The key difference between propylene glycol and glycerin is that propylene glycol compound has two hydroxyl groups per molecule, whereas glycerin has three hydroxyl groups per molecule.
Propylene glycol and glycerin often look the same since they occur as colourless, odourless, sweet, and syrupy products. Even though they share some physical properties, they have very distinctive features. However, propylene glycol is toxic, and it is very important to identify these two compounds accurately before use.
CONTENTS
1. Overview and Key Difference
2. What is Propylene Glycol
3. What is Glycerin
4. Propylene Glycol vs Glycerin in Tabular Form
5. Summary – Propylene Glycol vs Glycerin
What is Propylene Glycol?
Propylene glycol is a viscous and colourless liquid that is almost odourless and has a faintly sweet taste. It has the chemical formula C3H8O2. There are two alcohol groups in propylene glycol molecules. There are three carbon atoms in a chain and two alcohol groups attached to two of these carbon atoms. Therefore, we can categorize it as a diol. Furthermore, propylene glycol is miscible with many solvents such as water, acetone, and chloroform.
Propylene glycol can be produced on a large scale, mainly for the production of polymers. On an industrial scale, this substance is produced mainly using propylene oxide. This substance has uses in the food industry, pharmaceutical production, and cosmetic production. It is useful as a solvent for both natural and synthetic substances, as a humectant, as a freezing point depressant, as a carrier or base in cosmetic production, for trapping and preserving insects, etc.
What is Glycerin?
Glycerin or glycerol is a simple polyol compound having the chemical formula CHCH2CH2(OH)3. This compound is colorless, odorless, and occurs as a viscous liquid that has a sweet taste and it is also non-toxic. The backbone of this compound is made up of lipids named glycerides.
Glycerin has antimicrobial and antiviral properties. Therefore, it is widely used as an FDA-approved wound and burn treatment. Besides, it is useful as a bacterial culture medium and as an effective marker to measure liver disease. Apart from that, glycerin is commonly used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Since it has three hydroxyl groups, it is miscible with water and also has a hygroscopic nature.
We can get glycerin from plant and animal sources in which it occurs as triglycerides, esters of glycerol along with long-chain carboxylic acids, etc. There are hydrolysis, saponification, or transesterification processes that can be used to make the glycerol and fatty acid derivative triglyceride.
What is the Difference Between Propylene Glycol and Glycerin?
Propylene glycol and glycerin are important organic compounds. They have closely similar structures and properties. The key difference between propylene glycol and glycerin is that the propylene glycol compound has two hydroxyl groups per molecule, whereas glycerin has three hydroxyl groups per molecule. More importantly, propylene glycol is toxic, whereas glycerin is not toxic. Propylene glycol is used to absorb extra water and maintain moisture in certain medicines, cosmetics, and food products, while glycerin is used as a sweetener in the food industry, as a bacterial culture medium, used as an FDA-approved wound and burn treatment, etc.
The below infographic presents the differences between propylene glycol and glycerin in tabular form for side-by-side comparison.
Summary – Propylene Glycol vs Glycerin
Propylene glycol is an organic compound having the chemical formula C3H8O2, while glycerol is a simple polyol compound having the chemical formula CHCH2CH2(OH)3. The key difference between propylene glycol and glycerin is that the propylene glycol compound has two hydroxyl groups per molecule, whereas glycerin has three hydroxyl groups per molecule.
Reference:
1. “Propylene Glycol.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.
2. Ajiboye, Tolu. “Find out What the Uses of Propylene Glycol Are.” Verywell Health.
Image Courtesy:
1. “Glycerin Skelett” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Sample of Glycerine” By LHcheM – Own work (CC BY-SA 3.0) via Commons Wikimedia