Have you ever wondered what chemical compounds make up soap and other personal care products? If we look at the product labels on some of them, one of the ingredients is a compound called glycerol. In this lesson we will learn more about glycerol.

What is Glycerol?

Let’s think about some products we always use, like soap or shaving cream. Have you ever wondered what component of soap makes it slippery? For the shaving cream, what ingredient in it is responsible for softening your skin? The answer is that both these products have a chemical compound called glycerol.

Glycerol, also referred to as glycerin or glycerine, is a chemical compound that is a generally nontoxic, sweet-tasting viscous liquid. When we say viscous, this term means that the substance is a liquid with a thick and sticky consistency. The formula for glycerol is C3H8O3. It has 3 carbon (C) atoms, 8 hydrogen (H) atoms, and 3 oxygen (O) atoms. In this image, you can see the appearance of glycerol and its chemical formula and structure.

The chemical structure of glycerol shows that each carbon atom is bonded to an -OH group. These -OH groups are what we call hydroxyl groups. Because of this, glycerol is classified as a polyol, which is an alcohol containing more than one hydroxyl group. Glycerol is soluble in water because of the hydroxyl (-OH) groups attached to the carbon atoms. These hydroxyl groups are also responsible for the hygroscopic nature of glycerol, which means that it readily retains or takes up water.

The density of glycerol is 1.261 g/ml. Its boiling point is 290 degrees Celsius, and its melting point is 17.8 degrees Celsius. These values show that glycerol is denser than water (because water has a density of 1 g/mL), its boiling point is higher than water (water has a boiling point of 100 degrees Celsius), and its melting point is higher than water (water has a melting point of 0 degrees Celsius).

Uses

Glycerol is mostly known for its use in the food industry as well as in personal care products. It is also used as antifreeze and even as one of the ingredients to manufacture explosives. In this section, we will discuss the various uses of glycerol.

Personal Care Products

Have you ever wondered what it is that makes your toothpaste smooth? It would really not be a very good experience if your toothpaste felt rough! Earlier, we mentioned that glycerol is the ingredient that makes soap slippery, and the ingredient that helps soften your skin when you put shaving cream on. Glycerol is widely used in various personal care products as a smoothing agent, so it’s responsible for making your toothpaste smooth.

You may wonder how it is that when you use soap, your skin is still soft and smooth to the touch, not dry and flaky. This is most definitely because of glycerol! It’s used in many skin care and hair care products because it serves as a lubricant. Some of us may have used products with herbal extracts. When extracting fluid from a plant or herb, glycerol is used as the solvent to extract enzymes from plants. These herbal extracts are then added to some personal care products.

Pharmaceutical Products

Glycerol is a very widely used component in various pharmaceutical products like capsules, syrups, topical creams, and suppositories. We mentioned earlier that glycerol is sweet tasting. Have you ever taken cough syrup or lozenges that tasted sweet? This is all thanks to glycerol.

Do you also notice how there are tablets or capsules that have a smooth coating? This helps tremendously in making sure they go down smoothly. Have you noticed the nice, smooth consistency of topical creams that go on your skin? This consistency is also because of the addition of glycerol. In drug powders, glycerol is also used as a levigating agent, which helps reduce the particle size when grinding. This helps the powders to be mixed thoroughly and evenly with other ingredients.

Food Industry

Glycerol is a common food and drink additive because it is nontoxic and has a sweet tasting flavor. In some liqueurs, since glycerol is viscous, it serves as a thickening agent. It’s also used a sugar substitute. Do you ever wonder how icing on cake does not get hard? This is because glycerol prevents it from setting too hard.

Don’t you just hate it sometimes when food dries out? Since glycerol is hygroscopic, it can act as a humectant (a substance that retains moisture). So, in baked goods, to keep them from drying out, glycerol is a common additive.

Antifreeze and Explosives

How do we prevent our car engines from freezing in the winter and overheating in the summer? The answer to this is antifreeze, which is an additive that lowers the freezing point of water. Glycerol is used in antifreeze because the hydroxyl groups (-OH) in glycerol bond with the water molecules, resulting in a lower freezing point. Glycerol is also used as one of the starting materials to make the explosive nitroglycerin, which is commonly used in some rocket propellants and dynamites. To make nitroglycerin, glycerol reacts with sulfuric acid and nitric acid.

Lesson Summary

Let’s review. Glycerol is a nontoxic, sweet tasting, and viscous fluid that has the chemical formula C3H8O3. It is a polyol, a compound that is made up of more than one hydroxyl group. Its chemical structure consists of three hydroxyl groups, which are -OH groups attached to the carbon atoms. The presence of these hydroxyl groups makes glycerol soluble in water, as well as hygroscopic, so that it retains water from the surroundings.

Glycerol has many uses in personal care products, pharmaceutical products, and the food industry. Its properties help soften the hair and skin and keep them from drying out. It gives a smooth consistency to tablets and a sweet taste to medicine. In drug powders, glycerol is used as a levigating agent so that the drug particles will be smaller and mix more evenly. It is used as an additive to liqueurs, making them sweet and viscous. In pastries like icing and cookies, it serves as a humectant, a substance that retains moisture, so it keeps them soft. Glycerol is also used in antifreeze because it lowers the freezing point of water. It is also one of the starting materials used to make explosives.

Glycerol Notes

Container of glycerol and description
  • Glycerol is a polyol composed of three hydroxl groups
  • Glycerol is nontoxic, has a sweet taste, and is viscous
  • Because of its properties, glycerol is used in personal care products, pharmaceuticals, and the food industry

Learning Outcomes

After you’ve finished this lesson, you should be able to:

  • State the chemical composition of glycerol
  • Recall the properties glycerol lends to products
  • List the uses for glycerol for different industries