GLYCEROL

Glycerol is a chemical compound also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. For human consumption, glycerol is classified by the FDA among the sugar alcohols as a caloric macronutrient. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. Its surface tension is 64.00 mN/m at 20 °C , and it has a temperature coefficient of -0.0598 mN/(m K). The glycerol substructure is a central component of many lipids. Glycerol is sweet-tasting and of low toxicity.

Glycerol is a 10% by-product of biodiesel production (via the transesterification of vegetable oils or animal fats). This has led to an excess of crude glycerol in the market, making the epichlorohydrin process no longer economical. Current levels of glycerol production are running at about 350,000 tons per annum in the USA, and 600,000 tons per annum in Europe. This will increase as it implements EU directive 2003/30/EC which requires replacement of 5.75% of petroleum fuels with biofuel across all Member States by 2010.

In foods and beverages, glycerol serves as a humectant, solvent and sweetener, and may help preserve foods. It is also used as filler in commercially prepared low-fat foods (e.g., cookies), and as a thickening agent in liqueurs. Glycerol also serves as a way, along with water, to preserve certain types of leaves. Glycerol is also used as a sugar substitute. In this regard, it has approximately 27 calories per teaspoon and is 60% as sweet as sucrose. Although it has about the same food energy as table sugar, it does not raise blood sugar levels, nor does it feed the bacteria that form plaques and cause dental cavities. As a food additive, glycerol is also known as E number E422.

In organic synthesis, glycerol is used as a readily available prochiral building block. Even if glycerol with no substitutions is symmetrical, and carbon atoms 1 and 3 are exchangeable, once one of them forms an ester or ether bond, the two are no longer exchangeable. Further bond formation and lysis may lead to products substituted solely at the third carbon; due to such circumstances, to maintain both full description and conformance to the chemistry naming rules (which require carbon counting to minimize ordinal numbers of substituents), the carbons are named sn-1, sn-2, and sn-3, with "sn" standing for "sterospecifical numbering".