Base-catalyzed oxidation of some anionic polyelectrolytes: Kinetic and mechanistic aspects to electron-transfer process into hexacyanoferrate(III) oxidation of alginate polysaccharide in alkaline media

• Orientation into electron-transfer nature for oxidation of alginates by alkaline hexacyanoferrate(III).
• Kinetics and mechanistic aspects for such redox reaction.
• A novel synthesis of diketo-derivatives of alginates by oxidation method.
• Examining the behavior of anionic polyelectrolytes in aqueous alkaline solutions.

The kinetics and mechanism of oxidation of alginate polysaccharide (Alg) by alkaline hexacyanoferrate(III) in basic solutions at a constant ionic strength of 1.0 mol dm−3 have been investigated spectrophotometrically. The experimental results showed complex kinetics, where the reaction time curves of the pseudo first-order plots were found to be of sigmoidal S-shape nature. The initial parts of the plots were relatively fast, followed by slow-linear portions after short time periods. The oxidation rates were increased with increasing the alkali concentration indicating that the oxidation is base-catalyzed. A kinetic evidence for formation of 1:1 intermediate complexes was revealed. The activation parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.

The kinetics and mechanism of oxidation of alginate polysaccharide (Alg) as anionic polyelectrolyte by alkaline hexacyanoferrate(III) have been investigated spectrophotometrically. The experimental results showed complex kinetics where the pseudo first-order plots were found to be sigmoidal of S-shape character. The oxidation rates were increased with increasing the alkali concentration, i.e. the oxidation is base-catalyzed. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.Figure optionsDownload high-quality image (86 K)Download as PowerPoint slide