Ethylene glycol

Ethylene glycol (monoethylene glycol (MEG), antifreeze. In its pure form, it is an odorless, colorless, syrupy liquid with a sweet taste. Ethylene glycol is toxic, and its accidental ingestion should be considered a medical emergency.

Production

Ethylene glycol is produced from ethylene, via the intermediate chemical equation

C₂H₄O + H₂O → HOCH₂CH₂OH

This reaction can be tetraethylene glycol.

This molecule has been observed in space by Hollis, et al.^[2]

Uses

Coolant

The major use of ethylene glycol is as a coolant or antifreeze in, for example, automobiles and personal computers. Due to its low freezing point, it is also used as a deicing fluid for windshields and aircraft. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water.

Manufacturing

Ethylene glycol has become increasingly important in the vitrification mixtures for low-temperature preservation of biological tissues and organs.

Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of corrosion in liquid cooling systems for personal computers.

Chemistry

Ethylene glycol may also be used as a azeotropic distillation to shift the equilibrium to the right.^[4]

Laboratory use

Ethylene glycol is commonly used in laboratories to precipitate out proteins in solution. This is often an intermediary step in fractionation, purification and/or crystallization. It can be used to protect functional groups from reacting during organic synthesis. To get the functional group back to its original composition, simply add water and acid.

Ethylene glycol is commonly used as a preservative for specimens in schools, frequently during dissection. It is said to be safer than formaldehyde, but the safety is questionable.

Other applications

Ethylene glycol's high boiling point and affinity for water makes it an ideal hydrocarbon gases from the bottom. The glycol chemically removes the water vapor, allowing dry gas to exit from the top of the tower. The glycol and water are separated, and the glycol cycles back through the tower.

Instead of removing water Ethylene glycol can also be used to depress the temperature at which hydrates are formed. The purity of glycol used for hydrate suppression (mono-ethylene glycol) is typically around 80%, whereas the purity of glycol used for dehydration (tri-ethylene glycol) is typically 95-99+%. Moreover, the injection rate for hydrate suppression is much lower than the circulation rate in a glycol dehydration tower.

Ethylene glycol is also used in the manufacture of some vaccines, but it is not itself present in these injections. It is used as a minor (1–2%) ingredient in shoe polish and also in some inks and dyes. Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after the fact. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats, and is relatively cheap.

Toxicity

The major danger from ethylene glycol is following ingestion. Due to its sweet taste, children and animals will sometimes consume large quantities of it if given access to antifreeze. Ethylene glycol may also be found as a contaminant in Ethanol acts as a competitive inhibitor to the active site of the enzyme that converts ethylene glycol to its toxic metabolites. Once ethanol binds, the ethylene glycol is harmlessly excreted out of the body.

Ethylene glycol poisoning is a medical emergency and in all cases a poison control center should be contacted or medical attention should be sought. It is highly toxic with an estimated LD₁₀₀ in humans of approximately 1.4 ml/kg.^[5] However, as little as 30 milliliters (2 tablespoons) can be lethal to adults.^[6]

Symptoms

Symptoms of ethylene glycol poisoning usually follow a three-step progression, although poisoned individuals will not always develop each stage or follow a specific time frame.^[5] Stage 1 consists of neurological symptoms including victims appearing to be intoxicated, exhibiting symptoms such as dizziness, headaches, slurred speech, and confusion. Over time, the body calcium oxalate crystals in the kidney.

Treatment

Initial treatment consists of stabilizing the patient and gastric decontamination. As ethylene glycol is rapidly absorbed, gastric decontamination needs to be performed soon after ingestion to be of benefit. Gastric lavage or nasogastric aspiration of gastric contents are the most common methods employed in ethylene glycol poisoning. activated charcoal (charcoal does not adsorb glycols) are not recommended. ^[5]

The alcohol dehydrogenase, thus blocking the formation of the toxic metabolites.^[8]

In addition to antidotes, hemodialysis can also be used to enhance the removal of unmetabolized ethylene glycol, as well as its metabolites from the body. Hemodialysis also has the added benefit of correcting other metabolic derangements or supporting deteriorating kidney function caused by ethylene glycol ingestion. Often both antidotal treatment and hemodialysis are used together in the treatment of poisoning.

Industrial hazards

Ethylene glycol can begin to breakdown at 230° – 250°F (110° – 121°C). Note that breakdown can occur when the system bulk (average) temperature is below these limits because surface temperatures in heat exchangers and boilers can be locally well above these temperatures.

The exothermic reaction. The Apollo 1 fire catastrophe was caused by this reaction. The ethylene glycol–water mixture was ignited and was able to burn in the atmosphere of pure low pressure oxygen.^{[citation needed]}

History

Ethylene glycol was first prepared in 1859 by the French chemist ethylene oxide, a component in its synthesis, became cheaply available.

When first introduced it created a minor revolution in aircraft design because when used in place of water as an engine coolant, its higher evaporative cooling systems which used water at high pressure. Invariably, these proved to be rather unreliable and were easily damaged in combat because they took up large amounts of room on the plane, where they were easily hit by gunfire.

References