Glycerol or propane-1,2,3-triol is the only important trihydric alcohol, b.p. 290oC. It occurs in almost all animal and vegetable oils and fats as the glyceryl esters of mainly palmitic, stearic and oleic acids.

Manufacture of glycerol

Glycerol is obtained in large quantities as a by-product in the manufacture of soap, and this is still a commercial source of glycerol. It is prepared synthetically as follows:

An alternative route that is used is:

Reaction of glycerol

1.  When glycerol is treated with sodium, one α-bydroxyl group is readily attacked and the other α-group less readily; the β-hydroxyl groups is not attacked at all:


2.  On passing hydrogen chloride into glycerol at 110oC until there is the theoretical increase in weight corresponding to the esterification of one hydroxyl group, both α- and β-glycerol  monochlorohydrin are formed, the former predominating (66 per cent). Continued action of hydrogen chloride at 110oC, using 25 per cent of acid in excess required by theory for the esterification of two hydroxyl groups, produces glycerol α,α-dichlorohydrin (α-dichlorohydrin) and glycerol α,β-dichlorohydrin (β-dichlorohydrin), t he former predominating (55-57 per cent); some other products are also formed:


When either of these dichlorohydrins or glycerol itself is treated with phosphorus penta-chloride, glycerol trichlorohydirin (1,2,3-trichloropropane) is obtained. This is a liquid, b.p. 156-158oC.

3.  when glycerol is treated with monocarboxylic acids, esters are obtained which may be mono-, di- or tri-esters, according to the amount of acid used; high temperature and an excess of acid favour the formation of the tri-ester.

Use of glycerol

Glycerol is used as antifreeze, for making explosives, and because of its hygroscopic properties, as a moistening agent for tobacco, shaving soaps, etc.

Glycerol contains one secondary and two primary alcoholic groups, and it undergoes many of the reactions to be expected of these types of alcohols. The carbon atoms in glycerol are indicated as shown: αCH2OH βCHO αHorC YH2OH