Ethylene

Ethylene or ethene is an organic chemical compound made up of two carbon atoms linked by a double bond. It is one of the most important chemical products in the chemical industry, being the most widely used organic compound in the world. Almost 60% of its industrial production is used to obtain polyethylene.

Structure

The molecule cannot rotate around the double bond and all the atoms are in the same plane. The angle between the two carbon-hydrogen bonds is 117°, very close to the 120° corresponding to sp² hybridization.

Chemical reactivity

The double bond region is relatively rich in electron density (it is a nucleophilic center) and can react with electrophiles (electron deficient) through addition reactions. Through this type of reaction, halogenated derivatives can be synthesized.

Water can also be added (hydration reaction) to give ethanol; an acid such as sulfuric acid or phosphoric acid is used as a catalyst. The reaction is reversible.

At high pressures and with a metal catalyst (platinum, rhodium, nickel) it can be reacted with molecular hydrogen to give ethane.

Production

World production of ethylene was more than 150 million tons in 2016.

Most of the ethylene produced worldwide is obtained by steam cracking (steam cracking) refinery hydrocarbons (ethane, propane, naphtha and diesel, mainly). Ethylene is also obtained from the catalytic reforming of naphthas or from natural gas (Oxidative Coupling of Methane, OCM). It can also be obtained in Organic Chemistry laboratories through the dehydration of alcohols.

Industrial process

Ethylene is produced in the petrochemical industry through cracking, dehydrogenating ethane. In this process, gaseous or light liquid hydrocarbons are heated, using furnaces, up to 750–950 °C. This high temperature causes the bonds to break, so the formation of ethylene is accompanied by the creation of other unwanted by-products, which are later separated by distillation or absorption.

Ethylene as a plant hormone

Ethylene is the phytohormone responsible for stress processes in plants, as well as fruit ripening, as well as leaf and flower senescence and fruit abscission. The famous phrase that "a bad apple spoils the basket" has its scientific foundation precisely in ethylene, since, when a ripe fruit releases ethylene, it accelerates the ripening of the fruits that surround it.^{[citation needed]} For this reason, This is why this gas is used artificially in fruits that have been harvested while still green to ripen them or to intensify the red color in tomatoes.^{[citation needed]} The ethylene that Apples give off also makes carrots taste bitter, so they should not be stored together.^{[citation needed]}

Biosynthesis

Ethylene is biosynthesized from S-Adenosyl methionine (SAM), which forms an intermediate, 1-aminocyclopropylcarboxylate acid, by action of the enzyme 1-Aminocyclopropane-1-carboxylate synthase (EC 4.4.1.4). Subsequently, the intermediate is oxidized by the action of oxygen and the enzyme aminocyclopropanecarboxylate oxidase (EC 1.4.17.4), which uses ascorbic acid as a cofactor, giving ethylene, hydrocyanic acid and carbon dioxide as products.

History

Some geologists and scholars believe that the famous Greek Oracle of Delphi (the Pythia) entered her trance state as a result of ethylene rising from fault lines in the ground.

Ethylene seems to have been discovered by Johann Joachim Becher, who obtained it by heating ethanol with sulfuric acid; he mentioned the gas in his work Physica Subterranea (1669). Joseph Priestley also mentions the gas in his work Experiments and observations relating to the various branches of natural philosophy: with a continuation of the observations on air (1779), where he reports that Jan Ingenhousz saw ethylene synthesized in the same way by a Mr. Enée in Amsterdam in 1777 and that Ingenhousz later produced the gas himself. The properties of ethylene were studied in 1795 by four Dutch chemists, Johann Rudolph Deimann, Adrien Paets van Troostwyck, Anthoni Lauwerenburgh and Nicolas Bondt, who discovered that it was it differed from hydrogen gas and that it contained both carbon and hydrogen. This group also discovered that ethylene could be combined with chlorine to produce the Dutch chemists' oil, 1,2-dichloroethane; this discovery gave ethylene the name used for it at the time, gas olefiante (gas for making oil)] The term olefiante gas is in turn the etymological origin of the modern word "olefin", the class of hydrocarbons of which ethylene is the first member[citation needed].

By the mid-19th century, the suffix -ene (an ancient Greek root attached to the end of female nouns meaning "daughter of") was widely used to refer to a molecule or part of it containing one less hydrogen atom than the molecule being modified. Thus, ethylene (C2H4) was the "daughter of ethyl" (C2H5). The name ethylene was used in this sense as early as 1852.

In 1866, the German chemist August Wilhelm von Hofmann proposed a system of hydrocarbon nomenclature in which the suffixes -ane, -ene, -ine, -one, and -une were used to designate hydrocarbons with 0, 2, 4, 6 and 8 hydrogens less than its parent alkane.. In Hoffman's system the name should be ethene and not ethylene. Hofmann's system eventually became the basis for the Geneva nomenclature approved by the International Congress of Chemists in 1892, which remains the core of the IUPAC nomenclature. However, by then, the name ethylene was very entrenched and is still widely used today, especially in the chemical industry.

Following experiments by Luckhardt, Crocker, and Carter at the University of Chicago, ethylene was used as an anesthetic, and it remained in use until the 1940s, even as chloroform was being phased out. Its pungent odor and explosive nature limit its use today.