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DFT Study of the Active Intermediate in the Fenton Reaction
Author(s) -
Buda Francesco,
Ensing Bernd,
Gribnau Michiel C. M.,
Baerends Evert Jan
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010702)7:13<2775::aid-chem2775>3.0.co;2-6
Subject(s) - chemistry , oxidizing agent , catalysis , photochemistry , molecule , hydroxyl radical , bond cleavage , density functional theory , primary (astronomy) , oxygen , activation energy , reaction intermediate , reaction mechanism , radical , computational chemistry , organic chemistry , physics , astronomy
Density functional theory has been used to investigate the nature of the oxidizing agent in the Fenton reaction. Starting from the primary intermediate [Fe II (H 2 O) 5 H 2 O 2 ] 2+ , we show that the oxygen–oxygen bond breaking mechanism has a small activation energy and could therefore demonstrate the catalytic effect of the metal complex. The O−O bond cleavage of the coordinated H 2 O 2 , however, does not lead to a free hydroxyl radical. Instead, the leaving hydroxyl radical abstracts a hydrogen from an adjacent coordinated water leading to the formation of a second Fe−OH bond and of a water molecule. Along this reaction path the primary intermediate transforms into the [Fe IV (H 2 O) 4 (OH) 2 ] 2+ complex and in a second step into a more stable high valent ferryl‐oxo complex [Fe IV (H 2 O) 5 O] 2+ . We show that the energy profile along the reaction path is strongly affected by the presence of an extra water molecule located near the iron complex. The alternative intermediate [Fe II (H 2 O) 4 (OOH − )(H 3 O + )] 2+ suggested in the literature has been also investigated, but it is found to be unstable against the primary intermediate. Our results support a picture in which an Fe IV ‐oxo complex is the most likely candidate as the active intermediate in the Fenton reaction, as indeed first proposed by Bray and Gorin already in 1932.