Preparation and Uses of Aromatic Hydrocarbons

The chapter contains a brief introduction of aromatic compounds, along with its examples, preparation methods, uses, FAQ’s and other relevant information. Check out more about aromatic hydrocarbons.

Introduction

Aromatic compounds refer to unsaturated chemical compounds consisting of single or multiple rings with delocalized pi-electrons. They are also known as arenes or aryl compounds. Aromatic compounds derive their name from their fragrance or odour. These compounds have several unique characteristics that stand out among other organic substances. Due to its unique properties, it has several important industrial and other uses. The compounds are commercially prepared with the help of petroleum or coal tar. However, we can use different methods to prepare aromatic compounds in the laboratory. We will be discussing further the same in the upcoming sections.

What are Aromatic Hydrocarbons?

Aromatic hydrocarbons are primarily made of carbon and hydrogen atoms. The first compound to be recognized as an aromatic hydrocarbon was benzene. In simpler terms, we can also consider aryl hydrocarbons as a group of benzene and its derivatives. Other than benzene, aromatic hydrocarbon examples include toluene, pyrimidines, purines etc. Aryl hydrocarbons are known to be unique because of their odour. These compounds have a smell to them. For example, benzene emits a sweet smell. Earlier, it was not unusual for scientists to smell or taste the compounds to identify them.

Hence, scientists named this particular class of the compounds as aromatic when they noticed the fragrance. Aromatic compounds are broadly divided into two categories – Benzenoids and Non-Benzenoids. The aromatic compounds that consist of at least one benzene ring are known as benzenoids. On the other hand, the aromatic compounds without a benzene ring are known as non-benzenoids. The majority of the aromatic hydrocarbons come into the former category.

That is because most of them retain the benzene ring even after several chemical reactions.

Some of the properties of aromatic compounds include the extra stability of the compound because of the resonance. The delocalization of pi-electrons provides unusual stability to the ring. Also, these compounds have a comparatively higher carbon to hydrogen atom ratio. As a result, aromatic compounds give out a solid and sooty yellow flame on being burnt.

Methods of Preparation

As mentioned in the beginning, the aromatic hydrocarbons are prepared mainly by isolation of coal tar for commercial purposes. But, we can also obtain these compounds in the laboratory through some particular methods of chemical reactions. Benzene is considered the parent compound of all the other aromatic hydrocarbons. We will get an aromatic hydrocarbon if we can obtain benzene or some of its derivatives. A few methods for the preparation of aromatic compounds have been mentioned below:

Cyclic Polymerization of Alkynes: The cyclic polymerization reaction is one of the most significant reactions in the case of alkynes. It was the first method used to synthesize benzene. Acetylene is passed through a red hot tube at a high temperature of 873K to obtain benzene. It is the cyclic polymerization of ethyne. Other alkylbenzenes can be obtained by similar polymerization of other alkynes

Decarboxylation of Aromatic Acids: When benzoic acid or its derivative is heated with soda lime or CaO, it produces aromatic hydrocarbons

Reduction of Diazonium Salts: When diazonium compounds such as benzene diazonium chloride are reacted with (H₃PO₂ + CuCl) or Na₂SnO₂ (sodium stannite), we get aromatic hydrocarbons as a result

Reduction of Phenol: When phenol goes under a reduction reaction with the help of extremely heated Zinc dust, we obtain benzene. Several other methods like Wurtz-Fittig reaction, Grignard reaction, and de-sulphonation of benzene sulphonic acid can help us obtain aromatic hydrocarbons

Uses of Aromatic Hydrocarbons

Aromatic hydrocarbons have various properties that make them useful for biological processes and industrial and commercial uses. Therefore, it is used extensively in different kinds of industries. Some of those uses have been discussed below:

Due to its low reactivity and other characteristics, aromatic compounds act as efficient non-polar solvents. Therefore, it is used as additives in paints, gasoline, etc. Methylbenzene is used as a solvent in model glues

The chlorophyll (the green pigment found in plants) also contains aromatic hydrocarbons, which play a vital role in photosynthesis

If we talk about humans, the amino acids and the nucleic acids present in our bodies also contain aromatic hydrocarbons

A significant aromatic hydrocarbon, trinitrotoluene or TNT, is used as an explosive in preparation for other explosives

Aromatic hydrocarbons are also extensively used for industrial purposes. They are often used in the petrochemical industry or plastic industry

It is used in several other industries and has a wide range of applications. For instance, aromatic compounds are used for manufacturing drugs and dyes

Another aromatic compound named naphthalene is used as mothballs and often helps store and preserve clothes and other stuff