Ruthenium(III) Catalyzed Oxidation of Methenamine by Cerium(IV) in Aqueous Sulfuric Acid Medium—A Kinetic and Mechanistic Approach

• Published in: Russian Journal of Physical Chemistry A 2022-12, Vol.96 (13), p.2878-2886
• Main Authors: Thriveni, M. K., Shivalingaswamy, T., Bellappa, S., Mallikarjuna, I.
• Format: Article
• Language: English
• Subjects: Cerium; Chemical Kinetics and Catalysis; Chemistry; Chemistry and Materials Science; Oxidation; Oxidizing agents; Parameters; Physical Chemistry; Reaction products; Ruthenium; Spectrophotometry; Substrates; Sulfuric acid; Temperature effects
• ISSN: 0036-0244; 1531-863X
• DOI: 10.1134/S0036024422130180

Reduction of cerium(IV) when it is in the form of an oxidant is done by adding methenamine as a substrate. This can be carried out in a sulfuric acid (H + ) medium by using the method of visible spectrophotometry. The change in absorbance of oxidant at λ max 360 nm was noted as being the rate of reaction. The next reaction to be observed was the oxidation due to the presence of various experimental parameters, for example, a change in concentration of methenamine, Ce(IV), H + , and ruthenium(III). The results exhibit first-order kinetics regarding Ce(IV) and Ru(III). Also noticeable is an inverse fractional order with respect to H + in addition to the fractional order with respect to [methenamine]. A change in ionic strength ( I ) is seen to have a positive effect on the reaction rate constant. But the dielectric constant has no visible effect on the reaction velocity. Worthy of note was the rate of oxidation of methenamine which increased after the addition of Ru(III). The rate constant was deduced with respect to the cases of slow step and effect of temperature on the reaction. These had to be studied to evaluate the activation parameters. Subsequently, the reaction product was isolated and confirmed by IR studies and a suitable mechanism that was consistent with experimental observations and rate law was proposed.