Sugar alcohol

Alditols are acyclic polyols with the formula HOCH 2 [CH (OH)] nCH2OH derived structurally as reduction products of carbohydrates ( sugar). They are also referred to as sugar alcohols.

Structure

The alditols include, for example mannitol ( mannitol), isomalt, lactitol, sorbitol ( Sorbitol or glucitol ) and xylitol ( Xylitol ), threitol, erythritol and arabitol.

The name of the alditols follows the following convention: The ending- ose (eg glucose ) of the original sugar by the ending -it ( glucitol ) or ITOL ( glucitol ) is replaced. As there are some alditols derived from both aldoses and ketoses formal, it happens that a alditol carries several names, such as glucitol and sorbitol refer to the same substance.

Due to the general structure of the glycerol can be formally regarded as the simplest, derived from glyceraldehyde alditol. The simplest chiral alditol is the threitol, which of the Threose, a carbohydrate with four carbon atoms, derived. From erythrose, is also a carbohydrate having four carbon atoms, the erythritol derives, in contrast to the threitol optically inactive ( meso compound ).

Properties

The flavor profile of alditols similar to that of sucrose, however, is not the same. They taste sweet but rarely to the relative sweetness of sucrose are non-cariogenic and show a laxative effect at a consumption of more than 20 to 30 g per day. Some alditols are used as sugar substitutes in dietetic foods because they do not raise blood sugar levels and do not require insulin to be dismantled. Therefore they are suitable for diabetics.

Differences between alditols and sucrose are still to be found in the solubility, the pH and the temperature stability, the melting point and the boiling point. These factors are crucial for their technical use in food.

Synthesis

Alditols can be prepared from aldoses or ketoses, by reduction of the carbonyl group. This is accomplished by catalytic hydrogenation over a nickel catalyst, industrially. In this manner, D-sorbitol is synthesized from D-glucose. On a laboratory scale, the sodium borohydride ( sodium borohydride, NaBH4 ) is suitable as a reducing agent.

Since in the reduction of aldoses the stereocenters are not changed, a alditol is exactly formed from an aldose. However, the same alditol from two different aldoses produce:

The L- gulose shown in the 180 ° rotated Fischer projection in the above scheme therefore provides for reducing also D- sorbitol.

The reduction of ketoses, however, generates a new stereogenic center in two possible configurations, so that from a ketose a mixture of two different ( epimeric ) alditols is formed:

Since their separation causes significant processing costs, some alditols also be produced by biocatalytic reaction with living microorganisms.

Use

Alditols are primarily used in the food industry, where they are used as sweeteners. Especially sorbitol has a wide range of applications, from the use as a sugar substitute and uses in the cosmetics industry and as a sweetener for toothpaste to humectants for tobacco, building materials and additives uses in the chemical industry bsp. for the production of nitro orbit, surfactants, polyols for polyurethanes ranges.