Difference Between Ethylene Glycol and Propylene Glycol

Main Difference – Ethylene Glycol vs Propylene Glycol

Both ethylene glycol and propylene glycol are alcoholic compounds which have two –OH groups per molecule. Ethylene glycol has two carbon atoms, and propylene glycol has three carbon atoms per molecule. These organic compounds have important applications depending on the chemical structure of the compound. The main difference between ethylene glycol and propylene glycol is that ethylene glycol is toxic whereas propylene glycol is moderately toxic.

Key Areas Covered

1. What is Ethylene Glycol
      – Definition, Properties, Uses
2. What is Propylene Glycol
      – Definition, Applications
3. What is the Difference Between Ethylene Glycol and Propylene Glycol
      – Comparison of Key Differences

Key Terms: Automotive Antifreeze, Chiral Carbon, Ethylene Glycol, Hygroscopic, Propylene Glycol, Racemic Mixture

What is Ethylene Glycol

Ethylene glycol is a syrupy alcoholic liquid compound having the chemical formula C₂H₆O₂. The molar mass of this compound is about 62.07 g/mol. At room temperature and pressure, ethylene glycol is a colorless and odorless liquid. It is a viscous liquid. The boiling point of this liquid is about 198 °C.

Figure 1: 3D Ball and Stick Model for Ethylene Glycol

Ethylene glycol is a toxic compound. Even a small amount of this liquid can be harmful. Ingestion of this liquid can lead to shock or even death. However, it is very useful as a chemical and can be found in many household items such as detergents, cosmetics, etc.

The most common applications of ethylene glycol include its use as raw material for the production of polyester fibers and as an automotive antifreeze. An automotive antifreeze is a liquid which is used in radiators and cooling systems of internal combustion engines in vehicles. However, it is a moderately toxic compound.

What is Propylene Glycol

Propylene Glycol is a synthetic organic compound that has the chemical formula C₃H₈O₂. The IUPAC name for this compound is Propane-1,2-diol. This indicates that propylene glycol has two –OH groups. Therefore, it is an alcoholic compound. The molar mass of propylene glycol is about 76.1 g/mol. At room temperature, it is a clear liquid.

Propylene glycol is hygroscopic. This means it absorbs water when exposed to the atmosphere. Since there is a chiral carbon (asymmetric carbon) in propylene glycol molecule, the synthesized product is always a racemic mixture of two enantiomers. However, advanced methods can be used to obtain pure isomer out of the racemic mixture.

Figure 2:  3D Ball and Stick Model for Propylene Glycol

Propylene glycol is used as a solvent for intravenous, oral, and topical pharmaceutical preparations. It is generally considered safe. But large amounts can be toxic. Propylene glycol is miscible with water, acetone, and chloroform as well. Propylene glycol is also used to make polyester compounds and as a base for de-icing solutions.

Difference Between Ethylene Glycol and Propylene Glycol

Definition

Ethylene Glycol: Ethylene glycol is a syrupy alcoholic liquid compound having the chemical formula C₂H₆O₂.

Propylene Glycol: Propylene Glycol is a synthetic organic compound that has the chemical formula C₃H₈O₂.

Toxicity

Ethylene Glycol: Ethylene glycol is toxic.

Propylene Glycol: Propylene glycol is moderately toxic.

IUPAC Name

Ethylene Glycol: IUPAC name for Ethylene glycol is Ethane-1,2-diol.

Propylene Glycol: IUPAC name for Propylene glycol is Propane-1,2-diol.

Molar Mass

Ethylene Glycol: The molar mass of Ethylene glycol is about 62.07 g/mol.

Propylene Glycol: The molar mass of Propylene glycol is about 76.10 g/mol.

Applications

Ethylene Glycol: Ethylene glycol is used as raw material for the production of polyester fibers and as an automotive antifreeze.

Propylene Glycol: Propylene Glycol is used as a solvent for intravenous, oral, and topical pharmaceutical preparations.

Conclusion

Ethylene glycol and propylene glycol are organic compounds. They are alcoholic compounds due to the presence of –OH groups. The main difference between ethylene glycol and propylene glycol is that ethylene glycol is toxic whereas propylene glycol is moderately toxic.

References:

 1. “1,2-Propanediol.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
2. “Propylene glycol.” Wikipedia, Wikimedia Foundation, 6 Nov. 2017, Available here.
3. “ETHYLENE GLYCOL.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.

Image Courtesy:

1. “Ethylene-glycol-3D-balls” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
2. “PropyleneGlycol-stickAndBall” By Karlhahn – Own work (Public Domain) via Commons Wikimedia