Structural modification of potato starch by solutions of nitrogen(IV) oxide in CCl4

Abstract

Structural transformations of potato starch by solutions of nitrogen(IV) oxide in CCl 4 were studied as a function of oxidant concentration, starch moisture content, reaction time, and molar ratio of reactants. Oxidized starches with various numbers of carboxylic acids were studied by x-ray phase analysis, 13 C NMR, and IR spectroscopy. It was found that carboxylic acids were formed primarily on C 6 in starch oxidation products that were x-ray amorphous. The number of carboxyls increased slightly with increased oxidation time and oxidant concentration. It was shown that moisture must be present in the starch for oxidation by nitrogen(IV) oxide to be effective.Starch production has recently become more interesting [1-6] because modified starches have a unique set of physical chemical properties and the starting material can be constantly renewed.The goal of the present work was to investigate the effect of various factors on oxidative transformations of starch by solutions of nitrogen(IV) oxide (N 2 O 4 ) in CCl 4 .Starch oxidation by N 2 O 4 follows mainly the following scheme:A study of the effect of the glucopyranose unit (GPU):N 2 O 4 mole ratio at constant N 2 O 4 concentration ( Fig. 1) on the rate of oxidative transformations of the polysaccharide revealed the effect of the reaction products (NO, H 2 O, HNO 3 , N 2 O 3 , HNO 2 ) on the reaction. The higher the mole ratio of reactants, the lower the oxidant concentration and the change of composition during the reaction. Increasing the amount of oxidant under otherwise equal conditions increased both the rate and the maximum degree of starch oxidation in the studied time interval. Further increasing (>10 moles) the excess of oxidant had no effect on the process. Therefore, all subsequent kinetic studies were carried out with a 10-fold excess of N 2 O 4 relative to the stoichiometric amount required for full oxidation of the primary hydroxyls to carboxylic acids.The results show ( Table 1) that changing the N 2 O 4 concentration from 5 to 20 mass % with a constant mole ratio of reactants increased the oxidation and the reaction rate to their upper limits. This can be explained by the activating action of N 2 O 4 , which can cleave intermolecular H-bonds and increase the rate of diffusion processes close to the quasihomogeneous value by penetrating into the starch granules. The activating action of N 2 O 4 is quite consistent with the observed morphology change of the starch granules (Fig. 2). As the N 2 O 4 solution concentration increased, the starch granules underwent greater changes.

Cellulose oxidation by Laccase-TEMPO treatments

“…These chemical oxidants can be divided into non-selective, such as nitrogen oxides (Butrim,58 Bil'dyukevich, Butrim, & Yurkshtovich, 2007), alkali metal nitrites and nitrates (Painter, n.d.), 59…”