The ethylene glycol it is the simplest organic compound in the glycol family. Its chemical formula is CtwoH6ORtwo, while its structural formula is HOCHtwo-CHtwoOH. A glycol is an alcohol characterized by having two hydroxyl groups (OH) attached to two neighboring carbon atoms in an aliphatic chain.
Ethylene Glycol is a clear, colorless, and odorless liquid. In the image below you have a sample of him in a jar. In addition, it has a sweet taste and is very hygroscopic. It is a low volatile liquid, so it exerts a very small vapor pressure, the vapor density being greater than the air density..
Ethylene glycol is a compound of great solubility in water, in addition to being miscible with many organic compounds; such as short chain aliphatic alcohols, acetone, glycerol, etc. This is due to their ability to donate and accept hydrogen bonds from protic solvents (which have H).
Ethylene glycol polymerizes into numerous compounds, the names of which are often abbreviated to the acronym PEG and a number that indicates their approximate molecular weight. PEG 400, for example, is a relatively small, liquid polymer. While large PEGs are white solids with a greasy appearance.
The property of ethylene glycol to depress the melting point and increase the boiling point of water, allows its use as a coolant and anticoagulant in vehicles, airplanes and computer equipment.
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Ethane-1,2-diol (IUPAC), ethylene glycol, monoethylene glycol (MEG), 1-2-dihydroxyethane.
62.068 g / mol
Clear, colorless and viscous liquid.
Toilet
Candy
1.1132 g / cm3
-12.9 ºC
197.3 ºC
Miscible with water, highly hygroscopic compound.
Miscible with lower aliphatic alcohols (methanol and ethanol), glycerol, acetic acid, acetone and similar ketones, aldehydes, pyridine, coal tar bases, and soluble in ether. Practically insoluble in benzene and its homologues, chlorinated hydrocarbons, petroleum ether and oils.
111 ºC
2.14 in relation to air taken as 1.
0.092 mmHg at 25 ° C (by extrapolation).
When heated to decomposition it emits acrid and irritating smoke.
2-8 ºC
1,189.2 kJ / mol
50.5 kJ / mol
47.99 mN / m at 25 ºC
1.4318 at 20 ºC
pKa = 14.22 at 25 ºC
6 to 7.5 (100 g / L of water) at 20 ºC
Log P = - 1.69
In the upper image we have the ethylene glycol molecule represented by a model of spheres and bars. The black spheres correspond to the carbon atoms, which make up their C-C skeleton, and at their ends we have the red and white spheres for the oxygen and hydrogen atoms, respectively..
It is a symmetric molecule and at first glance it can be thought that it has a permanent dipole moment; however, their C-OH bonds rotate, which favors the dipole. It is also a dynamic molecule, which undergoes constant rotations and vibrations, and is capable of forming or receiving hydrogen bonds thanks to its two OH groups..
In fact, these interactions are responsible for ethylene glycol having such a high boiling point (197 ºC).
When the temperature drops to -13 ºC, the molecules coalesce in an orthorhombic crystal, where rotamers play an important role; that is, there are molecules that have their O-H groups oriented in different directions.
The initial step in the synthesis of ethylene glycol is the oxidation of ethylene to ethylene oxide. In the past, ethylene was reacted with hypochlorous acid to produce chlorohydrin. This was then treated with calcium hydroxide to produce ethylene oxide..
The chlorohydrin method is not very profitable and a method of direct oxidation of ethylene in the presence of air or oxygen was switched to, using silver oxide as a catalyst..
Hydrolysis of ethylene oxide (EO) with water under pressure produces a crude mixture. The water-glycol mixture is evaporated and recycled, separating monoethylene glycol from diethylene glycol and triethylene glycol by fractional distillation..
The ethylene oxide hydrolysis reaction can be outlined as follows:
CtwoH4O + HtwoO => OH-CHtwo-CHtwo-OH (ethylene glycol or monoethylene glycol)
Mitsubishi Chemical developed a catalytic process, through the use of phosphorus, in the conversion of ethylene oxide into monoethylene glycol.
In the Omega process, ethylene oxide is initially converted to ethylene carbonate, through its reaction with carbon dioxide (COtwo). Then, the ethylene carbonate is subjected to a catalytic hydrolysis to obtain the monoethylene glycol with 98% selectivity.
There is a relatively new method for the synthesis of ethylene glycol. This consists of the oxidative carbonylation of methanol to dimethyl oxalate (DMO) and its subsequent hydrogenation to ethylene glycol..
