Alkaline degradation reactions

Richards et al.23-24 proposed that the alkaline degradation reaction proceeds via a slow, rate-determining SJCB mechanism, where the substitution at the C-l of the D-glucose moiety by oxyanions derived from l -OH or 3 -OH resulted in 1- or 3-O-P-D-glucopyranosyl-D-fructose (see Fig. 4) the mechanism implies that T - time thyl sucrose is degraded via 3 -displacement and 3 -(3-methylsucrose via the 1 -displacement. The 1- or 3-<3-[3-D-glucopyranosyl-D-fructose intermediates are then... 

Another key factor to consider is pH since both acidic and alkaline degradation reactions can occur. 

Alkaline degradation reactions are largely controlled by the carbonyl content of cellulose (27-29). Because the carbonyl levels go up as natural aging proceeds, one should expect that an 800-year-old textile would be much more likely to be adversely affected by alkali than would new, unoxidized cellulose. The vast majority of the conservation... 

Alditols do not epimerize in oxygen-free, dilute alkaline solutions at temperatures used for alkaline-degradation reactions. 

Naturally occurring polysaccharides might be affected by alkaline solutions in places other than the reducing end. Other possible sites of reaction include (a) glycosidic linkages, which are stable to aqueous alkalis at the temperatures ordinarily used for alkaline degradation reactions [as can... 

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. 

Efficient mixing of the organic acid and the alkaline phase is essential to promote the instantaneous reaction and to avoid undesired degradation reactions in isolated acid spots and pH drift occurring in the neutralized product storage... 

Fig. 9.—Reaction model for alkaline degradation of reducing sugars.

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. 

All the membranes considered were based on quaternary ammonium groups as anion-exchange groups. However, these conductive groups may decompose in concentrated alkaline solution following the Hofmaim degradation reaction [43]. 

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