Iron reductive transformation

Schwarzenbach et al. (1990) have shown that reductive transformations of a series of monosubstituted nitrobenzenes and nitrophenols in aqueous solutions containing reduced sulfur species occur readily in presence of small concentrations of an iron prophyrin as an electron transfer catalyst. 

Klupinski et al. (2004) conclude that the reduction of nitroaromatic compounds is a surface-mediated process and suggest that, with lack of an iron mineral, reductive transformation induced only by Fe(II) does not occur. However, when C Cl NO degradation was investigated in reaction media containing Fe(II) with no mineral phase added, a slow reductive transformation of the contaminant was observed. Because the loss of C Cl NO in this case was not described by a first-order kinetic model, as in the case of high concentration of Fe(II), but better by a zero-order kinetic description, Klupinski et al. (2004) suggest that degradation in these systems in fact is a surface-mediated reaction. They note that, in the reaction system, trace amounts of oxidize Fe(II), which form in situ suspended iron oxide... 

Weber, E.J., Iron-mediated reductive transformations investigation of reaction mechanism, Environ. Sci. Technol., 30(2), 716-719, 1996. 

Alien-King, R.M., R.M. Halket, and D.R. Burris. 1997. Reductive transformation and sorption of cis- and trans-l,2-dichloroethene in a metallic iron-water system. Environ. Toxicol. Chem. 16, 424-429. 

Weber, E. J. 1996. Iron-mediated reductive transformations Investigation of reaction mechanism. Environmental Science and Technology 30 716. 

In organic compounds, iron is often attached to organic ligands by chelation and, thereby, it can undergo oxidation-reduction transformations that are utilized in electron-transport processes. Cytochromes in electron-transport chains contain chelated iron that undergoes such redox transformations. 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

Reductive Transformation of Halogenated Aliphatic Pollutants by Iron Sulfide... 

Studies in the last decade show that iron sulfide minerals are very reactive in the reductive transformation of chlorinated aliphatic pollutants. These minerals, present in sulfate-reducing anaerobic environments, likely contribute to in-sUu transformation of chlorinated aliphatic pollutants and have potential application in remediation technologies. Solution pH, the presence of organic co-solutes with functional groups representative of natural organic matter, and the thermodynamic or molecular properties of the halogenated aliphatic pollutant all influence the rates and/or products of pollutant transformation. 

This chapter reviews the literature to date on the reductive transformation of halogenated aliphatic pollutants, particularly chlorinated aliphatics, by iron sulfide minerals. 

Numerous reductive transformations of nitroaromatic compounds have been described in the literature (Preu6 and Rieger, this volume). These include gratuitous microbial reactions or chemical reductions by reducing agents in the medium. Thus, in iron-reducing cultures, 4-chloronitrobenzene was rapidly converted into 4-chloroaniline (17). These gratuitous reductions proceed via nitroso and hydroxylamino intermediates and are favored under microaerophilic and even more under anaerobic conditions. 

Observations of smooth spalls in iron provided an early, dramatic demonstration of the importance of release wave behaviors. In 1956, Dally [61E01] reported the existence of remarkably smooth fracture surfaces in explosively compressed steel. The existence of these smooth spalls was a sensitive function of the sample thickness. Analysis and experiments by Erkman [61E01] confirmed that the smooth spalls were associated with interaction of release-wave shocks and shocks from reduction of pressure at free surfaces. These release shocks are a consequence of differences in compressibility at pressures just below and just above the 13 GPa transformation. 

Sometimes the metal may be transformed into a different oxidation state thus copper(II) may be reduced in acid solution by hydroxylamine or ascorbic acid. After rendering ammoniacal, nickel or cobalt can be titrated using, for example, murexide as indicator without interference from the copper, which is now present as Cu(I). Iron(III) can often be similarly masked by reduction with ascorbic acid. 

The chemistry of indium metal is the subject of current investigation, especially since the reactions induced by it can be performed in aqueous solution.15 The selective reductions of ethyl 4-nitrobenzoate (entry 1), 2-nitrobenzyl alcohol (entry 2), l-bromo-4-nitrobenzene (entry 3), 4-nitrocinnamyl alcohol (entry 4), 4-nitrobenzonitrile (entry 5), 4-nitrobenzamide (entry 6), 4-nitroanisole (entry 7), and 2-nitrofluorenone (entry 8) with indium metal in the presence of ammonium chloride using aqueous ethanol were performed and the corresponding amines were produced in good yield. These results indicate a useful selectivity in the reduction procedure. For example, ester, nitrile, bromo, amide, benzylic ketone, benzylic alcohol, aromatic ether, and unsaturated bonds remained unaffected during this transformation. Many of the previous methods produce a mixture of compounds. Other metals like zinc, tin, and iron usually require acid-catalysts for the activation process, with resultant problems of waste disposal. 

This XPS investigation of small iron Fischer-Tropsch catalysts before and after the pretreatment and exposure to synthesis gas has yielded the following information. Relatively mild reduction conditions (350 C, 2 atm, Hg) are sufficient to totally reduce surface oxide on iron to metallic iron. Upon exposure to synthesis gas, the metallic iron surface is converted to iron carbide. During this transformation, the catalytic response of the material increases and finally reaches steady state after the surface is fully carbided. The addition of a potassium promoter appears to accelerate the carbidation of the material and steady state reactivity is achieved somewhat earlier. In addition, the potassium promoter causes a build up on carbonaceous material on the surface of the catalysts which is best characterized as polymethylene. 

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