The epoxides are aliphatic or cyclic hydrocarbons having in its structure an oxygen atom bonded to the same time to two carbon atoms. This bond, as seen in the image below, has a triangular geometry, quite characteristic for all epoxies.
Epoxides originate from alkenes that undergo double bond breaking to form the epoxide functional group. Each of the two oxygen-bonded atoms is also bonded to R 1 , R 2 , R 3, and R 4 side groups , all parts of the same molecule.
The epoxy functional group is characterized by having a high tension, which confers a reactivity greater than that of a non-cyclic ether. The reactions of epoxides are usually accompanied by the breakdown of their functional group.
The simplest epoxide corresponds to ethane epoxide, also called ethylene oxide, ethylene oxide or oxirane. Of all, this is the most commercially important epoxide.
The largest proportion of epoxy production is destined to the manufacture of paints (surface coatings). They are also used in the production of surfactants, adhesives, plasticizers, etc.
Compounds with the functional group epoxides can be named in different ways, such as: epoxy, epoxides, or other names without any systematic connotation, such as: oxirane.
Epoxides with the simplest chemical structures are often referred to as oxides. In this way, propene epoxide (C 3 H 6 ) is called propene oxide (C 3 H 6 O).
It is common for the epoxide to be named identifying the carbons that are present in the epoxide functional group. For example: 2,3-epoxyhexane, 1,2-epoxycyclohexane, and 1,2-epoxypropane. That is, the “triangle” is found at carbons 2 and 3 of hexane, and so on with cyclohexane and propane.
Ethane epoxide or ethylene oxide is prepared by the catalytic oxidation of ethylene in hot air or oxygen, using metallic silver as catalyst:
This method is carried out in two stages: a) Formation of chlorohydrin, and b) Treatment of chlorohydrin with a base to eliminate hydrochloric acid.
In step b), a molecule of HCl is lost, the hydrogen of which comes from the OH group.
Carbon-carbon double bond peroxidation
Epoxides can also be formed by the peroxidation of alkenes, that is, an oxidation caused by a peroxyacid, such as peroxybenzoic acid:
Natural presence of epoxides
Epoxies are rare in nature. However, hepatic synthesis of epoxides, mediated by cytochrome P450, has been observed. Cells produce epoxides as oxidation products of alkenes and aromatic compounds.
Compounds such as epothilones, produced as a secondary metabolite of the bacterium Sorangium cellulosum, have also been observed in nature.
Manufacture of surfactants
Ethylene oxide is frequently used in the preparation of surfactants or surfactants, products of the reaction of an alcohol or phenol with ethylene oxide. Surfactants serve different functions, including: humectants, detergents, emulsifiers, and solubilizers.
Moisturizers increase the hydration of surfaces by facilitating the access of water to them. Detergents remove dirt from clothes. Emulsifiers allow and stabilize emulsions. And solubilizers allow the dissolution of compounds that are poorly miscible with water.
Adhesives and solvents
The reaction of epoxides, including ethylene oxide, with amines is the basis for the preparation of glues or glue. These adhesives are used to bond surfaces as well as stabilize PVC.
Ethylene oxide reacts with sodium ethoxide to produce 2-ethoxyethanol, also known as Cellosolve. This chemical compound dissolves oils, resins, fats, waxes, nitrocellulose and lacquers.
Epoxy or epoxy resins have among their properties, once they have been reinforced, a high chemical, thermal and mechanical resistance. These resistors allow its use for the production of lacquers and enamels, as well as for the coating of metals and laboratory floors and the manufacture of electrical parts.
Some companies use these silica-filled resins as a substitute for porcelain to make power line insulators. Epoxy resins are also used to make glass fiber reinforced boards and printed circuit boards.
Epoxy resins separately have few uses, including increasing the stability of vinyl. To increase their usefulness, they are cross-linked with various compounds in a process known as “curing.” Among the agents used for this purpose we have: primary, secondary, tertiary amines, and polyamides.
The epoxides obtained from vegetable oils are used for the synthesis of polyols, used in the polyurethane industry.
Epothilones are metabolic products of the bacterium Sorangium cellulosum, which have the property of stabilizing microtubules, thus producing a blockage of the cell cycle.
Ixabepilone, an epothilone, has been approved for the treatment of advanced breast cancer. Likewise, the use of epothilone D in the treatment of Alzheimer’s has been studied.
Ethylene oxide is involved in the synthesis of ethylene glycol: a compound used as antifreeze in automobile cooling systems. Ethylene oxide is also used in the sterilization of medical materials and instruments.
Absorption through the skin, inhalation or ingestion of epoxides are associated with the production of toxic effects, both in man and in experimental animals. These include: irritation of superficial tissues and sensitization. Alterations also occur in liver function, blood cells and bone marrow.
Likewise, epoxides have been associated with carcinogenicity and mutagenicity. Epoxides, due to their high electrophilic reactivity and their character as alkylating compounds, have been considered as potential carcinogenic agents.
Examples of epoxies
Finally, some other examples of epoxides will be listed:
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- Morrison and Boyd. (1987). Organic chemistry . (Fifth edition). Addison-Wesley Iberoamericana.
- Wikipedia. (2020). Epoxide. Recovered from: en.wikipedia.org
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- Manson MM (1980). Epoxides: is there a human health problem? British journal of industrial medicine , 37 (4), 317–336. doi.org/10.1136/oem.37.4.317
- Chemicals. (sf). Examples of Epoxides. Recovered from: quimicas.net
- WG Potter. (1963). The Chemistry and Uses of Epoxide Resins, Occupational Medicine, Volume 13, Issue 1, April 1963, Pages 42–47, doi.org/10.1093/occmed/13.1.42
- Molinero Muñoz, María and Fernández Arberas, Nerea. (2016). Epothilones, an alternative in the field of antitumor drugs. Complutense University Madrid.
- Alejandro Aguirre F. & Lesly Espinoza B. (2018). Uses and applications of epoxy ethers and sulfides. Central University of Ecuador. Recovered from: academia.edu