polyhydric alcohols info Chemical Man

Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, that comprise a class of polyols. They are white, water-soluble solids that can occur naturally or be produced industrially from sugars. They are used widely in the food industry as thickeners and sweeteners. In commercial foodstuffs, sugar alcohols are commonly used in place of table sugar (sucrose), often in combination with high intensity artificial sweeteners to counter the low sweetness. Xylitol and sorbitol are popular sugar alcohols in commercial foods.

Production and chemical structure

Sugar alcohols have the general formula HOCH2(CHOH)nCH2OH. In contrast, sugars have two fewer hydrogen atoms, for example HOCH2(CHOH)nCHO or HOCH2(CHOH)n−1C(O)CH2OH. The sugar alcohols differ in chain length. Most have five- or six-carbon chains, because they are derived from pentoses (five-carbon sugars) and hexoses (six-carbon sugars), respectively. They have one OH group attached to each carbon. They are further differentiated by the relative orientation (stereochemistry) of these OH groups. Unlike sugars, which tend to exist as rings, sugar alcohols do not. They can however be dehydrated to give cyclic ethers, e.g. sorbitol can be dehydrated to isosorbide.

Sugar alcohols occur naturally and at one time, mannitol was obtained from natural sources. Today, they are often obtained by hydrogenation of sugars, using Raney nickel catalysts. The conversion of glucose and mannose to sorbitol and mannitol is given:

More than a million tons of sorbitol are produced in this way every year. Xylitol and lactitol are obtained similarly. Erythritol on the other hand is obtained by fermentation of glucose and sucrose.