General information about Glycerine
Propane-1,2,3-triol bears the common name glycerine. The name glycerol, by which glycerine is also known, actually has the correct ending "-ol" for an alcohol. The ending "-in" in glycerine is misleading, as it refers to alkynes or amines. The name glycerine reflects flavour and viscosity and can be traced back to the Greek word for "sweet" (glykýs) and the Latin word for "wax" (cera).
Glycerine is found naturally in most animal and vegetable fats and oils and plays a central role as an intermediate product in various metabolic processes. Triple esterified with fatty acids (triglycerides), it is part of the energy store in fatty tissue or in the seeds of oil plants such as rapeseed, soya, sunflowers, coconut or oil palms.
Bound in phosphoglycerides, glycerine enables the formation of a cell membrane. In some insects, the alcohol circulates in the blood as a natural antifreeze to enable them to survive low temperatures. Hornets can survive down to -17 degrees Celsius, the arctic ground beetle even down to -85 degrees Celsius.
Glycerine is commercially available in various purities. For industrial purposes, it is offered as 80 per cent crude glycerine and for pharmaceutical purposes (pharmaceutical glycerine) in high-purity and synthetic qualities of 99.8, 99.5 and 86 per cent.
Properties of Glycerine
At room temperature, glycerine is a colourless, odourless, sweet-tasting liquid that dissolves well in water and ethanol. However, glycerine dissolves poorly in diethyl ether and is insoluble in petrol, benzene, petroleum ether and chloroform. The sugar alcohol is the simplest trivalent alcohol, a triol. It is a slightly viscous and hygroscopic, i.e. water-attracting, liquid.
Glycerine forms white vapour when exposed to heat and flammable vapour-air mixtures at higher temperatures. The flash point is 191 degrees Celsius. If glycerine is heated in the absence of oxygen, it decomposes and the toxic aldehyde propenal is formed.
When glycerine cools down, it does not form crystals but a so-called "supercooled liquid". At -88 degrees Celsius, glycerine solidifies in a non-crystalline, amorphous structure and thus becomes a glass.
Glycerine can be oxidised, producing glyceraldehyde and dihydroxyacetone. If nitric acid reacts with glycerine, glyceric acid is formed. If a nitrating acid made from fuming nitric acid and concentrated sulphuric acid is allowed to react with glycerine, the hydroxyl groups esterify to form trisalpetric acid glycerol ester. This ester is known as nitroglycerine.
Today, glycerine is produced almost exclusively from renewable raw materials. Chemically, glycerine can be produced from propene. It is also produced during the saponification of natural fats and oils to obtain soaps. Large quantities of glycerine are produced through the transesterification of mostly vegetable oils with methanol as a by-product of biodiesel production. Biotechnological production by fermentation (Neuberg's form of fermentation) is also possible: yeasts can convert the fermentation from ethanol to glycerine by adding sulphite.
