Further Mechanistic Orientation on the Oxidation of Sustainable Pectin Polysaccharide by Permanganate Ion in Acidic Media

ABSTRACT The kinetics of oxidation of pectin by acidic permanganate was studied at higher concentrations of pectin, previously. Consequently, the pseudo‐first order plots of (ln (Abs. vs. time) were deviated from linearity. The results were interpreted in terms of two‐stage reactions. Therefore, the results and postulated reaction mechanism were faced some debates which means that the redox reaction needs a further investigation. We expected that deviation may be attributed to the use of pectin of high concentration which leads to the creation of some complicated intermediates. These formed complexes may tend to retard the reaction rates and, hence, the noticed deviation from linearity. Therefore, in the present work pectin substrate of low concentrations was applied to check the linearity of pseudo first‐order plots. Fortunately, all curves obtained from all plots were found to be fairly linear. This result was considered as evidence to support our expectation. Again, the experimental observations revealed second order rate constants in [H + ] on contrary to that reported previously. Such diversity and contrariety observed may indicate the complexity and non‐complementary nature of the present redox system. The activation parameters calculated by the least‐squares method from the temperature dependency of the second‐order rate constants were found to be ∆H ≠ = 52.67 kJ/mole, ∆S ≠ = –65.54 J/mole K, ∆G ≠ = 71.90 kJ/mole and E ≠ = 55.36 (±0.2–2.0 kJ/mole), respectively. However, the results obtained agreed with both inner and outer‐sphere mechanism, a simultaneous two‐electron change in one step of inner‐sphere nature was suggested to be the more preferable pathway route for the electron‐transfer. Speculated reaction mechanisms based on the experimental observations and the evaluated kinetic parameters were postulated and a pertinent discussion is presented.