Production of hydrogen peroxide from dioxygen and hydroxylamine or hydrazine catalysed by manganese complexes

Selective oxidative degradation of azo dyes by hydrogen peroxide catalysed by manganese(ii) ions

“…11 show repeat UV/VIS scans (300-700 nm) of aqueous solutions of Orange II (O II, 0.100 mM ) respectively at pH For these dyes not only is there a decrease in the absorbance of the broad colour chromophore centered at ~484 nm (and shoulder at ~500 nm in the case of O II) but also a decrease in the absorbance of the naphthalene ring absorbance at ~320 nm, suggesting complete mineralisation of the dyes. These results are different to that obtained by Nunes et al using manganese(II) hydroxybenzyl-pyridyl- 15 diamine complexes in the oxidative degradation of methyl orange where there was an increase in the absorbance at ~330 nm attributed to the formation of the amine oxide.18 When the bleaching of O II and O G was attempted at pH 8.0 (phosphate or EPPS, Fig. 10 and Fig.…”

“…This six line spectrum is again 10 prominent on the addition O II (0.100 mM), yet there is no evidence for the formation of MnIV=O species at 150 mT (g ~ 4.5) in perpendicular mode nor MnIII in parallel mode at 100 mT (ESI9 †), nor any decrease in the [MnII] in a bleaching solution containing O II, as judged from the height of the peak at lowest magnetic field at ~315 mT (ESI10 †). These results are at odds with the mechanism proposed by van Eldik who implicated MnIV=O species for O II bleaching in carbonate buffer at pH 15 8.5.7 However, van Eldik did not carry out any EPR studies in his work and so the involvement of MnIV=O in these systems is somewhat speculative. A similar set of EPR spectra were obtained when O II was replaced by O G. This work suggests that MnIV=O is either not formed or is a very transient species in this system.…”

“…With both CAL and H2O2 present, there is a ~50% reduction in MnII signal, and the assumed ~50% MnII/MnIII present is due to the presence of both reduced and oxidised Mn species as coordinated CAL is 1-e-oxidised. None of the 15 EPR data shows any evidence of radical species and when CAL bleaching was repeated in the presence of an excess of the radical scavenger 2,4,6-tri-tert-butylphenol there was no reduction in the rate of oxidative degradation suggesting that the mechanism does not involve radical species e.g. •OH and •O2H.…”

Biogenic dissolution of a soil cerium-phosphate mineral

“…Complexation of humic acid, ascorbate, or citrate with Ce 3ϩ (aq) ions may have facilitated cerium oxidation, as previously described for Mn 3ϩ complexes (Morrison and others, 1977;Magers and others, 1978;Pierpont and Buchanan, 1981;Sheriff, 1992;Gelasco and others, 1998 EDTA. The accumulation of Ce (aq) after the reaction between CePO 4 ⅐ H 2 O and EDTA is comparable at pH 3, 5, or 8, and exceeds 4 x 10 -5 M (figs.…”

Coupled redox transformations of catechol and cerium at the surface of a cerium(III) phosphate mineral

“…4-8 (Morrison and Sawyer, 1977;Magers et al, 1978;Pierpont and Buchanan, 1981;Baes and Bloom, 1989;Sheriff, 1992;Gelasco et al, 1998). Complex formation results in a dramatic decrease in redox potential of Ce The production of CO 2 , oxalate, malate, and more complex forms of organic carbon following the reaction between CePO 4 ÁH 2 O and catechol indicates that catechol undergoes oxidation and oxidative polymerization because aromatic-ring rupture (Stevenson, 1994).…”