In 1825, Michael Faraday began a number of experiments in distillation. Among the products which he worked on was crude oil, from which he extracted a gas. Out of mere curiosity, he set it alight and the gas burned. For many years, the benefits of what Faraday called "bicarburet of hydrogen" were unknown. In 1846, A. W. Hoffman isolated the same product, later called benzene, in large quantities by distilling coal. For a long time, benzene could only be extracted from coal; however, with the rise of oil exploitation, its importance increased significantly. From the dawning of the twentieth century, benzene (C6H6), a volatile, colourless and flammable hydrocarbon, saw extraordinary growth in its applications in an abundance of fields. The varied properties of benzene grant it importance industrially and, at the same time, inspire great theoretical interest.
Faraday probably had no idea that his "bicarburet of hydrogen" would long remain an enigma to chemists.
In 1865, to explain the properties of benzene, the German chemist August Kekulé, proposed a hexagonal structure with an atom of carbon and an atom of hydrogen at each corner with alternate double and single bonds between carbon atoms.
Shortly after Kekulé's theory was established, the London Chemical Society proclaimed it to be "the most brilliant piece of scientific production to be found in the whole of Organic Chemistry", because it served as a new imaginative outlook in chemistry.
Benzene is one of the first chemicals in history whose unique properties were studied by chemists.
In 1931, Linus Pauling used quantum physics to propose that benzene contained a hybrid structure.
This innovation suggested that benzene contained delocalized electrons (as shown in the diagram).
Furthermore, this hybridization in benzene makes the molecule more stable than it would be if it had localized bonds.
This extraordinary stability is important in benzene's many chemical applications.
The long battle to discover the true structure of benzene ended in 1931. However, along this path, the study of structural chemistry greatly increased due to these innovations, and at the same time modern chemists were inspired to continue to advance chemical technology to greater lengths.
Prior to World War One, the primary application of benzene was in gasoline blending, because it enhanced the octane number in gasoline. Benzene was also widely used as a solvent by many large scale chemical manufacturers.
In the midst of World War Two, benzene was also employed in the chemical industry.
Today's organic chemistry industry is based almost entirely on chemicals derived from petroleum, of which benzene play a significant role.
Benzene is a precursor to many important chemical intermediates, including drugs, dyes, insecticides and plastics.
The principal commercial uses for benzene, at present, include the manufacture of ethylbenzene, cumene and cyclohexane.
Benzene can be alkylated with ethylene to give ethylbenzene, which can be converted to styrene, producing polystyrene plastics and synthetic rubber.
Hence, these products give us applications in rubbers, paints, panels and toys.
Benzene can also be alkylated with propylene to yield cumene, which is processed to create phenol.
This product can be used to make telephone parts, adhesives and dyes for fabrics, wood or paper.
Hydrogenation of benzene yields cyclohexane, which can be oxidized to forms adipic acid, from which is produced the universally applied fabric of nylon (also in the Chemistry Hall of Fame) and otehr polyamides.
Industrial applications on a smaller scale using benzene intermediates include aniline which is used to make dyes and plastics. Benzene is also commonly chlorinated to yield various chlorobenzenes, put to use in such products as moth flakes, or alkylated to produce alkylbenzenes, used to manufacture various detergent products.
The wonderful innovation of the benzene ring puts any substance possessing it into a very broad organic family known as the aromatic compounds. The number of chemical structures which include the benzene ring are almost immeasurable. Some common items which include the benzene ring range from wood preservatives to Aspirin, the world's best known pain reliever (also in the Chemistry Hall of Fame), to oilf of wintergreen, a commonly used fragrance.
Thus, benzene, the simplest aromatic compound, finds applications in an abundance of fields. Without a doubt, the industrial community relies on benzene to produce commodities utilized in our everyday life, and at the same time benzene provides modern chemists with the inspiration to bring the field of chemistry to new and greater lengths, just as Kekulé and Pauling had accomplished in the past.
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