Synthesis, Properties, and Reactivity of Sulfonamide NewTAML Oxidation Catalysts
thesis
posted on 2019-10-29, 18:34 authored by Genoa
R. WarnerWorldwide, water is becoming increasingly contaminated with micropollutants, substances present at low concentrations that have undesired effects. Conventional
wastewater treatments are ineffective against many of these hormones, pesticides, pharmaceuticals, personal care products, and other commonplace chemicals. TAML
activators, small-molecule peroxide-activating oxidation catalysts, are one solution for removing organic pollutants during water purification. TAML activators have been
iteratively improved over the past twenty years to be highly reactive, easy to prepare, and resistant to oxidation. However, modifications to the macrocyclic ligand such as the biuret tail have not significantly improved reactivity or lifetime. Further investigation into the structural source of the lifetime limitation of TAMLs has led to the design of
“NewTAML” activators, a new family of catalysts featuring sulfonamides (–NHSO2–) instead of carbonamides (–NHCO–) in the ligand. NewTAMLs are comprised of
biochemically common elements, are cheaper to produce than our prior best-performing, fluorine-containing TAMLs, and are significantly more reactive—the concentrations
employed in the presented model pollutant removal studies translate to one kilogram of catalyst treating 16,000–160,000 tonnes of municipal wastewater.
Seven NewTAML activators have been prepared and thoroughly characterized through various techniques including X-ray crystallography. NewTAML activators
follow the accepted mechanism of catalysis established for previous “OldTAMLs.” In the bleaching of the model substrate Orange II, all NewTAMLs perform superiorly compared to their structural analogs at neutral pH. The electron-withdrawing sulfonamide groups in NewTAMLs increase the Lewis acidity of the metal resulting in decreased axial water pKa by 1.2 units. The pH dependence of catalyst activity reveals that the decrease in pKa
has shifted maximum reactivity toward neutral pH. Additionally, NewTAMLs are ten times more resistant to specific acid demetalation at low pH and show no toxicity toward prepubertal mice. Lifetime studies of NewTAMLs reveal that these catalysts contain a significant pH-dependent inactivation pathway that limits the utility of NewTAMLs at pH 9 and above. This inactivation is presumably associated with deprotonation of the
acidic methylene tail in the active state. However, CH3 for H substitution at the tail substantially reduces this inactivation pathway. Overall, NewTAMLs are highly reactive,
easy to prepare oxidation catalysts with promise for water treatment applications.
wastewater treatments are ineffective against many of these hormones, pesticides, pharmaceuticals, personal care products, and other commonplace chemicals. TAML
activators, small-molecule peroxide-activating oxidation catalysts, are one solution for removing organic pollutants during water purification. TAML activators have been
iteratively improved over the past twenty years to be highly reactive, easy to prepare, and resistant to oxidation. However, modifications to the macrocyclic ligand such as the biuret tail have not significantly improved reactivity or lifetime. Further investigation into the structural source of the lifetime limitation of TAMLs has led to the design of
“NewTAML” activators, a new family of catalysts featuring sulfonamides (–NHSO2–) instead of carbonamides (–NHCO–) in the ligand. NewTAMLs are comprised of
biochemically common elements, are cheaper to produce than our prior best-performing, fluorine-containing TAMLs, and are significantly more reactive—the concentrations
employed in the presented model pollutant removal studies translate to one kilogram of catalyst treating 16,000–160,000 tonnes of municipal wastewater.
Seven NewTAML activators have been prepared and thoroughly characterized through various techniques including X-ray crystallography. NewTAML activators
follow the accepted mechanism of catalysis established for previous “OldTAMLs.” In the bleaching of the model substrate Orange II, all NewTAMLs perform superiorly compared to their structural analogs at neutral pH. The electron-withdrawing sulfonamide groups in NewTAMLs increase the Lewis acidity of the metal resulting in decreased axial water pKa by 1.2 units. The pH dependence of catalyst activity reveals that the decrease in pKa
has shifted maximum reactivity toward neutral pH. Additionally, NewTAMLs are ten times more resistant to specific acid demetalation at low pH and show no toxicity toward prepubertal mice. Lifetime studies of NewTAMLs reveal that these catalysts contain a significant pH-dependent inactivation pathway that limits the utility of NewTAMLs at pH 9 and above. This inactivation is presumably associated with deprotonation of the
acidic methylene tail in the active state. However, CH3 for H substitution at the tail substantially reduces this inactivation pathway. Overall, NewTAMLs are highly reactive,
easy to prepare oxidation catalysts with promise for water treatment applications.
History
Date
2017-07-31Degree Type
- Dissertation
Department
- Chemistry
Degree Name
- Doctor of Philosophy (PhD)