Ethylene glycol is an organic compound. It is highly toxic and is also called Ethane-1,2-diol or Monoethylene glycol. It is odourless and is viscous. Ethylene glycol is colourless and has a sweet taste. It appears as a clear, colourless, liquid. Ethylene glycol is broadly in use as an antifreeze and a raw material in the plastic industry. It is made when ethylene oxide reacts with water.
Introduction to Ethylene Glycol
Ethylene glycol is the most abundantly produced diol. It is one of the monomers of polyethylene terephthalate. Ethylene glycol has been synthesized by the oxidation of ethylene with \(O_2\) to ethylene oxide and the hydration of ethylene oxide to ethylene glycol.
The molecular weight or molar mass of ethylene glycol is 62.07 gram per mole. The density of ethylene glycol is 1.11 gram per centimetre cube. The boiling point of ethylene glycol is \(197.3^oC\). The melting point of ethylene glycol is \(-12.9^oC\).
Production of Ethylene Glycol
- Ethylene glycol is produced with the help of ethylene (ethene), through the intermediate ethylene oxide. Ethylene oxide reacts with water to give ethylene glycol according to the chemical equation:
\(C_2H_4O + H_2O \rightarrow HO−CH_2CH_2−OH\)
This reaction can be catalysed by either acids or bases. It can also occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol are at acidic or neutral pH with excess water. Under these conditions, ethylene glycol yields up to 90%. The major by-products produced are the oligomers diethylene glycol, triethylene glycol, and tetraethylene glycol. The separation of these oligomers and water is an energy-intensive process. About 6.7 million tonnes are produced annually.
- Ethylene glycol can be produced by hydrolysis of ethylene oxide. Ethylene oxide obtained after catalytic oxidation of ethylene is hydrolysed in the presence of dilute acid or base at high temperature to ethylene glycol.
- Oxalic esters on reduction with sodium and alcohol give ethylene glycol.
The Chemical Reaction of Ethylene Glycol
Ethylene glycol is in use as a protecting group for carbonyl groups. Treating a ketone or aldehyde with ethylene glycol in the presence of an acid catalyst gives 1,3-dioxolane. This is resistant to bases and other nucleophiles. The 1,3-dioxolane protecting group is thereafter removed by further acid hydrolysis processes. For example, isophorone is protected with the help of ethylene glycol with p-toluenesulfonic acid. Water is removed by an azeotropic distillation process to shift the equilibrium to the right.
Toxicity of Ethylene Glycol
Ethylene glycol is moderately toxic for humans. The major danger is because of its sweet taste, which attracts children and animals. Ethylene glycol upon ingestion is oxidized to glycolic acid. This, in turn, oxidizes to oxalic acid, which is toxic. It and its toxic byproducts first affect the central nervous system of the body, then the heart, and finally the kidneys. Ingestion of sufficient amounts of ethylene glycol is fatal if untreated. Several deaths are recorded annually in the U.S. alone because of ethylene glycol.
Uses of Ethylene Glycol \(C_2H_6O_2)\)
It is useful in the following manner:
- Manufacture of polyester as a raw agent
- Antifreeze formulation
- In Air conditioning systems
- As a precursor in the plastic industry
- In convective heat transfer
- As a dehydrating agent in the gas industry
- As a desiccant
- In use as an additive
- In the manufacturing of capacitor
- To preserve biological specimens
- As an ingredient in shoe polish
- In the manufacturing of some vaccines
FAQs on Ethylene Glycol
Question 1: Is ethylene glycol alcohol?
Answer: Ethylene glycol or ethane-1,2-diol, is a member of the organic compound family glycol. Glycol is alcohol on the nearby carbon atoms, with two hydroxyl groups. The common name ethylene glycol means “ethylene derived glycol.”
Question 2: Is ethylene glycol corrosive?
Answer: Ethylene glycol is corrosive. Most corrosion from ethylene glycol is due to decomposition at higher temperatures of organic acids such as glycolic acid.
Question 3: Is ethylene glycol polar?
Answer: Ethylene glycol comprises polar O-H groups. These groups are polar since oxygen is much more electronegative than hydrogen, and therefore appears to polarize the pair of electrons in the O-H bond.