Cocatalysts advantages

In summary, we have developed a recyclable heterogeneous catalyst for the bleach oxidation of alcohols and polyols. In contrast to previously reported systems, neither a chlorinated hydrocarbon solvent nor a bromide cocatalyst is necessary to achieve good activity. Besides bleach-oxidation, PIPO is also effective in the CuCl/nitroxyl catalysed aerobic oxidation of benzyl alcohol. A further advantage of our system is that PIPO is readily prepared from inexpensive and commercially available raw materials. We believe that it will find wide application in organic synthesis. 

A technique called "prepolymerization" is practiced with selected psd controlled catalysts used in slurry and gas phase processes. The catalyst is suspended in a suitable solvent (usually a C -C alkane) and exposed to cocatalyst, ethylene, and, optionally, comonomer and hydrogen under very mild conditions in a separate, smaller reactor (11). Prepolymerization is allowed to proceed until the original catalyst comprises 5-30% of the total weight of the composition. Prepolymerized catalysts have limited storage stability and are ordinarily introduced without delay to the large-scale reactor. Prepolymerization provides several advantages ... 

The Borstar process employs a small loop prepolymerization reactor (see section 3.6 for a discussion of the advantages of prepolymerization). Ziegler-Natta catalysts and triethylaluminum cocatalyst are commonly used but the process is capable of using single site catalysts (15). 

Epoxidations. Further utilities for the dioxirane derived from fructose is the regio-and enantioselective epoxidation of conjugated dienes and enynes. Continuing explorations of the (salen)manganese(III) systems have uncovered the catalyzed epoxidation of 2-sulfonyl-1,3-dienes at the nondeactivated sites, and the advantage of added carboxylate salt as cocatalyst. ... 

Cellulose, starch, and flour are excellently suited for immobilization of MAO because of the presence of OH groups as anchor points (Fig. 9.20). The arrangement of the OH groups on the surface possibly serves as a template for the formation of aluminoxane structures that exhibit advantageous cocatalyst properties and the activities of the resulting supported catalysts are typically in the range of 270 kg polyethylene/g Zr-h (K5ppl et al, 2001). 

The catalyst system developed at the Koninklijke/Shell Laboratorium in Amsterdam, The Netherlands, for the RIM polymerization of DCPD is WCV 2,6-diisopropylphenol (1/2) with R3SnH as cocatalyst. Both components are soluble in DCPD and have a long shelf-life. This catalyst system has the advantage of being able to polymerize DCPD of technical quality (van Deursen 1989). 

Early reports of Cu-catalyzed aerobic alcohol oxidation focused on simple homogeneous complexes [11] with nitrogenous ligands, such as 2,2 -bipyridine and 1,10-phenanthroline. However, copper-catalyzed methods that include nitroxyl radical or azodicarboxylate cocatalysts exhibit significant synthetic advantages and have been widely investigated in the literature (Figure 6.1). 

Metallocene catalysts, for example dicyclopentadienyl zirconium dichloride, in combination with the cocatalyst methylalumoxane, helped establish a regulated set of properties, making it possible to customize molar mass, molar mass distribution, tacticity, heat resistance, rigidity, hardness, cold impact strength, and transparency. Added to these advantageous physical properties is the reactivity of this catalyst... 

Advantageously, this reaction utilises a low-valent chromium complex, which reduces the catalyst s toxicity. Furthermore, this reaction proceeds without the need for a cocatalyst and at ambient pressure and temperature. From a green chemistry standpoint, these conditions are favourable and economically and environmentally feasible. This method also delivers safer reaction conditions and provides a sustainable means of trimerising ethane, completely by eliminating the use of a cocatalyst, which can cause difficulty in intermediate isolation or spectroscopic detection. 

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