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Ethylene

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Ethylene, also known by its IUPAC name ethene, is a colorless and highly flammable gas. It possesses a faint, sweet, and musky odor when it is in a pure state. Chemically, ethylene is a hydrocarbon, which is a molecule composed of carbon and hydrogen atoms. It is classified as the simplest alkene. An alkene is a type of hydrocarbon that contains at least one carbon-carbon double bond. This double bond is a critical feature of the molecule. It creates a region of high electron density. This density makes the molecule very reactive, meaning it easily undergoes chemical changes.

The structure of ethylene is quite simple and elegant. It consists of four hydrogen atoms bound to two carbon atoms. These two carbon atoms are connected by a double bond. All six atoms in the molecule lie on the same flat plane. The angle between the hydrogen and carbon atoms is 117.4 degrees. This is very close to the ideal 120-degree angle for its specific atomic arrangement. The double bond is also somewhat weak. If you supply heat at 50 degrees Celsius, the bond can rotate. This rotation requires breaking the pi-bond, which is one part of the double bond. This specific pi-bond is what makes ethylene so useful in chemical reactions.

Industrial production of ethylene happens on a massive scale. In 2022, global production exceeded 225 million tonnes. This makes it the most produced organic compound in the world. One primary method for making it is called steam cracking. In this process, hydrocarbons and steam are heated to temperatures between 750 and 950 degrees Celsius. This intense heat breaks large hydrocarbon molecules into smaller ones. If ethane is used as the starting material, ethylene is produced. In Europe and Asia, producers often crack naphtha, gasoil, or condensates. This method also produces other useful chemicals like propylene. After cracking, the ethylene is separated from the mixture using compression and distillation. Other methods include methanol-to-olefins and Fischer-Tropsch synthesis.

Ethylene is used to create a vast array of essential products. The largest use is polymerization, which accounts for more than half of the global supply. Through polymerization, ethylene is turned into polyethylene. Polyethylene is the most widely used plastic on Earth. It is used to make packaging films, carrier bags, and trash liners. Another major use is oxidation. This process creates ethylene oxide, a key material for making detergents and surfactants. Ethylene oxide can also be turned into ethylene glycol, which is used as automotive antifreeze.

C2H4uses
C2H4uses

Other chemical reactions involve ethylene in several different ways. Through halogenation, ethylene reacts with halogens to create intermediates like ethylene dichloride. This chemical is a precursor to polyvinyl chloride, a common plastic. Alkylation is another process that produces ethylbenzene. Ethylbenzene is used to make styrene, which is used for insulation and polystyrene packaging. Styrene is also used to make the rubber found in tires and footwear.

Uses of Ethene
Uses of Ethene

Ethylene can also undergo hydration to produce ethanol. Since the mid-1990s, this has been done using direct hydration with solid acid catalysts. Even more specialized reactions, like the oxo reaction, produce propionaldehyde for various industrial uses.

Humans have been discovering the properties of ethylene for centuries. Johann Joachim Becher is believed to have discovered the gas in 1669. He produced it by heating ethanol with sulfuric acid. In 1795, a group of four Dutch chemists studied the gas in detail. They discovered it contained both carbon and hydrogen. They also found it could produce oil when combined with chlorine. Because of this, they called it "olefiant gas." This name is the origin of the modern term "olefin."

Uses of Ethene
Uses of Ethene

The name ethylene itself became common by 1852. While the official IUPAC name is ethene, the name ethylene remains very popular in the North American chemical industry.

Beyond the factory, ethylene plays a vital role in the natural world. It acts as a natural plant hormone. This means it serves as a chemical signal that tells plants how to grow. Ethylene specifically controls the ripening of fruits and the flowering of plants.

Dewar-Chatt-Duncanson model
Dewar-Chatt-Duncanson model

In agriculture, farmers use ethylene to manage how quickly fruit ripens. Conversely, they can use "scrubbing" to remove ethylene and delay ripening to keep fruit fresh longer. In a much more specialized niche, ethylene was once used as an anesthetic. Researchers at the University of Chicago studied its use for this purpose. However, because it is explosive and has a pungent odor, it is rarely used as an anesthetic today. Ethylene remains a fundamental link between biology and global industry.

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File:C2H4uses.png
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File:Rh2Cl2 C2H4 4.svg
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