Alkaline degradation of monosaccharides III. Influence of reaction parameters upon the final product composition

Abstract

AbstractA systematic investigation of the alkaline degradation of monosaccharides is presented. The influence of several parameters upon the degradation reaction has been determined by analysis of the reaction products using HPLC and, in some cases, GC. The HO− and the monosaccharide concentrations markedly influence the final product composition with respect to both the amount of C1 to C6 acids and the formation of oligomeric acidic products, the so‐called > C6 acids. Maximum yields of these > C6 acids, up to 50 mol‐C6‐%, are obtained at an HO− concentration of between 10−3 M and 10−2 M when the monosaccharide concentration exceeds 10−2 M. The presence of divalent calcium increases the retro‐aldolization of monosaccharides in alkaline medium, as illustrated by the enhanced production of lactic acid, by complexation with, for instance, d‐fructose. Borate partly protects monosaccharides against alkaline degradation through their borate esters, whilst the amount of saccharinic acids in the degradation product mixture is doubled. On the other hand, neither chloride and carbonate nor the reaction temperature influences the final product composition. Alkaline degradation experiments with pyruvaldehyde, glyceraldehyde and 1,3‐dihydroxyacetone, all assumed to be reaction intermediates, indicate that aldolization of (di)carbonyl compounds causes the formation of substantial amounts of > C6 acids.