Natural Sources of Aromatic Hydrocarbons and Uses

 Sources of Aromatic Hydrocarbons

The aromatic hydrocarbon compounds such as benzene were first discovered in 1825 by Michael Faraday who separated it from the oily condensate which was placed in cylinders containing compressed gas that were then used for lighting purposes. This gas is produced by the hydrolysis of whale oil.

 Benzene and other simple aromatic hydrocarbons are the main ingredients of almost all perfumes. Any aromatic compound can be made, whether laboratory or industry, from a simple computer containing a benzene ring. In addition to its use as a starter in many organisms, benzene was also widely used as a solvent. (It has now been classified as a high carcinogen). So there was a great need for these simple hydrocarbons. Their needs were met by two types of natural resources namely coal and gas.

Coal is used to produce the coke needed for smelting iron ore, as well as for other metals. In this process, coal tar is obtained as a by-product. Therefore, when coal is heated to 1000-1500 ° C in the absence of air, it produces:

(1)   A gas-fired product is known as coal gas,

(2)   A liquid substance is known as coal tar

(3)   A residue known as coke

Coal gas mainly contains hydrogen, methane, carbon monoxide, and ammonia. Coal asphalt is rich in fragrant chemicals and in isolation, provides benzene, toluene, xylenes, phenol, cresols, naphthalene, anthracene, phenanthrene, etc., in various amounts.

Although Aromatic hydrocarbons are also naturally derived from petroleum and are found in the refining of petroleum, they are produced mainly by the important modification of aliphatic hydrocarbons present in petroleum. Flexible conversion (also known as hydroforming) is performed at 500-550 ° C where there is a catalyst similar to chromium oxide based on alumina, under pressure. It may involve dehydration, such as the formation of benzene from cyclohexane, cyclization, such as the formation of benzene from n-hexane, or isomerization, such as the formation of benzene from methyl cyclopentenone.

Similarly, toluene can be produced by dehydrogenation of methylcyclohexane, cyclization of n-heptane, or isomerization of 1,2-dimethyl cyclopentane. It can be noted that sweet hydrocarbons contain the same number of carbon atoms as aliphatic hydrocarbons are found in them.

Today, petroleum is a major source of benzene, toluene, and xylenes, but benzene is found in very small amounts compared to toluene and xylenes. However, the latter can be converted to benzene by heating with hydrogen under pressure where there is a metal oxide catalyst. This process is known as hydrodealkylation. The reaction is given below: