Modifications aldonic acid

PolysuWde Process. One modification to the kraft process being appHed commercially is the polysulfide process (38). Under alkaline conditions and relatively low temperature (100—120°C), polysulfides oxidize the active end group of the polysaccharide polymer to an alkaH-stable aldonic acid. This reaction, known for many years (39), was not produced on a commercial scale until the development of an efficient method for in situ generation of the polysulfide in kraft white Hquor. 

The aldehydo acetates have been oxidized to the corresponding aldonic acids without deacetylation by the action of bromine in the presence of potassium bicarbonate. In this manner. Major and Cook obtained pentaacetyl-D-gluconic acid. A modification of this method was used by Wolfrom, Brown and Evans for the preparation of pentaacetyl-D-galactonic acid. 

It was known that aldoses could be reduced to alditols, and could be oxidized to the monocarboxylic aldonic acids and to the dicarboxylic aldaric acids. A theory of stereoisomerism and optical activity had been proposed (1874) by van t Hoff and Le Bel. Methods for separating stereoisomers were known and optical activity could be measured. The concepts of racemic modifications, meso compounds, and epimers were well established. 

The halogens and their oxyacids probably are the most important oxidants used in the carbohydrate field. They are widely used as bleaching agents, but the mechanism of this action remains to be clarified. As reagents for preparatory purposes (particularly for aldonic acids and lactones) and for analytical procedures, they are very important. Periodic acid, discussed in a later section, has an important application for the elucidation of structures of carbohydrates. A number of valuable commercial products are made by treatment of polysaccharides with halogens, particularly chlorine or hypochlorous acid, but the nature of these actions, such as the modification of starch, has not been clarified. 

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