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Ethylene Glycol

What is ethylene glycol?

Ethylene glycol or ethane-1,2-diol is a colourless viscous liquid with the formula (CH2OH)2. It is missable in all proportions with water and alcohol but insoluble in ether. The prefix glyc in ethylene glycol indicates that the organic compound has a sweet taste. It is widely used as a solvent and antifreezing agent. In chemistry, the high viscosity, boiling point, and solubility of ethylene glycol due to the hydrogen bonding of all hydroxyl groups.

Ethylene glycol properties

It is a highly poisonous dihydric alcohol containing two hydroxyl groups. The chemical properties and reactions of ethylene glycol are similar to those of primary alcohol. One hydroxyl group is always completely attacked before the other reacts. Some properties ethane-1,2-diol are given below the table,

Ethylene glycol properties
Chemical formula C2H6O2
IUPAC name ethane-1,2-diol
Molar mass 62.068 g/mol
Appearance colourless viscous liquid
Density 1.1132 g/cm3
Melting point −12.9 °C
Boiling point 197.3 °C
Viscosity 1.61×10−2 Pa-s

Production process

It is the simplest glycol may be prepared by following methods given below the picture,

Ethylene Glycol Properties and preparation from ethylene, ethylene oxide and ethylene dibromide

Ethylene oxide to ethylene glycol

Industrially, it is produced by treating ethylene oxide with dilute hydrochloric acid. In presence of concentrated halogen acids, ethane-1,2-diol is converted into ethylene halohydrins.

Ethylene to ethylene glycol

It is prepared by passing ethylene into a cold dilutes alkaline permanganate solution. Ethylene is also converted into chlorohydrin when passing hypochlorous acid. Hydrolyzing ethylene chlorohydrin by boiling with aqueous sodium hydrogen carbonate produced ethane-1,2-diol. It can be prepared from ethylene dibromide by boiling with aqueous sodium carbonate.

Reactions of ethylene glycol

In ethylene glycol, one hydroxyl group readily reacts before another. Therefore, sodium at 50 °C forms the monosodium salt. The di-sodium salt is obtained only when the temperature is raised to 160 °C. It reacts with hydrogen chloride to form chlorohydrin at 160 °C. Whereas at 200 °C, ethane-1,2-diol produced ethylene dichloride. Some important chemical reactions are given below the picture,

Reactions of ethylene glycol to form ethylene dibromide, diacetate, 1,3-dioxolane and acetaldehyde

  • Ethylene dihalide is obtained when ethane-1,2-diol is treated with phosphorus trichloride or phosphorus tribromide.
  • Di-ester is obtained when ethane-1,2-diol is treated with organic acids or inorganic oxo-acids. The obtained product is depending upon the relative amounts of glycol and acid. For example, glycol diacetate is obtained when glycol heating with acetic acid in presence of a small amount of sulfuric acid.
  • It condensed with aldehydes or ketones in presence of p-toluene sulphonic acid to formed respective cyclic acetals or cyclic ketals.
  • It is converted into aldehyde when heated with dehydrating agents like zinc chloride (ZnCl2).

Oxidation reactions

It is oxidized with nitric acid to obtained glycolic acid and oxalic acid. Oxidation of glycols with acid, alkaline or neutral permanganate, acid dichromate, chromic acid or lead tetra-acetate, or periodic acid gives aldehyde, acids, or ketones by fusion of C-C chemical bond. Oxidation of cis-glycol occurs more rapidly than the corresponding trans-glycol due to the formation of a cyclic intermediate. These oxidations are also influenced by strict hindrance. It is oxidized much faster than pinacol by periodic acid.

Uses of ethylene glycol

  • lt is used as a coolant and antifreezing agent in industry and cars. It helps to freeze our car in the winter season and coolant to reduce overheating in the summer season.
  • For the production of polyester, we used a large quantity of ethylene glycol as raw materials. This polyester is used for making different types of clothes, carpets, pillows, fiberglass, etc.
  • In a geothermal pump, it is used as a fluid that transports heat through it.
  • Due to low specific heat capacity, it is mixed with water to decrease the boiling point of water. The mixture is used as a coolant solution in many antifreezing systems.
  • When ethane-1,2-diol is heated with a dehydrating agent like phosphoric acid, it produced polyethylene glycols. These condensed polymers contain both alcohol and ether functional groups. They are soluble in water and used as solvents. They are widely used as solvents for gums, resins, cellulose ester, etc.
  • A small amount of ethylene glycol is used for the manufacture of capacitors and 1,4-dioxane.