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Kinetics and mechanism of hydroxylamine oxidation by [Fe 2 III (µ-O)(phen) 4 (H 2 O) 2 ] 4+ in aqueous media

1998; NRC Research Press; Volume: 76; Issue: 3 Linguagem: Inglês

10.1139/v98-004

1480-3291

Beauty Chaudhuri, Rupendranath Banerjee,

Pharmaceutical and Antibiotic Environmental Impacts

Equilibrium studies show that in aqueous solutions containing excess 1,10-phenanthroline (phen) in the range pH 3-9, the complex ion [Fe 2 III ( μ-O)(phen) 4 (H 2 O) 2 ] 4+ (1) undergoes rapid but partial hydrolysis and coexists with [Fe 2 III ( μ-)(phen) 3 (H 2 O) 4 ] 4+ (1d),[Fe 2 III ( μ-O)(phen) 4 (H 2 O)(OH)] 3+ (2), and [Fe 2 III ( μ-O)(phen) 4 (OH) 2 ] 2+ (3). The solution oxidizes hydroxylamine quantitatively to N 2 O and is itself reduced to [Fe(phen) 3 ] 2+ . The reactions in the range pH 3-6 are first-order in concentrations of complex and hydroxylamine but exhibits complex [H + ] dependence, suggesting kinetic contributions from 1, 1d, and 2 but not from 3. Rapid formation of inner-sphere adducts between NH 2 OH and different {Fe 2 O} 4+ species followed by rate-determining one-electron transfer to produce NHOH and {Fe 2 O} 3+ is proposed. All subsequent steps are rapid. Ambient light does not affect kinetics and reaction products.Key words: kinetics, equilibrium, oxo bridge, iron (III), hydroxylamine.