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ARTICLE

Orientation on the Mechanistics of Electron-Transfer on Oxidation of Chondroitin-4-Sulfate as Sustainable Sulfated Polysaccharide by Permanganate Ion in Aqueous Perchlorate Solutions

by Refat Hassan, Hideo Takagi, Samia Ibrahim

1 Department of Chemistry, Faculty of Science, Assiut University, Assiut, 71516, Egypt
2 Department of Chemistry, School of Science, Research Center of Materials Science, Nagoya, 464-01, Japan
3 Department of Chemistry, Faculty of Science, New Valley University, El-Kharga, 72511, New Valley, Egypt

* Corresponding Author: Refat Hassan. Email:

(This article belongs to the Special Issue: Polymer and Nanomaterials)

Journal of Renewable Materials 2020, 8(2), 205-218. https://doi.org/10.32604/jrm.2020.08530

Received 03 September 2019; Accepted 18 November 2019; Issue published 01 February 2020

Abstract

A spectrophotometric investigation of oxidation of chondroitin-4-sulfate (CS) as a sustainable and biodegradable sulfated macromolecule by oxyanion permanganate ion as multi-equivalent oxidant in acid perchlorate solutions at a constant ionic strength of 2.0 mol dm^-3 has been studied. The experimental results on the influence of the concentration of the reactants the reaction rates revealed first-order dependence in MnO₄^– , fractional second-order in [CS] and fractional first-order with respect to the hydrogen ion concentration. The hydrogen acid concentration dependence of the rate constants indicated that the oxidation rates were increased with increasing the acid concentration which means that the oxidation reaction is of acid-catalyzed nature. The oxidation of all other polysaccharides by this oxidant in acidic solutions indicated that the oxidation processes were proceeding throughout two distinct stages. The first stage was relatively slow, followed by a more fast reaction in the second stage. The addition of Mn²⁺ and F^- ions to the reaction mixtures indicated that the Mn³⁺ and/or Mn⁴⁺ as the reduced forms of permanganate were the reactive species in the second fast stage. Here, neither formation of Mn³⁺ and/ or Mn⁴⁺ transient species nor presence of two stages in the oxidation reaction were detected in the oxidation process, and this result was found to be on contrary to that observed for oxidation of all other polysaccharides by this oxidant. Formation of 1:2 coordination biopolymer intermediate complexes prior to the rate-determining step was revealed, kinetically. Identification of the oxidation product revealed the formation of keto-acid as derivative precursor of CS oxidation. This product was identified by formation of 2,4-dinitrophenyhydrazone and dioxime as wells as by the bands at frequencies 3430 (OH of COOH group); 1760-1730 cm^-1 (broad) for C=O of diketone; 1639 cm^-1 of ν_as, OCO; 1418 cm^-1 of ν_s OCO and 1338 cm^-1 of C-O-C, respectively, in the FTIR spectra. Two-electron transfer process of inner-sphere nature in the slowest step has been suggested. A tentative reaction mechanism in terms of the kinetic parameters have been suggested and discussed.

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