FUNCTIONALIZATION OF DEXTRAN - INCORPORATION OF CARBOXY GROUPS BY O-SUCCINOYLATION

The modification reaction of dextran with succinic anhydride using pyridine as catalyst and N,N-dimethylformamide/lithiumchloride system as solvent was studied. The structure of the resulting polymers was determined by means of H-1 and C-13 NMR spectroscopy. A linear dependence of the reaction rate on succinic anhydride concentration was found. The orders with respect to pyridine and polymer concentrations were 1 and 2, respectively. The activation energy was found to be 69.0 kJ/mol. C-13 NMR spectra at 75.4 MHz of partially modified dextran with monosuccinate groups were studied in order to evaluate the selectivity of the reaction of dextran with succinic anhydride in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of individual hydroxy groups decreases in the order C-2 congruent-to C-3 > C-4. For samples with higher degree of substitution the order is C-4 > C-3 > C-2. The results were explained by considering the formation of intramolecular hydrogen bonds as well as by steric considerations.