Sugar alcohols

Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, that comprise a class of polyols. Contrary to what the name may suggest, a sugar alcohol is neither a sugar nor an alcoholic beverage. 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 is perhaps the most popular sugar alcohol due to its similarity to sucrose in visual appearance and sweetness.

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 annually. Xylitol and lacticol are obtained similarly. Erythritol on the other hand is obtained by fermentation of glucose and sucrose.

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