Ethylene glycol . Also known as 1,2-ethanediol, ethylene glycol or simply glycol is the simplest diol. It was first prepared by Wurtz in 1859 and is used as an antifreeze agent in the car’s cooling system .
Summary
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- 1 Obtaining
- 2 Features
- 3 Physical properties
- 4 Chemical properties
- 1 Oxidation
- 5 Applications
- 6 Glycol
- 7 Health effects
- 8 Environmental effects
- 9 Sources
Obtaining
It was first obtained in [1859] by the French chemist Charles-Adolphe Wurtz (1817-1884). He prepared the first ethylene glycol in 1856. He first treated “ethylene iodide” (C 2 H 4 I 2 ) with silver acetate, and then hydrolyzed the resulting “ethylene diacetate” with potassium hydroxide . Wurtz named his new compound “glycol” because it shared qualities with both ethyl alcohol (with one hydroxyl group) and glycerin (with three hydroxyl groups). In 1859 Wurtz prepared ethylene glycol through hydration of ethylene oxide.
It is obtained by adding water to ethylene oxide. In the industrial manufacturing process, ethylene oxide is reacted with excess water to avoid the formation of polymers (10 times in molar excess), according to the following chemical equation:
C 2 H 4 O + H 2 O → HOCH 2 CH 2 OH
This reaction can be catalyzed by acids or bases, or it can occur at a neutral pH at elevated temperatures. The highest production of ethylene glycol is achieved with an acidic or neutral pH in the presence of abundant water. Under these conditions, a productivity of 90% can be obtained. The main by-products obtained are diethylene glycol, triethylene glycol, and tetraethylene glycol.
It can be obtained by treating 1,2-dibromoethane with silver acetate to give ethylene glycol diacetate, which is then hydrolyzed to ethylene glycol.
Ethylene glycol was first used industrially in place of glycerol during World War I as an intermediate for explosives (ethylene glycol dinitrate), but has since become an important industrial product.
The global capacity for the production of ethylene glycol through the hydrolysis of ethylene oxide is estimated at around 700 tons per year.
characteristics
Ethylene glycol is an organic chemical compound that belongs to the group of diols. It is a clear, colorless, odorless liquid with a sweet taste . It is hygroscopic and completely miscible with many polar solvents, such as water, alcohols, glycol ethers, and acetone . However, its solubility is low in nonpolar solvents, such as benzene , toluene , dichloroethane , and chloroform .
Its name derives from the Greek glycos (sweet) and refers to the sweet taste of this substance. For this property it has been used in fraudulent actions trying to increase the sweetness of the wine without the additive being recognized by the analyzes that looked for added sugars. However, it is toxic and causes kidney dysfunction.
At room temperature it is not very volatile, but it can exist in the air as vapor . It is made from the hydration of ethylene oxide (carcinogenic epoxide).
Physical properties
- Boiling point at 101.3 kPa 197.60 ºC
- Melting point -13.00 ºC
- Density at 20 ºC 1,1135 g / cm3
- Refractive index, nD20 1.4318
- Heat of vaporization at 101.3 kPa 52.24 kJ / mol
- Heat of combustion 19.07 MJ / kg
- Critical temperature 372ºC
- Critical volume 6515.73 kPa
- Critical pressure 0.186L / mol
- Flash point 111ºC
- Ignition temperature 410ºC
- Lower explosive limit 3.20 vol%
- Upper explosive limit 53vol%
- Viscosity at 20 ºC 19.83 mPa • s
- Cubic coefficient of expansion at 20ºC 0.62 × 10-3 K-1
Ethylene glycol is difficult to crystallize; when cooled, a highly viscous, subcooled mass forms, which eventually solidifies to produce a glass- like substance .
Chemical properties
Like other alcohols, ethylene glycol undergoes the typical reactions of its hydroxyl groups. Here we will only consider the special chemical characteristics and industrially important reactions of ethylene glycol. The two adjacent hydroxyl groups allow cyclization, and polycondensation; one or both of these functional groups can, of course, also react to give other derivatives.
