Scavengers iron-base

When the iron-based catalyst 66 was used, a high level of enantiomeric excess in the cycloadditions between cyclopentadiene (18) and a,/i-unsaturated aldehydes [65] was observed. The cycloadditions were carried out in the presence of 2,6-di-t-butylpyridine (Scheme 3.15) which was added to scavenge residual acid impurities. 

The SulfaTreat process also uses an iron-based scavenger for trace H2S removal. It has the advantage over the traditional iron sponge process of being non-pyrophoric. 

The only iron-based chemicals currently used as scavengers in drilling fluids are the iron oxides, which are insoluble in both water and mud. Reaction mechanisms between iron oxides and soluble sulfides that cause the formation of various iron-sulfur compounds may involve changes in oxidation state, precipitations, or combinations of both. Transformation of iron-sulfide crystalline structure with time also may occur. Chemical literature points out system variables that control reaction... 

Six iron-sulfur minerals are stable enough to exist in nature all contain the ferrous (Fe +) form of iron. Those minerals with iron-to-sulfur ratios of 1 1 (FeS) are mackinawite and pyrrhotite. Those with iron-to-sulfur ratios of 3 4 0 0384) are greigite and smythite. All the iron sulfides with ratios of 1 1 and 3 4 are soluble in mild acids with formation of H2S. Those minerals with iron-to-sulfur ratios of 1 2 (FeSj) are pyrite and marcasite. Pyrite and marcasite are distinguished from the other four iron sulfides by their insolubility in concentrated HCl. Pyrite is highly pH- and temperature-stable. Due to this, it is found often in nature. This inertness also makes pyrite a desirable reaction product for sulfide removal using an iron-based scavenger. Various iron sulfides can be formed chemically from iron compounds reacting with soluble sulfides at ambient conditions in aqueous systems. The specific reaction conditions control both the products formed and the rate of reaction. 

G. Deka, H. Deka and N. Karak, Free radical scavenging magnetic iron-based nano-particles in hyperbranched and hnear polymer matrices , J Macromol Polym Sci PAC, 2009, 46,1128-35. 

Iron-based O2 scavenger Sachets Improved stability of hard cheese 54... 

Flash photolysis techniques were unsuitable for measuring the slow off reactions for the iron(II) model complexes such as Fen(TPPS)(NO), since the experimental uncertainties in the extrapolated intercepts of kohs vs. [NO] plots were larger than the values of the intercepts themselves. When trapping methods were used to evaluate NO labilization from FeII(TPPS)(NO), k(,n values were found to be quite small but were sensitive to the nature of the trapping agents used. Lewis bases that could coordinate the metal center appeared to accelerate NO loss. More reliable estimates for the uncatalyzed off reaction were obtained by using Ru(edta)- as an NO scavenger, and the koS values listed in Table I were obtained in this manner (21c). The small kQ values found for Fe(II) models are consistent with the trend observed for the ferro-heme proteins discussed above. 

In cases where metals or metal ions can contaminate the products, reaction vessels fabricated from inert polymeric materials restrict that possibility. A significant example involved the reaction of maltol with aqueous methylamine to give l,2-dimethyl-3-hydroxypyrid-4-one. The product is a metal chelator employed for the oral treatment of iron overload. Consequently, it is an excellent metal scavenger but must be produced under stringent conditions that preclude metal complexation. Literature conditions involved heating maltol in aqueous methylamine at reflux for 6 h, the product was obtained in 50% yield, but required decolourisation with charcoal135. With the CMR, the optimal reaction time was 1.3 min, and the effluent was immediately diluted with acetone and the near colourless product crystallised from this solvent in 65% yield (Scheme 9.18). A microwave-based batch-wise preparation of 3-hydroxy-2-methylpyrid-4-one from maltol and aqueous ammonia was also developed. 

The third system is based on the scavenger formate. The dioxo-carbonate(l—) radical formed, CO) , is a strongly reducing radical, E CC /CO] ) = —1.8 V [99]. When generated from the Fenton reaction it is expected to reduce the metal and no absorbance change should result. However, we observed an intermediate with absorption maxima near 300 and 410 nm that we ascribed to a compound with iron-carbon a-bonds [2,96,123], similar to those investigated by Cohen and Meyerstein [130] ... 

The efficiency of freshly precipitated iron hydroxide in scavenging plutonium and other actinides from aqueous waste solutions is well known. Processes based on two or more cycles of iron hydroxide precipitation have long been used successfully at the U. S. Department of Energy Rocky Flats and Los Alamos sites to effectively decontaminate actinide-containing waste solutions generated at those sites. (ll+,15.,16)... 

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