Ethylene Glycol(redirected from Dihydroxyalcohol)
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glycol (glīˈkōl), dihydric alcohol in which the two hydroxyl groups are bonded to different carbon atoms; the general formula for a glycol is (CH2)n(OH)2. The most important glycol is the simplest, ethylene glycol, or 1,2-ethanediol, CH2OHCH2OH, a slightly sweet-tasting, somewhat viscous liquid that is miscible with water. Because of its low volatility (b.p. 197℃) and low corrosive activity, it is widely used in mixtures of automobile antifreeze. Ethylene glycol can be esterified to form polyesters, e.g., Dacron, and can be nitrated to form an explosive used in mining. It is prepared commercially by oxidation of ethylene at high temperature over a silver oxide catalyst, followed by acid-catalyzed hydrolysis of the ethylene oxide that is formed.
Cellosolves (e.g., methyl cellosolve, CH3OCH2CH2OH) are monoether derivatives of ethylene glycol. They are excellent solvents, having solvent properties of both ethers and alcohols; they have other uses as well. Polyethylene glycol (PEG) is used to thicken shampoo and cosmetics. It can also be attached to other molecules via a process called pegylation. When pegylated to medicinal drugs, it can alter their distribution in the body, metabolism, and excretion. Such alteration can lead to improved dosing intervals and may also have beneficial effects on safety and efficacy. Pegylation can also mask certain drugs, such as interferon, from the immune system, preventing their rejection.
(also 1,2-ethanediol), HOCH2CH2OH, the simplest of the glycols.
Ethylene glycol takes the form of a colorless, viscous liquid with a sweet taste. It has a melting point of – 12.3°C, a boiling point of 196°C, and a density of 1.113 g/cm3 at 20°C. Miscible in all proportions with water, alcohol, and acetone, it is poorly soluble in ether and insoluble in chloroform, aliphatic hydrocarbons, and aromatic hydrocarbons. Ethylene glycol is hygroscopic.
An important property of ethylene glycol is its capacity to produce a marked lowering of the freezing point of water. A 40-percent solution of ethylene glycol in water has a freezing point of – 25°C, and a 60-percent solution has a freezing point of – 40°C. For this reason, ethylene glycol is commonly used in the manufacture of antifreezes.
Similar to other dihydric alcohols, ethylene glycol forms monoglycolates and diglycolates (such as HOCH2CH2ONa and NaOCH2CH2ONa), ethers, and esters. Among the other derivatives of ethylene glycol are cellusolves (the monoethers HOCH2CH2OR, where R is a hydrocarbon) and polyesters, including polyethylene terephthalate, that have the general formula (—OCH2CH2OCO—R—CO—)n; cellosolves are used as solvents, and ethylene glycol polyesters are used in the preparation of Dacron and similar synthetic fibers (seeLAVSAN and POLYESTER FIBER). Nitroglycol, a diester of ethylene glycol and nitric acid, is an explosive.
The principal industrial method for the production of ethylene glycol is the hydration of ethylene oxide at a pressure of 10 atmospheres and a temperature of 190°-200°C (or at 1 atmosphere and 50°-100°C) in the presence of 0.1–0.5 percent sulfuric or ortho-phosphoric acid; diethylene glycol and a small quantity of higher polymeric homologues of ethylene glycol are formed as by-products in this process. Ethylene glycol is used on a limited scale as a solvent for printer’s inks and certain other dyes, and it is used in the production of various inks, including inks for ball-point pens. It is also used in organic synthesis. Ethylene glycol is toxic.
M. K. GRACHEV