Oxidation
Ethylene glycol is easily oxidized by oxygen , nitric acid , and other oxidizing agents to form a number of aldehydes and carboxylic acids. Typical products derived from alcoholic functions are glycol aldehyde (HOCH 2 CHO), glyoxylic acid (HOCH 2 COOH), glyoxal (CHOCHO), glyoxylic acid (HCO-COOH), oxalic acid (HOOCCOOH), formaldehyde (HCHO) and formic acid (HCOOH).
Variation of reaction conditions can lead to selective formation of a desired oxidation product.
Oxidation in the gas phase with air in the presence of copper catalysts is of industrial importance for the production of glyoxal. Glycol cleavage occurs in acidic solution with certain oxidizing agents such as permanganate, periodate, or lead tetracetate . The cleavage of the CC bond produces mainly formaldehyde , part of which is further oxidized to formic acid.
Applications
Ethylene glycol is primarily used as an antifreeze in automotive radiators as a heat diffuser, mixed with water for de-icing and anti-icing procedures on commercial aircraft, to manufacture polyester compounds, and as a solvent in the paint and plastic industry .
It is also an ingredient in photographic developing liquids, hydraulic brake fluids and in dyes used in stamp pads, ballpoint pens, and printing shops and as a raw material for the manufacture of polyester fibers.
The widespread use of ethylene glycol as an antifreeze is based on its ability to reduce the freezing point when mixed with water. The physical properties of water-ethylene glycol mixtures are therefore extremely important.
It is used in solutions to de-ice planes and ships .
It has great use as a raw material for the manufacture of polyester fibers .
Glycol
Glycols (HO-CH 2 CH 2 -OH) are a type of chemical compound that contains two hydroxyl groups (-OH groups) that result from the reaction of water with ethylene oxide. In general, all glycols come in the form of a clear, transparent, odorless, low volatility liquid.
Glycol was first used industrially in place of glycerol during World War I as an intermediate for explosives (ethylene glycol dinitrate), but has since become an important industrial product.
The global capacity for the production of ethylene glycol through the hydrolysis of ethylene oxide is estimated at around 700 tons per year.
In the flexible polyurethane industry these products have a general name and are called polyol. Glycol is used as an antifreeze additive for water in internal combustion engine radiators, it is the main compound of vehicle brake fluid and it is also used in chemical processes such as the synthesis of polyurethanes, of some polyesters, as a product of starting in the synthesis of dioxane, the synthesis of glycol monomethylether or glycol dimethyl ether, as a solvent, etc.
Health effects
Ingesting very high amounts of ethylene glycol can be fatal, while minimal amounts can cause nausea, seizures, trouble speaking, disorientation, and heart and kidney problems . Female animals that suffered from this poisoning by large amounts of ethylene glycol had offspring with birth defects, while male animals experienced a decrease in sperm count. However, these effects were observed at very high levels and are not expected to occur in people exposed to lower levels at hazardous waste sites.
Ethylene glycol affects the chemistry of the body by increasing the amount of acid, which produces metabolic problems. Poisoning presents as depression of the central nervous system and irritation at the site of absorption initially, followed by metabolic acidosis and hypocalcemia.
It can cause deafness, blindness and can leave large brain sequelae, and in large doses cause death.
It is an organic solvent with nephrotoxic activity as mentioned above. It can cause acute tubular necrosis that, if not treated in time, can lead to chronic kidney failure and later death.
If absorbed by the digestive tract, it causes intoxication and can lead to vomiting, hyperventilation, metabolic acidosis, cardiovascular dysfunction and acute kidney failure.
Environmental effects
The ethylene glycol used for aircraft de-icing is discharged directly into the environment. A report prepared by the World Health Organization in 2015 showed toxic effects on aquatic organisms exposed in the laboratory to a stream of water from an airport sewer .
Field studies in the vicinity of an airport also show toxic signs consistent with ethylene glycol poisoning, fish death, and reduced biodiversity, although these effects cannot be attributed with complete certainty to ethylene glycol.
The biodegradation process of glycols also increases the risk for organisms, as oxygen levels are depleted in surface waters. Another study found relatively low toxicity to aquatic organisms, but the oxygen-depleting effect turns out to be more severe.
Furthermore, “anaerobic biodegradation can also release relatively toxic by-products, such as acetaldehyde, ethanol, acetate, and methane .”
