Kinetic Studies and Isotope Effects of the Permanganate Oxidation of L-Phenylalanine in Acidic Medium

International Journal of Chemistry | Vol. 6, No. 10, October 2015 | pp. 73–80

DOI: 10.46882/2015/IJC/000085

Article Type: Original Research Paper

Title: Kinetic Studies and Isotope Effects of the Permanganate Oxidation of L-Phenylalanine in Acidic Medium

Names of Authors: T. M. Usman¹, F. M. Al-Rasheed²*

Authors’ Affiliations:
¹Department of Chemistry, Bayero University, Kano, Nigeria.
²Department of Chemistry, King Saud University, Riyadh, Saudi Arabia.

Abstract: The kinetics of transition metal electron transfer processes involving amino acids yield essential data required to map biochemical oxidation paths and intermediate radical formations. The oxidation of L-phenylalanine by permanganate ions (MnO₄⁻) was investigated spectrophotometrically in an aqueous sulfuric acid medium at a constant ionic strength of 0.20 M (Na₂SO₄). The reaction progress was monitored under pseudo-first-order conditions by following the absorbance decay of MnO₄⁻ at its wavelength maximum of 525 nm. The empirical rate law showed a first-order dependence on [MnO₄⁻] and a fractional-first-order dependence on [L-phenylalanine]. The reaction rate increased with rising hydronium ion concentration, revealing an acid-catalyzed pathway driven by the active protonated permanganate species, HMnO₄. Variations in ionic strength produced negligible kinetic shifts, indicating a rate-determining step involving a neutral molecule and an ionic species. Stoichiometric determinations confirmed that 5 moles of L-phenylalanine consumed 2 moles of permanganate, producing phenylacetaldehyde and Mn(II) ions as the primary end products. Thermodynamic activation constants calculated from temperature-dependence datasets using the Eyring equation yielded an enthalpy of activation (delta H*) of 45.8 kJ/mol and an entropy of activation (delta S*) of -112.4 J/mol K, supporting an inner-sphere mechanism.

Keywords: Reaction kinetics; Spectrophotometry; Permanganate oxidation; L-phenylalanine; Activation parameters; Reaction mechanisms

Manuscript Timeline: Received: March 15, 2015; Revised: May 20, 2015; Accepted: July 02, 2015; Published: October 05, 2015.

Citation: Usman, T. M., & Al-Rasheed, F. M. (2015). Kinetic Studies and Isotope Effects of the Permanganate Oxidation of L-Phenylalanine in Acidic Medium. International Journal of Chemistry, 6(10), 73–80.

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