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Multistep Oxidation Kinetics of [Fe II (cdta)] [cdta = N,N′,N′′,N′′′ ‐(1,2‐Cyclohexanediamine)tetraacetate] with Molecular Oxygen
Author(s) -
Seibig Sabine,
van Eldik Rudi
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199903)1999:3<447::aid-ejic447>3.0.co;2-5
Subject(s) - chemistry , kinetics , electron transfer , oxygen , decomposition , peroxide , reaction mechanism , medicinal chemistry , organic chemistry , catalysis , physics , quantum mechanics
The complicated oxidation kinetics of the reaction of [Fe II (cdta)] [cdta = 1,2‐( N,N′ ‐ cyclohexanediamine)tetraacetate] with molecular oxygen was investigated as a function of [Fe II ], [O 2 ], pH, temperature and pressure. In the presence of an excess of [Fe II (cdta)] three steps could be observed, for which the following rate constants were found at 25°C; k 1 = 1080 ± 16 M −1 s −1 , k 2 = 103 ± 4 M −1 s −1 and k 3 = 59 ± 5 M −1 s −1 . These reaction steps can be accounted for in terms of the following mechanism: (1) [Fe II (cdta)H 2 O] 2– reacts with O 2 by a substitution process to form [Fe II (cdta)O 2 ] 2– ; (2) electron‐transfer to form an Fe III ‐superoxo species; (3) subsequent bridge formation followed by electron‐transfer to give [(cdta)Fe III ‐O 2 2– ‐Fe III (cdta)] 4– ; and (4) a fast decomposition of the peroxide intermediate yielding the monomeric [Fe III (cdta)] and H 2 O 2 . Rate and activation parameters for these steps are reported and discussed in terms of the postulated mechanism and in reference to available literature data.