These are also known as phosphatides. They are an important compound, composed of fatty acid, glycerol, phosphoric acid, and nitrogenous base.

These are the lipids which contain certain chemical groups others than alcohol and fatty acid. Compound lipids include phospholipid, glycolipids, sulpholipids, and lipoproteins.

Glycerol is utilised in the body as follows: Glycerol is phosphorylated to form phosphoglycerate (glycerophosphate) action of ATP and specific phosphokinase. Glycerophosphate is oxidised to glyceraldehyde-3-phosphate, which is an intermediate in glycolysis, which is further oxidised to yield energy. Glycerol is widely used as solvent in the manufacturer of cosmetics and in the preparation of…

Oxidation: When glycerol is oxidised with H2O2 in slight alkaline solution in the presence of iron salt, a mixture of trioses, glyceric aldehyde, and dihydroxy acetone is formed. Acrolein formation: When glycerol is heated either alone or in the presence of dehydrating agent like KHSO4, a substance called acrolein, which is an unsaturated aldehyde, is obtained.

Physical Properties It is colourless heavy liquid with specific gravity of 1.26. It is sweetish in taste and is commonly known as glycerine. It is soluble in water and alcohol but insoluble in lipid solvents like ether, chloroform, and benzene.

Glycerol is a component of fat. Its properties and reactions are described below. Glycerol is commonly called glycerine and is the alcoholic component of triglycerides. It is closely allied to carbohydrates in its chemical structure and properties, but it is closely associated with fats in its occurrence and function. The structure of glycerol is given below:

Addition reaction Isomerism: Unsaturated fatty acids may have isomers, depending upon two factors. One type of isomerism depends upon the position of double bond in the hydrocarbon chain – positional isomerism. Example: Oleic acid. There are sixteen positions where the double bonds may be placed. Hence, oleic acid forms sixteen isomers. Geometrical isomerism: It depends on the oxidation…

These are mainly due to the double bonds contained in the chain.

The carboxyl group condenses with alcohol to form esters. Triglyceride is an ester of fatty acid with glycerol. Cholesterol ester is formed by esterification of fatty acid with cholesterol. They are present in blood. The carboxyl group may be reduced to the corresponding aldehydes and alcohols in the presence of hydrogen at high temperature.

Soap formation: Fatty acids form salts (soaps) with alkalis because of the presence of a terminal carboxyl group.   RCOOH + NaOH  RCOONa + H2O