Scavenging with Functionalized Silicas

In the case of batch processing the scavenger is added to the reaction mixture after completion. For flow-through processing the scavenger is packed into a column (solid-phase extraction, HPLC, etc.) and the reaction mixture is passed through the column until scavenging is complete. 

Standard purification procedures including chromatography, liquid-liquid extraction and crystallization can be time consuming and difficult to scale up. In many cases supported reagents have distinct advantages over their solution-phase counterparts, including increased selectivity, 

The silica-based scavenger has much faster kinetics which allows it to scavenge HOBt in only five minutes (Table 3.1). 

Compared to scavenging using the bulk product, scavenging of HOBt over a column packed with silica-functionalized carbonate (SiliaPrep Carbonate) enables optimal sequestration with only 5 ppm of residual peroxide from a 5000 ppm HOBt solution (Table 3.2) 4 

Solid-phase extraction media Time (min) HOBt removed1 (%) 

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Comparable results were achieved with the silica-based diamine (3.0 equivalents of the amine functionality). At room temperature, the excess anhydride was scavenged within 4 h. On the other hand, microwave heating at 100 °C in a sealed ves-... 

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

One way of separating the scavenging function of cocatalysts from their chemical influence (reduction and alkylation) is to use solid cocatalyst. For example, partially dehydroxylated silica can be treated with... 

In addition to the silica or polymer based resins mentioned above, polymer based resins with specific chemistries at the functional group have also been widely used as palladium scavengers for synthetic organic reactions. These include macroporous polystyrene-bound trimercaptotriazine (TMT). It, along with the thiol resin, has been found to be highly effective in reducing the concentration of palladium in both aqueous and non-aqueous solutions [18]. 

Mediators of both the infiammatoiy and fibrotic responses have been associated with exposure to oxidants. Similarly, mediator release after incubation of cells with silica and asbestos can be the result of oxygen-based free radicals catalyzed by iron associated with the mineral oxide (Fig. 1). The increase in arachidonic acid metabolism after exposures of cells to particles and fibers can result from the eooxidation of arachidonate by metal-catalyzed oxidants. This is a lipid peroxidation that can be mediated by free radical production by the dust (83). In support of an association between metal-catalyzed oxidant generation and arachidonic acid products, the release of LTB4 by alveolar macrophages can increase with the eoneentrations of iron complexed to the surface of silica and asbestos (84). Similarly, the eellular release of eytokines postulated to participate in the infiammatory and fibrotic responses ean be associated with exposures to metal-dependent radicals (see Fig. 1). TNF-a produetion by alveolar macrophages after mineral oxide exposure can be inhibited by both the metal chelator deferoxamine and hydroxyl radical scavengers (74). The release of other cytokines pertinent to silica and asbestos exposure ean also be responsive to oxidative stress (85,86). The release of these pertinent mediators after dust exposures is likely to be controlled by oxidant-sensitive promoters such as nuclear factor (NF)-kB (87). After exposure to silica and asbestos, NF-kB can function as a promoter... 

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