KINETIC FEATURES OF THE CARBOXYMETHYLATIO N OF DEXTRAN AND THE STRUCTURE OF THE REACTION-PRODUCT

The kinetics of carboxymethylation of dextran to a degree of substitut ion DS similar to 0.8 substituted OH groups per repeat unit was studie d using UV spectroscopy and chemical analysis. The structure of the re action product was examined with 1D and 2D H-1 NMR and C-13 NMR. From the very start of the reaction, three monosubstituted rings are identi fied; beginning from DS similar to 0.30-0.35, three disubstituted ring s are also detected. The rate coefficients for monosubstitution of the OH groups at C2, C3, and C4 decrease in the order k(2) > k(4) > k(3). Monosubstitution reduces by similar to 50% the reactivity of the OH g roup in the beta-position and by similar to 30% the reactivity of the OH group in the gamma-position. At DS > 0.3, the rate coefficient decr ease with conversion. The specific features of the reaction that were interpreted in terms of typically polymeric effects, such as the charg ed coil effect and the interaction between the neighboring rings (form ation of H-bonds between the units).