Glycerol

OVERVIEW

Glycerol (GLIH-ser-ol) is a clear, colorless, odorless, sweet-tasting syrupy liquid. It is a trihydric alcohol, meaning that its molecules contain three hydroxyl (?OH) groups. Glycerol occurs naturally in all animal and plant cells. Glycerol was discovered in 1779 by the German chemist Karl Wilhelm Scheele (1742–1786) and named by the French chemist Michel Eugéne Chevreul (1786–1889) because of its sweet taste (glycos means "sweet" in Greek). In 1836 the French chemist Théophile-Jules Pelouze (1807–1867) determined the molecular formula for glycerol, and three decades later, in 1872, the compound was first synthesized (created in a laboratory) by the French chemist Charles Friedel (1832–1899). About 250 million kilograms (500 million pounds) of glycerol are produced in the United States each year, the majority of which goes to the production of food and personal care products.

KEY FACTS

OTHER NAMES:

Glycerin; glycerine; glycyl alcohol

FORMULA:

CH₂OHCHOHCH₂OH

ELEMENTS:

Carbon, hydrogen, oxygen

COMPOUND TYPE:

Trihydric alcohol (organic)

STATE:

Liquid

MOLECULAR WEIGHT:

92.09 g/mol

MELTING POINT:

18.1°C (64.6°F)

BOILING POINT:

290°C (554°F)

SOLUBILITY:

Miscible with water and alcohol; insoluble in ether, benzene, and chloroform

HOW IT IS MADE

The traditional method of making glycerol is by the saponification of fats. Fats are the esters of glycerol and one or more alcohols. When a fat is hydrolyzed in the presence of a catalyst, it is converted into the glycerol and alcohols from which it was originally made. This type of hydrolysis is called saponification because it is the usual method by which soaps (the Latin word for "soap" is sapon). Glycerol can be obtained, then, as a byproduct in the manufacture of soaps.

A number of synthetic methods for making glycerol are also available. Most of these procedures begin with propylene (propene; CH₂=CHCH₃) and chlorine and involve a series of steps that convert the three-carbon propylene to the three-carbon glycerol. Glycerol can also be obtained by treating simple sugars with hydrogen over a nickel catalyst. In the United States, about 80 percent of all glycerol produced is obtained by saponification methods, and the remaining 20 percent is made by synthetic methods.

COMMON USES AND POTENTIAL HAZARDS

The most common use for glycerol in the United States is in food products, where it acts as a sweetener and as a thickener in many foods. For example, it is added to ice cream to improve texture and to candy products and baked goods to increase the sweetness of the product. It is also used to make the flexible coatings on cheeses, sausages, and other meat products. About one-quarter of all glycerol made in the United States is used in the food products industry.

Nearly the same amount of glycerol is used in the preparation of personal care products, such as skin, hair, and soap products (23 percent) and in oral hygiene products, such as toothpastes and mouthwashes (17 percent). Some of the products that include glycerol are moisturizers, detergents, soaps, hair coloring agents, mascara, nail polish, nail polish removers, perfumes, body lotions, hair sprays, shaving creams, lipsticks, cough medicines, shampoos, and hair conditioners. Glycerol is also used as a humectant in tobaccos. A humectant is a material that helps a product conserve moisture and prevent it from drying out.

Interesting Facts

• As winter approaches, many insects begin to produce glycerol to replace the water in their body tissues. Glycerol acts as an antifreeze to prevent the insects from freezing during the coldest part of the year.

Other uses for glycerol include:

• In the manufacturer of explosives;
• In the production of a variety of plastics and polymers, such as polyether polyols, urethanes, and alkyd resins;
• As a lubricant in pumps, bearings, gaskets, and other mechanical systems;
• In the manufacture of ink rolls, inks, and rubber stamps;
• As an emulsifying agent, a material that helps two liquids that are not soluble in each other to stay mixed;
• As an antifreeze; and
• In a number of medical applications, such as the treatment of glaucoma and stroke.

Glycerol poses some safety problems because it is combustible and explosive under certain conditions. It presents no health hazards under normal circumstances of use, however.

Words to Know

ESTER

An organic compound formed in the reaction between an organic acid and an alcohol.

HYDROLYSIS

The process by which a compound reacts with water to form two new compounds.

MISCIBLE

able to be mixed; especially applies to the mixing of one liquid with another.

SYNTHESIS

A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.

FOR FURTHER INFORMATION

"Glycerol." International Chemical Safety Cards. http://www.healthy-communications.com/msdsglycerin1.html (accessed on October 10, 2005).

"Glycerol." PDRhealth. http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/gly_0304.shtml (accessed on October 10, 2005).

Legwold, Gary. "Hydration Breakthrough." Bicycling (July 1994): 72-73.

"Material Safety Data Sheet: Glycerine." Department of Chemistry, Iowa State University. http://avogadro.chem.iastate.edu/MSDS/glycerine.htm (accessed on October 10, 2005).