US EPA

2025759 

Journal Article 

Reaction of hydrogen peroxide with coordinated superoxide in [(NH3)(5)Co-III(mu-O-2)Co-III(NH3)(5)](5+): a mechanistic study 

Mishra, R; Mukhopadhyay, S; Banerjee, R 

2009 

Yes 

Dalton Transactions
ISSN: 1477-9226
EISSN: 1477-9234 

28 

5469-5473 

English 

19587989 

10.1039/b901280j 

WOS:000267808200008 

In aqueous acetate buffer media, hydrogen peroxide reduces the bridging superoxide in [(NH3)5CoIII(micro-O2)CoIII(NH3)5]5+ (1) to the corresponding peroxide in the complex, [(NH3)5CoIII(micro-O2H)CoIII(NH2)(NH3)4]4+ (2), itself being oxidized to HO2*. The complex 2 thus produced decomposes rapidly to the final products, CoII, NH3, etc. instead of reacting with a second molecule of hydrogen peroxide. In the presence of excess [H2O2] over (1), the reaction obeyed first-order kinetics and exhibited inverse proton dependence. [(NH3)5CoIII(micro-O2)CoIII((NH2)(NH3)4]4+ (3), a conjugate base of 1, seems to be the kinetically reactive species and the cause for the observed inverse proton dependence. Kinetics is little affected when one of the hydrogen atoms from hydrogen peroxide is replaced with an alkyl group, as in tert-butyl hydroperoxide. But replacement of both the H atoms with alkyl groups halts the reaction as seen with di-tert-butyl peroxides, and peroxodisulfate ion. The reaction rate with hydrogen peroxide significantly decreases with increasing proportion of D2O replacing water in the solvent and the rate-limiting step seems to be an H-atom transfer.