Glycerol or glycerine (Propane-1,2,3-triol) is a naturally occurring colorless, odorless, viscous liquid that is a sweet-tasting and non-toxic triol compound. It occurs in nature as a triester in oils and fats. Oil and fats are triesters of glycerol with carboxylic acids. The higher fatty acid may be such as palmitic acid (C15H31COOH), steric acid (C17H35COOH), or oleic acid (C17H33COOH). A glyceride may be represented by the general formula.
Where R, R’, R” may be the same or different straight chain alkyl groups containing 12 to 18 carbons.
Structure of glycerol
The chemical structure of glycerol consists of three hydroxyl groups (-OH) attached to the carbon atoms.
Preparation of Glycerol
From oils and fats (natural production)
Glycerol is obtained on large scale as a by-product in the manufacture of soaps. Soaps are manufactured by boiling oils and fats with sodium or potassium hydroxide solution. The reaction is called saponification because the mixture of sodium or potassium salts of long-chain fatty acids is known as soap.
It can also be obtained from fats or oils by trans-esterification with methanol in the presence of an acid or a base.
From Propylene (synthetic production)
Glycerol can also be obtained on a large scale from propylene which is very cheaply obtained from the cracking of petroleum. At first, propylene is chlorinated at about 500oC to get allyl chloride which on hydrolysis with sodium carbonate solution under pressure gives allyl alcohol. The allyl alcohol is treated with chlorine water (hypochlorous acid) and subsequently hydrolyzed to get glycerol.
Metabolism of Glycerol
- Glycerol metabolism is an essential mechanism for energy generation in numerous organisms, and understanding the specific pathway involved can provide insights into the metabolic capabilities of different species.
- In mammals, glycerol is metabolized mainly in the liver, where it is converted to DHAP (dihydroxyacetone phosphate) through a series of reactions known as glycerol kinase and glycerol-3-phosphate dehydrogenase reactions.
- DHAP can then enter the glycolytic pathway and can be converted to pyruvate, which can be further metabolized to produce energy in the form of ATP.
- In the liver and adipose tissue, glycerol serves as a precursor for the production of triacylglycerols and phospholipids.
- Glycerol and fatty acids are released into the bloodstream when the body consumes stored fat as a source of energy.
- Glycerol injections are an easy way to check for liver injury since the rate of absorption by the liver is an accurate indicator of liver health.
Properties of Glycerol
- Glycerol is a colorless, odorless, and hygroscopic thick syrupy liquid having a sweet taste.
- It is non-toxic in nature.
- It boils at 290oC with slight decomposition. On cooling, it forms solid crystals having m.p. 17.9oC.
- It is soluble in water in all properties.
- Glycerol contains one secondary and two primary alcoholic groups in its molecules. It undergoes all reactions characteristic of these groups.
- Some of the reactions of glycerol are characteristic of three hydroxyl groups in adjacent positions.
- The carbon atom in glycerol is designated as α, β, α‘ or 1,2,3.
Uses of glycerol
- It is used in the manufacture of nitroglycerin, an important explosive.
- Glycerol is used as a sweetening agent in confectionary and beverages.
- It is used in the manufacture of cosmetics and high-quality soaps.
- It is used in preparations of compounds such as formic acid, allyl alcohol, etc.
- It is used as an antifreeze in automobile radiators.
- It is also used in the manufacture of glyptic resins which are used as an alkyl resin.
- It is used as a lubricant for watches and clocks.
What is glycerol?
Glycerol (Propane-1,2,3-triol) is a naturally occurring triol compound also called glycerine or glycerin.
Is glycerol a lipid?
Glycerol is categorized as a carbohydrate.
Is glycerol a carbohydrate?
As used in foods, glycerol is categorized as a carbohydrate.
What is glycerine?
Glycerine is is a naturally occurring triol compound. It occurs in nature as a triester in oils and fats.