Iron-TAML activators of hydrogen peroxide: Synthesis, characterization and environmental applications.

摘要

A practical, inexpensive green chemical process for degrading environmental pollutants is greatly needed, especially for persistent chlorinated pollutants. The second chapter describes the activation of hydrogen peroxide by tetraamidomacrocylic ligand (TAML®) iron catalysts, to destroy the priority pollutants, pentachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP). In water, in minutes, under ambient conditions of temperature and pressure, PCP and TCP are completely destroyed at catalyst:substrate ratios of 1:715 and 1:2,000, respectively. The fate of ∼ 90% of the carbon and ∼ 99% of the chlorine has been determined in each case. Neither dioxins nor any other toxic compounds are detectable products, and the catalysts themselves show low toxicity.; There are various dyes and chlorinated aromatic micropollutants which are insoluble in water. Because of this insolubility, the oxidation of these compounds can become rather difficult. In most cases, organic co-solvents must be added for dissolution. A problem with the usage of co-solvents is that these substances are prone to oxidation and can compete with the desired substrate. The introduction of a surfactant to the reaction solution provides an alternative answer to this problem. The use of organized reaction media such as micelles to alter the rate and selectivity of organic and metal-catalyzed reactions is well known. Micelles are able to pre-organize reactants in ways that lead to enhanced reaction rates due to high local concentrations of reactants. In the third chapter, the use micelles and a modified activator to oxidize a water-insoluble dye in aqueous medium at neutral to slightly acidic condition is described. This study has a lot of potential as the same concept can be used to degrade significant environmental pollutants like polychlorinated dioxins and dibenzofurans.; The synthesis of stable, high valent and strongly oxidizing middle and late transition metal (MLTM) complexes is a key goal in co-ordination chemistry research. However, synthetic MLTM complexes are few, as they either reduce the high valent metal center or are unstable in the oxidation media required for formation of the high valent MLTM complexes. The Collins group has been involved in the design of robust and very strong σ-donating ligands that resist oxidative degradation. A central theme in the Collins group research program is the design and development of further generations of oxidatively robust ligands. In the fourth chapter, the synthesis of a new series of tetraamido macrocyclic ligands with an expanded ring-size (14-membered) is described. The structural, spectroscopic and hydrolytic properties of the iron and cobalt complexes of this new generation ligand are also discussed. The iron(III) complex is extremely unstable in water, rendering it inefficient as a peroxide activator in water. Hence, from the perspective of designing Fe-TAML activators that would activate H₂O₂ in water, 14-membered ring macrocycles should be avoided.