Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML1. Issue 16 (13th February 2015)

• Record Type: Journal Article
• Authors: Warner, Genoa R.; Mills, Matthew R.; Enslin, Clarissa; Pattanayak, Shantanu; Panda, Chakadola; Panda, Tamas Kumar; Gupta, Sayam Sen; Ryabov, Alexander D.; Collins, Terrence J.
• Is Part Of: Chemistry. Volume 21:Issue 16(2015)
• Page Start: 6226
• Page End: 6233
• Publication Date: 2015-02-13
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201406061
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The catalytic activity of the <italic>N</italic>‐tailed ("biuret") TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC<sub>6</sub>H<sub>3</sub>‐1, 2‐(<bold>N</bold>COCMe<sub>2</sub><bold>N</bold>CO)<sub>2</sub>NR}Cl]<sup>2−</sup> (<bold>3</bold>; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds <bold>1</bold> and <bold>2</bold> below), [X, R=H, Me (<bold>a</bold>); NO<sub>2</sub>, Me (<bold>b</bold>); H, Ph (<bold>c</bold>)] in the oxidative bleaching of Orange II dye by H<sub>2</sub>O<sub>2</sub> in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC<sub>6</sub>H<sub>3</sub>‐1, 2‐(<bold>N</bold>COCMe<sub>2</sub><bold>N</bold>CO)<sub>2</sub>CMe<sub>2</sub>}OH<sub>2</sub>]<sup>−</sup> (<bold>1</bold>) and the more aggressive analogue [Fe(Me<sub>2</sub>C{CON(1, 2‐C<sub>6</sub>H<sub>3</sub>‐4‐X)<bold>N</bold>CO}<sub>2</sub>)OH<sub>2</sub>]<sup>−</sup> (<bold>2</bold>). Catalysis by <bold>3</bold> of the reaction between H<sub>2</sub>O<sub>2</sub> and Orange II (S) occurs according to the rate law found generally for TAML activators (<italic>v</italic>=<italic>k</italic><sub>I</sub><italic>k</italic><sub>II</sub>[Fe<sup>III</sup>][S][H<sub>2</sub>O<sub>2</sub>]/(<italic>k</italic><sub>I</sub>[H<sub>2</sub>O<sub>2</sub>]+<italic>k</italic><sub>II</sub>[S]) and the rate constants <italic>k</italic><sub>I</sub> and <italic>k</italic><sub>II</sub> at pH 7 both decrease within the series <bold>3 b</bold>><bold>3 a</bold>><bold>3 c</bold>. The pH dependency of <italic>k</italic><sub>I</sub> and <italic>k</italic><sub>II</sub> was investigated for <bold>3 a</bold>. As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For <italic>k</italic><sub>I</sub>, the maximal activity was found at pH 10.7 marking it as having similar reactivity to <bold>1 a</bold>. For <italic>k</italic><sub>II</sub>, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition <italic>k</italic><sub>I</sub>≪<italic>k</italic><sub>II</sub> holds across the entire pH range studied. Activator <bold>3 b</bold> 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 <italic>k</italic><sub>i</sub> for suicidal inactivation of the active forms of complexes <bold>3 a</bold>–<bold>c</bold> were calculated using the general formula ln([S<sub>0</sub>]/[S<sub>∞</sub>])=(<italic>k</italic><sub>II</sub>/<italic>k</italic><sub>i</sub>)[Fe<sup>III</sup>]; here [Fe<sup>III</sup>], [S<sub>0</sub>], and [S<sub>∞</sub>] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of <bold>3 c</bold> are also described.</p> </abstract>