Description
Glycerine (glycerol, propane-1,2,3-triol, C₃H₈O₃) is an organic chemical substance from the group of sugar alcohols. It is the simplest stable trihydric alcohol. Glycerine is a colorless, transparent, syrupy liquid with strong hygroscopic properties. It is greasy to the touch but mixes with water without restrictions. In addition, it is strongly hydrophilic, and is used as a marker of the highest hydrophilicity on the scale of miscibility of organic solvents (value 1). In cosmetics, glycerine is often used as a moisturizing ingredient in various products, such as skin care creams, soaps or shampoos. In the food industry, it is used as a sugar substitute, a humectant or a thickener in food products, such as cakes, ice cream or jams. Glycerine can also be used in other industries, such as pharmaceuticals or chemicals, due to its moisturizing and stabilizing properties. However, the uses of glycerin also depend on its concentration. Glycerine 80% is technical glycerine, often used as a raw material or in the chemical industry. It may contain impurities. Glycerine 96% and 99% have a higher degree of purity and are used in the pharmaceutical, food and cosmetic industries.
In industry, glycerine is often obtained from vegetable and animal fats, which, in reaction with alkali solutions, undergo hydrolysis to glycerine and soaps. This reaction takes place in the presence of water and at high pressure and high temperature. In practice, this process takes place in autoclaves, in the presence of catalysts such as hydroxides. Glycerine is also produced as a by-product in the production of biodiesel. During the transesterification of animal or vegetable fats with alcohol (e.g. methanol), biodiesel and glycerine are produced. The glycerine then requires purification. Moreover, the chemical naturally occurs in some fruits and vegetables. A less frequently used method of obtaining glycerine is the chemical synthesis processes from propylene, a petroleum derivative. Propylene can be oxidized to glycerol in several stages, for example by oxidation to epichlorohydrin and then hydrolysis. However, this is an expensive process,
Typical glycerin reactions are able to occur due to the presence of three hydroxyl groups (-OH). Glycerine undergoes an esterification reaction, reacting with organic acids (e.g. fatty acids) and creating esters called triacylglycerols (fats). Similarly, in the presence of sulfuric acid as a catalyst, glycerine reacts with nitric acid to form nitroglycerine – a substance used in dynamite. In the presence of hydroxides (alkaline environment) and a strong oxidant, glycerine undergoes transformation into aldehydes and organic acids. In addition, it is also capable of undergoing combustion. In the presence of acids, glycerine’s dehydration, i.e. deprivation of water, occurs. This results in the formation of acrolein (propenal), a substance with an intense smell. It also reacts with halides and some metals: for example, when it reacts with copper(II), a blue-coloured compound is formed, which is used in chemical analysis.
