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The Impact of Surfactants on Fe III –TAML‐Catalyzed Oxidations by Peroxides: Accelerations, Decelerations, and Loss of Activity
Author(s) -
Banerjee Deboshri,
Apollo Frank M.,
Ryabov Alexander D.,
Collins Terrence J.
Publication year - 2009
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/chem.200900729
Subject(s) - chemistry , catalysis , hydrogen peroxide , deprotonation , bromide , medicinal chemistry , micelle , reaction rate constant , nuclear chemistry , sodium dodecyl sulfate , inorganic chemistry , organic chemistry , kinetics , aqueous solution , ion , physics , quantum mechanics
Iron(III) complexes of tetraamidato macrocyclic ligands (TAMLs), [Fe{4‐XC 6 H 3 ‐1,2‐(NCOCMe 2 NCO) 2 CR 2 }(OH 2 )] − , 1 ( 1 a : X=H, R=Me; 1 b : X=COOH, R=Me); 1 c : X=CONH(CH 2 ) 2 COOH, R=Me; 1 d : CONH(CH 2 ) 2 NMe 2 , R=Me; 1 e : X=CONH(CH 2 ) 2 NMe 3 + , R=Me; 1 f : X=H, R=F), have been tested as catalysts for the oxidative decolorization of Orange II and Sudan III dyes by hydrogen peroxide and tert ‐butyl hydroperoxide in the presence of micelles that are neutral (Triton X‐100), positively charged (cetyltrimethylammonium bromide, CTAB), and negatively charged (sodium dodecyl sulfate, SDS). The previously reported mechanism of catalysis involves the formation of an oxidized intermediate from 1 and ROOH ( k I ) followed by dye bleaching ( k II ). The micellar effects on k I and k II have been separately studied and analyzed by using the Berezin pseudophase model of micellar catalysis. The largest micellar acceleration in terms of k I occurs for the 1 a t BuOOHCTAB system. At pH 9.0–10.5 the rate constant k I increased by approximately five times with increasing CTAB concentration and then gradually decreased. There was no acceleration at higher pH, presumably owing to the deprotonation of the axial water ligand of 1 a in this pH range. The k I value was only slightly affected by SDS (in the oxidation of Orange II), but was strongly decelerated by Triton X‐100. No oxidation of the water‐insoluble, hydrophobic dye Sudan III was observed in the presence of the SDS micelles. The k II value was accelerated by cationic CTAB micelles when the hydrophobic primary oxidant tert ‐butyl hydroperoxide was used. It is hypothesized that t BuOOH may affect the CTAB micelles and increase the binding of the oxidized catalysts. The t BuOOHCTAB combination accelerated both of the catalysis steps k I and k II .