The mixture of ethylene glycol with water allows a decrease in the freezing point and an increase in the boiling point, allowing car engines not to freeze in the winter, nor overheat in the summer.
When the percentage of ethylene glycol in the mixture with water reaches 70%, the freezing point is -55 ºC, so the ethylene glycol-water mixture can be used as a cooling liquid, and protection against freezing in those conditions in which it may occur.
The low freezing temperatures of ethylene glycol solutions allow its use as antifreeze in automobile engines; de-icing of aircraft wings; and in the deicing of the windshields.
It is also used to preserve biological samples preserved at low temperatures, thus avoiding the formation of crystals that can damage the structure of the samples..
The high boiling point allows ethylene glycol solutions to be used to maintain low temperatures in devices or equipment that generate heat when operating, such as: automobiles, computer equipment, air conditioners, etc..
Ethylene glycol is a very hygroscopic compound, which has allowed its use to treat gases extracted from the subsoil that have a high content of water vapors. The elimination of water from natural gases favors their efficient use in their respective industrial processes..
Ethylene glycol is used for the synthesis of polymers, such as polyethylene glycol (PEG), polyethylene terephthalate (PET) and polyurethane. PEGs are a family of polymers used in applications such as: thickening of food, treatment of constipation, cosmetics, etc..
PET is used in the production of all kinds of disposable containers, which are used in different types of beverages and food. Polyurethane is used as a thermal insulator in refrigerators and as a filler in different types of furniture.
It is used in the manufacture of dynamite, allowing that by having a decrease in the freezing point of nitroglycerin, it can be stored with less risk..
Ethylene glycol is used in the treatment of wood to protect it against its rot, produced by the action of fungi. This is important for the preservation of museum art works.
Ethylene glycol is present in media for suspending conductive salts in electrolytic capacitors and in soy foam stabilizers. It is also used in the manufacture of plasticizers, elastomers and synthetic waxes.
Ethylene glycol is used in the separation of aromatic and paraffinic hydrocarbons. In addition, it is used in the manufacture of detergents for cleaning equipment. Increases viscosity and decreases volatility of the ink, making it easier to use.
Also, ethylene glycol can be used in the foundry of molding sand and as a lubricant during the grinding of glass and cement. It is also used as an ingredient in hydraulic braking fluids and as an intermediate in the synthesis of esters, ethers, polyester fibers and resins..
Among the resins in which ethylene glycol is used as a raw material is the alkyd, used as the base of alkyd paints, applied in automotive and architectural paints..
Ethylene glycol has low acute toxicity when it acts by contact on the skin or if it is inhaled. But, its toxicity is fully manifested when ingested, being indicated as the fatal dose of ethylene glycol of 1.5 g / kg of body weight, or 100 mL for a 70 kg adult..
Acute exposure to ethylene glycol produces the following symptoms: inhalation causes cough, dizziness and headache. On the skin, by contact with ethylene glycol, dryness occurs. Meanwhile, in the eyes it produces redness and pain.
Ingestion of ethylene glycol is manifested by abdominal pain, nausea, unconsciousness, and vomiting. An excessive intake of ethylene glycol has a damaging effect on the central nervous system (CNS), cardiovascular function and kidney morphology and physiology..
Due to failures in the functioning of the CNS, paralysis or irregular eye movement (nystagmus) occurs. In the cardiopulmonary system, there is high blood pressure, tachycardia, and possible heart failure. There are serious alterations in the kidney, product of intoxication with ethylene glycol.
Dilation, degeneration, and calcium oxalate deposition occur in the renal tubules. The latter is explained by the following mechanism: ethylene glycol is metabolized by the lactic dehydrogenase enzyme to produce glycoaldehyde.
Glycoaldehyde gives rise to glycolic, glyoxylic, and oxalic acids. Oxalic acid precipitates rapidly with calcium to form calcium oxalate, the insoluble crystals of which are deposited in the renal tubules, producing morphological alterations and dysfunction in them, which can lead to kidney failure..
Due to the toxicity of ethylene glycol it has been gradually replaced, in some of its applications, by propylene glycol.
During their de-icing, airplanes release significant amounts of ethylene glycol, which end up accumulated on the landing strips, which, when washed, causes the water to transfer ethylene glycol, through the drainage system, to rivers where its toxicity affects the life of the aircraft. fish.
But it is not the toxicity of ethylene glycol itself that is the main cause of ecological damage. During its aerobic biodegradation, a significant amount of oxygen is consumed, causing its decrease in surface waters.
On the other hand, its anaerobic biodegradation can release toxic substances for fish, such as acetaldehyde, ethanol, acetate and methane..
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