Characterization of cellouronic acid

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Intermediate structures from regenerated cellulose to water-soluble β-1,4-linked polyglucuronic acid (cellouronic acid Na salt) by TEMPO-mediated oxidation were investigated in detail using water-soluble starch as a model compound, which was oxidized stepwise from 0 to 100% oxidation by means of NMR. The results revealed that a significant amount of C6 aldehyde groups was detected as intermediate structures, which consumed the corresponding NaOH. The maximum amount of C6 aldehyde was about 40%. Sufficient reagents or sufficient reaction time gave almost pure α-1,4-linked polyglucuronic acid from water-soluble starch by TEMPO-mediated oxidation.The mechanism of depolymerization of cellulose during TEMPO-mediated oxidation was studied to control molecular weight of cellouronic acid prepared. The results indicate that hydroxyl radicals formed during the oxidation as by-products participate in the depolymerization. Some radical scavengers are effective in controlling depolymerization of ce … More llulose during the oxidation, when added to the medium. Cellouronic acid having higher molecular weight can be obtained by fractional precipitation of cellouronic acid/water solutions by gradual addition of methanol.Commercial nitroxyl radicals other than TEMPO were applied to the cellulose oxidation to see the effects on chemical structures, yields and molecular weights of the obtained products. Some nitroxyl radicals allowed to reduce reaction time required for preparing cellouronic acid from cellulose, thus giving the oxidized products having higher molecular weight. However, complete control of depolymerization could not be achieved by any treatments examined so far.TEMPO-mediated oxidation of native cellulose was investigated in detail. Although native cellulose cannot be converted to water-soluble cellouronic acid in high yields, some disordered regions undergo the oxidation to form water-soluble products. The maximum yields were ca. 20%. However, the water-insoluble residues still had the crystal structure of cellulose I, and thus oxidation to inside cellulose crystallites is difficult. Less