title: Reactivity and operational stability of N-tailed TAMLs through kinetic studies of the catalyzed oxidation of orange II by H2 O2 : synthesis and X-ray structure of an N-phenyl TAML.
abstract: The catalytic activity of the N-tailed ("biuret") TAML (tetraamido macrocyclic ligand) activators [Fe{4-XC6 H3 -1,2-(NCOCMe2 NCO)2 NR}Cl](2-) (3; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me (a); NO2 , Me (b); H, Ph (c)] in the oxidative bleaching of Orange II dye by H2 O2 in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4-XC6 H3 -1,2-(NCOCMe2 NCO)2 CMe2 }OH2 ](-) (1) and the more aggressive analogue [Fe(Me2 C{CON(1,2-C6 H3 -4-X)NCO}2 )OH2 ](-) (2). Catalysis by 3 of the reaction between H2 O2 and Orange II (S) occurs according to the rate law found generally for TAML activators (v=kI kII [Fe(III) ][S][H2 O2 ]/(kI [H2 O2 ]+kII [S]) and the rate constants kI and kII at pH 7 both decrease within the series 3 b>3 a>3 c. The pH dependency of kI and kII was investigated for 3 a. As with all TAML activators studied to-date, bell-shaped profiles were found for both rate constants. For kI , the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a. For kII , the broad bell pH profile exhibits a maximum at pH about 10.5. The condition kI ≪kII holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants ki for suicidal inactivation of the active forms of complexes 3 a-c were calculated using the general formula ln([S0 ]/[S∞ ])=(kII /ki )[Fe(III) ]; here [Fe(III) ], [S0 ], and [S∞ ] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X-ray characterization of 3 c are also described.
authors: Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA, 15213 (USA).
authors: Genoa R
authors: GR
authors: Warner
authors: Matthew R
authors: MR
authors: Mills
authors: Clarissa
authors: C
authors: Enslin
authors: Shantanu
authors: S
authors: Pattanayak
authors: Chakadola
authors: C
authors: Panda
authors: Tamas Kumar
authors: TK
authors: Panda
authors: Sayam Sen
authors: SS
authors: Gupta
authors: Alexander D
authors: AD
authors: Ryabov
authors: Terrence J
authors: TJ
authors: Collins
mesh_terms: D000577:Amides / Q000737:chemistry*; D001391:Azo Compounds / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction
chemical_list: D000577:Amides; D001391:Azo Compounds; D001557:Benzenesulfonates; D008024:Ligands; D047028:Macrocyclic Compounds; D006861:Hydrogen Peroxide; C014722:2-naphthol orange
keywords: hydrogen peroxide; iron; kinetics; oxidation; reaction mechanisms