Two centuries ago in 1779, Carl W. Scheele, a Swedish chemist, was overjoyed when he discovered a new transparent, syrupy liquid by heating olive oil and litharge. Little did he know that this new chemical substance would soon become indispensable, through its various services, to mankind. This new sweet-tasting compound was named Glycerol (derived from the Greek word glykys, which means sweet). Studies later showed glycerol to be a principal component of all fats and oils, in the form of its esters called glycerides. Glycerol was found to possess a wide variety of uses in the manufacture of numerous domestic, industrial and pharmaceutical products. Today, the name glycerol refers to the pure chemical substance and is commercially known as glycerine.
Glycerol (CH2OH.CHOH.CH2OH), in its pure form, is a sweet-tasting, clear, colorless, odorless, viscous liquid. It is completely soluble in water and alcohols, slightly soluble in many common solvents like ether and dioxane and is insoluble in hydrocarbons. At low temperatures, glycerol sometimes forms crystals which tend to melt at 17.9° C. Liquid glycerol boils at 290° C under normal atmospheric pressure. Its specific gravity is 1.26 and its molecular weight is 92.09.
Until after World War II, nearly all commercial glycerol was produced as a by-product in the manufacture of soap or from the hydrolysis of fats and oils. Today, substantial amounts of synthetic glycerol is prepared from a hydrocarbon called propylene. Crude glycerol is purified to make various grades, such as dynamite grade, yellow distilled and chemically pure glycerol. Only the highest grades of glycerol are used in foods and medicines.
Glycerol plays an important role in nearly every industry. Glycerol is used very extensively in the pharmaceutical industry. Because of its valuable emollient and demulcent properties, glycerol is an important ingredient in innumerable pharmaceutical and cosmetic preparations. Glycerine is used as a solvent in the preparation of tinctures. It is used in the preparation of Elixirs, like Theophylline, which are used to treat respiratory conditions, such as asthma and bronchitis. As a humectant, glycerol constitutes an important pharmaceutical ingredient to prevent the drying out of preparations, particularly ointments and creams. Since it is a sweet-tasting liquid it is used as a sweetening agent to impart sweetness to a preparation. It is used as a levigating agent to reduce the particle size of a drug powder. Due to its preservative qualities, it is used as a stabilizer and an auxiliary solvent in conjunction with water or alcohol. Glycerol is also used in the pharmaceutical industry to extract and prevent inert materials from precipitating upon standing. It is used as a plasticizer to enhance the spread of the coat over tablets, beads and granules.
In the food industry, glycerol is an important moistening agent for baked goods. It is also added to candies and icings to prevent crystallization. Glycerol is used as a solvent for food colors and carrier for extracts and flavouring agents. The smoothness of lotions, creams and toothpaste is due to the presence of glycerol.
Because of its humectant properties, glycerol is sprayed on pre-processed tobacco to prevent crumbling. With dibasic acids, such as phthalic acid, it reacts to make the important class of products known as alkyd resins, which are used as coatings and in paints. Glycerol draws water from its surroundings and the heat produced by the absorption makes glycerol feel warm. Due to this property, glycerol is added to adhesives and glues to keep them from drying too fast. Many specialized lubrication problems have been solved by using glycerine (glycerol) or glycerine mixtures. Many millions of pounds of glycerine are used each year to plasticize various materials, like sheets and gaskets. The flexibility and toughness of cellophane, meat casings and special quality papers can be attributed to the presence of glycerol.
The chemical industry uses glycerol in the manufacture of sealing compounds and antifreeze. Glycerol is a major starting material for nitroglycerine, also called nitroglycerol, which is used in the manufacture of dynamites and propellants. Nitroglycerine is also an active ingredient in pain-relieving drugs for heart patients. A large variety of mono- and diesters of higher fatty acids are commercially manufactured from glycerine. These esters are used as emulsifiers in foods, preparation of baked goods and modification of alkyd resins.
Glycerol aptly deserves the title 'Jack of All Trades' and is still awaiting to be of more use to mankind. Surely a substance like glycerol, which has such extensive and important uses in our everyday life, deserves a special place in the Chemistry Hall of Fame.
Glossary
Litharge: An oxide of lead (PbO) usually used in lead glazes on ceramics.
Esters: Organic compounds formed by reaction between alcohols and acids.
Hydrolysis: A chemical reaction of a compound with water. Hydrolysis of fats & oils: A reaction which cleaves an ester to give the parent acid and alcohol.
Emollient: A substance such as olive oil that has a soothing, softening effect when applied to the skin, eyes or mucous membranes. By forming an oily film, emollients prevent the loss of water from these surfaces and therefore have a moisturizing effect.
Demulcent: soothing, allaying irritation.
Elixirs: clear, sweetened hydro-alcoholic solutions which are used as oral drugs.
Humectant: Any hygroscopic substance; applied to substances added to products to keep them moist.
Levigation: Use of sedimentation or electrification to seperate finely ground particles into fractions according to their movement through a separating fluid. This method is also used in connection with wet grinding.
Plasticizer: High boiling liquids used as ingredients in lacquers and certain plastics. They do not evaporate but preserve the flexibility and adhesive power of the cellulose laquer films or the flexibility of plastic sheet and film.
Dibasic acid: An acid that has two acidic hydrogen atoms in its molecules. Examples are sulphuric acid (H2SO4) and carbonic acid (H2CO3)
Emulsifier: A compound which promotes and maintains the dispersion of finely sub-divided particles of a liquid in a vehicle in which it is immiscible.
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