Aromatic compound-oxidizing iron reducers

Some reactions of 2,2 -bipyridine /V-oxides have been reported. The l,T-dioxide is nitrated readily to 4,4 -dinitro-2,2 -bipyridine 1,T-dioxide. ° ° °" 2,2 -Bipyridine 1-oxide is also nitrated in the 4 position. The nitro groups in 4,4 -dinitro-2,2 -bipyridine l,T-dioxide are reactive, being replaced by chlorine with concentrated hydrochloric acid," by bromine with acetyl bromide, by hydroxyl with dilute sulfuric acid, and by alkoxy groups with sodium alkoxides. Some of the dialkoxy derivatives are useful catalysts for the oxidation of aromatic compounds. The dinitro dioxide is deoxygenated to 4,4 -dinitro-2,2 -bipyridine with phosphorus trichloride in chloroform, and other substituted l,T-dioxides behave similarly, but with phosphorus trichloride alone, 4,4 -dichloro-2,2 -bipyridine results. The dinitro dioxide is reduced by iron powder in acetic acid to 4,4 -diamino-2,2 -bipyridine, whereas 4,4 -dichloro-2,2 -bipyridine l,T-dioxide is converted to its 4,4 -diamino analogs with amines. Related reactions have been described. ... 

Reduction of nitro aromatic compounds often appears to be a two-step process, in which a mediator is required for facile transfer of electrons from a bulk reductant to the contaminant. A well documented example is the coupling of organic matter oxidation by iron reducing bacteria to "abiotic" nitro reduction by biogenic Fe(II) that is adsorbed to mineral surfaces in a column containing aquifer material (36, 39, 76). 

Perfluoroaromatic compounds can be obtained by reductive aromatization of readily accessible perfluorocycloaliphatic precursors [73]. Defluorination can be accomplished by contact with hot (500 °C) iron or iron oxide. After reducing the per-fluoroaliphatic compound the metal surface can be regenerated by passage of hydrogen gas. This method has been scaled up to a continuous flow process for industrial synthesis of a variety of perfluorinated aromatic compounds (Scheme 2.27). 

This prediction has been realized. Various aromatic nitro compounds have been reduced to the corresponding amines by treatment at 25 °C in aqueous solution of glyme containing catalytic quantities of Fe(CO)5 and large amounts of triethylamine under a pressure of 1700 psi of CO (18). To observe catalysis, however, it was necessary to maintain the concentration of the oxidant, i.e., the nitrobenzene, low at all times. If this were not done, then rapid loss of the CO ligands occurred (Reaction 9) and irreversible formation of iron oxides (Reaction 10) resulted. The concentration of the oxidant was maintained low inside the reactor vessel simply by pumping in the nitrobenzene over a... 

Varma and his coworkers have described a simple and eflRcient procedure wherein aromatic nitro compounds are readily reduced to the corresponding amino compounds in good yields with hydrazine hydrate supported on alumina in the presence of iron(III) chloride (FeCls 6H2O), Fe(III) hydroxide, or Fe(III) oxides (Scheme 8.60) [159]. 

Iron-reducing bacteria, Geobacter, was shown to obtain energy from the oxidation of aromatic organic compounds, including toluene, phenol, p-cresol, benzoate, and others (Lovley, 1991). 

A-Amine oxides can be reduced (deoxygenated) to tertiary amines. Such a reaction is very desirable, especially in aromatic nitrogen-containing heterocycles where conversion to amine oxides makes possible electrophilic substitution of the aromatic rings in different positions than it occurs in the parent heterocyclic compounds. The reduction is very easy and is accomplished by catalytic hydrogenation over palladium [736, 737], by borane [738], by iron in... 

The iron sulfide complex (10) resembles the active sites of oxidized rubredoxins nonheme iron-sulfur proteins. The complex catalyzes the reductions of aromatic nitro compounds to A -arylhydroxylamines by thiol (equation 11 ). The method offers a facile, high yield approach to N-arylhydroxylamines. For example, p-dinitrobenzene was reduced to p-nitrophenylhydroxylamine in 92% yield. 

For the reduction of nitroarenes to aminoarenes by the catalytic hydrazine H-transfer reduction method, the classical hydrogenation catalysts Ni, Pd and Pt are most commonly used [1] [2]. In a more extended study [3] we were able to confirm previously reported observations [4] that these reductions can also be catalysed by modified iron oxides hydroxides. This method for the production of many aromatic amines offers several advantages compared to the conventional processes still employed in industry, such as the environmentally imfavourable Bechamp [5] and Zinin reductions [6]. It is an outstanding feature of the novel reduction method presented here that further reducible substituents in nitroazo compounds, such as... 

---