It is present in all oils and fats which are esters of glycerol (alcohol) with higher fatty acids, e-g palmitic, stearic and oleic acids. Oils and fats are industrially used for the manufacture of soaps and candles, glycerol is obtained as a by product in each case. In soap manufacture, oils are hydrolysed in presence of alkali (NaOH) while in candle industry, oils are hydrolysed with steam.
(R1, R2 and R3 may be similar or different)
Filtrate after removing soap contains mainly glycerol and known as spent lye.
\(Oil \xrightarrow{steam}Fatty\,acids+Glycerol\)
Fatty acids are removed and mixed with paraffin wax to get candles. Product obtained after removing fatty acids mainly contains glycerol and known as sweet water.
Synthetic glycerol is obtained industrially from propene (CH3CH = CH2).
It is sweet in taste and miscible with water and highly viscous. Pure glycerol decomposes at its Glycerol b.p., hence it is purified by distillation under reduced pressure (vacuum distillation). It has two primary (-CH2OH) and one secondary (-CHOH) alcoholic groups. Its important reactions are mentioned below.
(i) Reaction with HI (or P4 + I2) gives allyl iodide (CH2 = CHCH2l) which may further react with HI to give isopropyl iodide (CH3.CHI. CH3).
So remember that allyl iodide, propene and isopropyl iodide are formed depending upon the amount of HI used.
(ii) On reduction with HI, it gives propane as the final product
(iii) Reaction with nitric acid gives glyceryl trinitrate (nitroglycerine or Noble oil), used in the manufacture of explosives like dynamite, cordite, blasting gelatin etc. Glyceryl trinitrate is also used in the treatment of angina pectoris and asthma. Dynamite is nitroglycerine adsorbed on kieselguhr. It is a safer explosive.
Blasting gelatin is a mixture of nitroglycerine with cellulose nitrate (gun cotton). Cordite is a mixture of nitroglycerine with cellulose nitrate and vaseline. It is a smokeless powder.
(iv) Reactions with oxalic acid at 110°C and 260°C give formic acid (HCOOH) and allyl alcohol (CH2 = CHCH2OH) respectively.
(v) Dehydration (-H2O) with potassium hydrogen sulphate (KHSO4), conc. H2SO4 or P2O5 gives acraldehyde (acrolein, CH2 = CHCHO).
