3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

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Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Cognitive architecture of a mini-brain: the honeybee

This review describes examples of remarkable acceleration of metal-catalyzed oxidation reactions by certain additives. In some cases, reactions proceed 2 or 10 times more rapidly in comparison with the process in the additive’s absence, in other cases, reactions become possible only in the presence of the additive. Varying ligands at the metal center or additives, one can not only dramatically improve yields of oxygenates but also control the selectivity of the reaction. Understanding mechanisms of the additive’s action is very important for search of new efficient catalysts and catalytic systems. Additives considered in the review can play roles of the ligands at metal ion or proton or electron transfer reagents and they mimic certain enzymes (the active center or its environment). Often the mechanism of the effect of additives on the reaction rate and the product yield is unknown, and the main aim of the review is to attract investigator’s attention in creating new efficient catalytic systems, which contain not only a metal ion but also a necessary “additive”.

http://shulpin.narod.ru/JMolCatal2002.pdf

Metal-catalyzed hydrocarbon oxygenations in solutions: the dramatic role of additives: a review

Recent developments on the epoxidation of alkenes using hydrogen peroxide as an oxidant

From an economic perspective, textile and paper bleaching are amongst the most important oxidation processes. The removal of unwanted chromophores, be it stains on cloths or residual lignin in wood pulp, consumes more than 60 % of the world production of hydrogen peroxide. However, existing technologies have their limitations. At ambient temperature, hydrogen peroxide gives little stain bleaching and is used inefficiently. Hence the high product dosages and washing temperatures required limit its application to predominantly European markets, to the exclusion of the majority of the world's population. In paper manufacture, the use of chlorine-based oxidants results in the formation of chlorinated waste products, which show poor biodegradability. On the other hand, hydrogen peroxide requires higher temperatures, longer reaction times and is more expensive. Transition-metal catalysts offer an alternative. This review discusses the main classes of known bleach catalysts and their possible modes of action.

Applications of Transition-Metal Catalysts to Textile and Wood-Pulp Bleaching

THE detergents of the next century will be routinely required to contain bleaching agents that are not only more active than those currently available but also environmentally safe and cost-effective. Hydrogen peroxide, the traditional bleaching agent1, loses its activity as the washing temperature decreases. Peroxyacetic acid maintains acceptable bleaching activity down to 40–60 °C (ref. 2), but still lower temperatures are desirable. It is generally recognized that manganese and iron complexes are less environmentally damaging reagents than other transition-metal compounds, and such complexes have received considerable attention as bleaching catalysts3–11. Here we show that manganese complexes derived from l,4,7-trimethyl-l,4,7-triazacyclononane and related ligand systems act as highly effective catalysts for the bleaching of stains by hydrogen peroxide at low temperatures. These complexes also catalyse the epoxidation of alkenes and the oxidation of poh phenolic substrates by hydrogen peroxide. Our results demonstrate the considerable potential of these systems for clean and efficient low-temperature bleaching.

M. Robert P. van Vliet

Papers

Efficient manganese catalysts for low-temperature bleaching