Kinetic and Mechanistic Studies on the Oxidation of Nitrogen(III) (HNO2/) by the Tris(biguanide)manganese(IV) Ion in Aqueous Acidic Media

✍ Scribed by Amit Das; Subrata Mukhopadhyay

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: German
• Weight: 124 KB
• Volume: 88
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200590195

✦ Synopsis

Abstract

The kinetics of a net two‐electron transfer between an authentic Mn^IV^ complex, [Mn(bigH)~3~]^4+^ (Fig. 1; bigH = biguanide = C~2~N~5~H~7~), and nitrite in aqueous solution in the pH interval 2.00–3.60 is described. Stoichiometric data for the reaction clearly indicates Δ[Mn^IV^]/Δ[N^III^]~T~ = 1.07 ± 0.10, and $\rm{{{NO}}_3^ - }$ is detected as the oxidized product of nitrite ([N^III^]~T~ = [HNO~2~] + [$\rm{{{NO}}_2^ - }$]). Though both HNO~2~ and $\rm{{{NO}}_2^ - }$ are found to be reactive, the latter is kinetically superior in reducing the fully protonated Mn^IV^ complex. Proton‐coupled electron transfer (PCET; 1e, 1H^+^) reduces the activation barrier for the thermodynamically unfavorable reaction of weakly oxidizing Mn^IV^ species. At the end of the redox process, the ligand bigH is released, and the high protonation constants of the ligand carry the overall reaction to completion.