ETHYLENE GLYCOL: PROPERTIES, CHEMICAL STRUCTURE, USES - CHEMISTRY - 2025

The ethylene glycol is the simplest organic compound of the family of glycols. Its chemical formula is C ₂ H ₆ O ₂, while its structural formula is HOCH ₂ -CH ₂ OH. 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, which is why it exerts a very small vapor pressure, the density of the vapor being greater than the density of air.

Bottle with ethylene glycol in its content. Source: Σ64

Ethylene glycol is a compound with 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 many compounds, the names of which are often abbreviated to PEG and a number that indicates their approximate molecular weight. PEG 400, for example, is a relatively small, liquid polymer. Meanwhile, large PEGs are white solids with a greasy appearance.

Ethylene glycol's property of depressing the melting point and increasing the boiling point of water allows it to be used as a coolant and anticoagulant in vehicles, aircraft, and computer equipment.

Properties

Names

Ethane-1,2-diol (IUPAC), ethylene glycol, monoethylene glycol (MEG), 1-2-dihydroxyethane.

Molar mass

62.068 g / mol

Physical appearance

Clear, colorless and viscous liquid.

Odor

Toilet

Taste

Sweet

Density

1.1132 g / cm ³

Melting point

-12.9 ºC

Boiling point

197.3 ºC

Water solubility

Miscible with water, very hygroscopic compound.

Solubility in other solvents

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.

ignition point

111 ºC

Vapor density

2.14 in relation to air taken as 1.

Vapor pressure

0.092 mmHg at 25 ° C (by extrapolation).

Decomposition

When heated to decomposition, it emits acrid and irritating smoke.

Storage temperature

2-8 ºC

Heat of combustion

1,189.2 kJ / mol

Heat of vaporization

50.5 kJ / mol

Surface tension

47.99 mN / m at 25 ° C

Refractive index

1.4318 at 20 ºC

Dissociation constant

pKa = 14.22 at 25 ºC

pH

6 to 7.5 (100 g / L of water) at 20 ºC

Octanol / water partition coefficient

Log P = - 1.69

Chemical structure

Molecular structure of ethylene glycol. Source: Ben Mills via Wikipedia.

In the upper image we have the ethylene glycol molecule represented by a spheres and bars model. The black spheres correspond to the carbon atoms, which make up its CC 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 ° C, the molecules coalesce in an orthorhombic crystal, where rotamers play an important role; that is, there are molecules that have their OH groups oriented in different directions.

Production

Ethylene oxidation

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, using silver oxide as a catalyst.

Ethylene oxide hydrolysis

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 hydrolysis reaction of ethylene oxide can be outlined as follows:

C ₂ H ₄ O + H ₂ O => OH-CH ₂ -CH ₂ -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.

Omega process

In the Omega process, ethylene oxide is initially converted to ethylene carbonate, through its reaction with carbon dioxide (CO ₂). Then, the ethylene carbonate is subjected to catalytic hydrolysis to obtain 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.

Applications

Coolant and antifreeze

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 as protection against freezing in those conditions in which it may occur.

The low freezing temperatures of ethylene glycol solutions allow its use as antifreeze for automobile engines; de-icing of aircraft wings; and in the deicing of the windshields.

It is also used to preserve biological samples kept 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.

Dehydration

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.

Polymer manufacturing

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 foods, 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.

Explosives

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.

Wood protection

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 works of art in museums.

Other apps

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. It increases the viscosity and reduces the volatility of the ink, which makes 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 alkyd, used as the base of alkyd paints, applied in automotive and architectural paints.

Poisoning and risks

Symptoms from exposure

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 coughing, dizziness and headache. On the skin, by contact with ethylene glycol, dryness occurs. Meanwhile, in the eyes it produces redness and pain.

Ingestion damage

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, hypertension, tachycardia, and possible heart failure occur. There are serious alterations in the kidney, product of the poisoning 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 cause renal failure.

Due to the toxicity of ethylene glycol it has been gradually replaced, in some of its applications, by propylene glycol.

Ecological consequences of ethylene glycol

During their de-icing, airplanes release significant amounts of ethylene glycol, which end up accumulating 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 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 substances toxic to fish, such as acetaldehyde, ethanol, acetate and methane.

References

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