Peeling reactions, alkaline degradation

The end group which is produced contains a carboxylic acid functionality which has an influence on the anionicity of pulp fibres (Chapter 6) but, in this form, it is resistant to further alkaline degradation. The hemicelluloses are also able to undergo the same type of peeling reaction but at different rates from each other and from cellulose. The /3-1,4-xylans, for example, are more stable to alkaline degradation than the glucomannans. 

Anion-exchange resins may be used for the peeling-type of alkaline-degradation reactions, as shown by the formation of D-glucose from tu-ranose - (S-O-a-D-glucopyranosyl-D-fructose) on treatment with such materials. 

According to Scheme 12, the alkaline peeling of cellulose should continue until the entire polymer is degraded. However, cellulose dissolves partially, but not completely, in hot alkali, and this remaining polysaccharide contains an increased carboxyl content.Thus, a second reaction is occurring that competes with the step-wise, peeling procedure. 

Lactulose is unstable in alkaline solution, degrading by alkaline peeling and /3-elimination reactions to yield galactose, isosaccharinic acids, and other acid products (Corbett and Kenner 1954). Amines can bring about dehydration and degradation reactions (Hough et al. 1953). Lactulose is similar to sucrose in humectant properties (Huhtanen et al. 1980). 

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