their structural molecules. For such compounds, the aromaticity is due to unsaturation in the compound itself and is thus known as Non-Benzenoid Aromatic Hydrocarbons.

For instance: pyridine

Preparation of Aromatic Hydrocarbons

1)  Polymerisation of Alkynes

The aromatic hydrocarbon, mainly Benzene, can be manufactured by polymerising the alkyne. When three moles of ethyne pass through a red hot iron tube called Fe-tube, an aromatic compound known as Benzene is formed. This is also one of the major laboratory methods used for the production of Benzene. The temperature involved in the process is around 873K. The reaction can be represented as,

3CHCH  →  C₆H₆

2) Reduction of Phenols

Benzene can also be obtained when phenol, also known as hydroxy-benzene, undergoes a reduction process using an element called zinc. The process is known as the reduction process through which phenol gets converted into a Benzene ring. It can be represented as,

C₆H₅-OH + Zn  →  C₆H₆ + side products

3) Decarboxylation of Acid

The Benzene ring can be obtained by decarboxylation of the benzoic acid in sodium hydroxide and calcium oxide. The process is known as decarboxylation of acid. Here sodium hydroxide acts as a base. The reaction can be represented as,

C₆H₅-COOH + NaOH + CaO →  C₆H₆ + side products

Uses of Aromatic Hydrocarbons

The uses of aromatic hydrocarbons are mentioned as,

1. Aromatic Hydrocarbons are organic compounds that are planar in structure and follow the Huckel rule of aromaticity. They are non-polar, and thus they act as a non-polar solvent for a large number of non-polar solutes.
2. Aromatic compounds are used as additives in various industries like petroleum and gas. Aromatic compounds are used in gasoline and petroleum as fuel additives.
3. Aromatic compounds are also non-reactive. Therefore they are used in paints and lacquers. Aromatic toluene is used as a solvent in the paint industry for thinners and paint removal.
4. The aromatic compounds are also used in the production of chemicals. Aromatic compounds can be used in the production of fertilisers and pesticides.
5. Naphthalene, a fused product of two Benzene rings, is used as a pesticide and insecticide in homes and workspaces.
6. Anthracene is used as a building block of the dye industry. It is used for the production of preservatives for wood.
7. Benzene Hexa-chloride is used in the pharmaceutical industry to produce medicines and syrups.

Conclusion

The aromatic compounds are those compounds that follow Huckel’s rule of aromaticity. According to the Huckel rule of aromaticity, a compound is aromatic when it is cyclic, It contains (4n+2) electrons in the ring, delocalised throughout the structure. The aromatic compound can be subdivided into the benzenoid and non-benzenoid aromatic compounds. The aromatic compounds which contain Benzene rings are known as benzenoid aromatic compounds.

In contrast, the compounds which do not contain Benzene rings and are aromatic are known as non-benzenoid aromatic compounds. Aromatic compounds are used in different industries like the gasoline industry, petroleum industry, paint industry, pesticide industry etc. Aromatic compounds are sweet-smelling and are also used in perfumes and deodorants.

Basics of aromaticity must be cleared before diving deeper into the concepts and working on equations involving aromatic compounds.