Aniline nitrobenzene reduction with iron

The aniline processes that are currently in use include (1) hydrogenation of nitrobenzene, (2) nitrobenzene reduction with iron filings, and (3)... 

Nitrobenzene Reduction with Iron Filings. The older Bechamp method for iron oxide pigment production gives aniline as a coproduct and is operated by Bayer in West Virginia. Nitrobenzene is reduced by reaction with iron filings in the presence of a hydrochloric acid catalyst. The iron is oxidized to the ferrous or ferric state and the coproduct aniline is separated. The yield is 90 to 95 percent of theoretical. The reactions are represented as follows.138... 

On reduction, with iron and acetic acid, nitrobenzene yields aniline. 

Aniline may be made (I) hy Ihe reduction, with iron or tin in HOI, of nitrobenzene, and (2) by the amination of chlorobenzene by healing with ammonia to a high temperature corresponding to a pressure of over 200 atmospheres in the presence of a catalyst (a mixture of cuprous chloride and oxide). Aniline is the end-point of reduction of most mono-nitrogen substituted benzene nuclei, as nitrosobenzene, beta-phenylhydroxylamine. azoxybenzene, azobenzene, hydrazobenzene. Aniline is detected by the violet coloration produced by a small amount of sodium hypochlorite. 

The traditional treatment of nitrobenzene (1) with iron and acid, called Bechamp reduction, was employed almost exclusively in the production of aniline (2) and many aromatic amines until the 1960s1,2 (Scheme 1). The reduction is straightforward, and can also be achieved by catalytic hydrogenation, sodium sulfide reduction and zinc reduction with caustic soda. Nitrotoluenes and nitroxylenes are hydrogenated under pressure over a nickel catalyst supported on kieselguhr. The sulfide reduction is useful in selective reduction, such as of m-dinitrobenzene to m-nitroaniline. 

In the reduction of nitro compounds to amines, several of the iatermediate species are stable and under the right conditions, it is possible to stop the reduction at these iatermediate stages and isolate the products (see Figure 1, where R = CgH ). Nitrosoben2ene [586-96-9] C H NO, can be obtained by electrochemical reduction of nitrobenzene [98-95-3]. Phenylhydroxylamine, C H NHOH, is obtained when nitrobenzene reacts with ziac dust and calcium chloride ia an alcohoHc solution. When a similar reaction is carried out with iron or ziac ia an acidic solution, aniline is the reduction product. Hydrazobenzene [122-66-7] formed when nitrobenzene reacts with ziac dust ia an alkaline solution. Azoxybenzene [495-48-7], C22H2QN2O, is... 

Nitroaromatic compounds (NACs) are one of the widespread contaminants in the environments. Sources of NACs are numerous they originate from insecticides, herbicides, explosives, pharmaceuticals, feedstock, and chemicals for dyes (Agrawal and Tratnyek, 1996). Under anaerobic conditions, the dominant action is nitro reduction by zero-valent iron to the amine. Other pathways do exist, such as the formation of azo and azoxy compounds, which is followed by the reduction of azo compounds to form amines. Also, in addition to the possibility of azo and azoxy compounds, phenylhydrox-ylamine may be an additional intermediate (Agrawal and Tratnyek, 1996). Nitrobenzene reduction forms the amine aniline. Known for its corrosion inhibition properties, aniline cannot be further reduced by iron. Additionally, it interferes with the mass transport of the contaminant to the surface of the iron. The overall reaction is as follows ... 

The reduction of nitrobenzene to aniline by CO and Hj is more effectively carried out with ruthenium than with iron or osmium . 

Aniline a-n l-on [Gr aniliny fr. Anil indigo, fr. FP, fr. Arabic an-nil the indigo plant, fr. Sanskrit fr. mil indigo, fr. feminine of ntla dark blue] (1850) (phenylamine, amino-benzene) n. C6H5NH2. A colorless, oily liquid made by the reduction of nitrobenzene with iron chips and an acid catalyst. It is used in the production of aniline-formaldehyde resins and certain catalysts and antioxidants. 

For the preparation of nitrocymene a method developed in the Colour Laboratory and described in the Jour, of Ind. and Eng. Chem. in 1918, p. 453, was used. The nitro group enters in the ortho position with respect to the methyl group. The reduction of this compound to aminocymene or cymidine was accomplished by means of iron powder and hydrochloric acid in exactly the same way as nitrobenzene is reduced to aniline. 

This reduction step can be readily observed at a mercury electrode in an aprotic solvent or even in aqueous medium at an electrode covered with a suitable surfactant. However, in the absence of a surface-active substance, nitrobenzene is reduced in aqueous media in a four-electron wave, as the first step (Eq. 5.9.3) is followed by fast electrochemical and chemical reactions yielding phenylhydroxylamine. At even more negative potentials phenylhydroxylamine is further reduced to aniline. The same process occurs at lead and zinc electrodes, where phenylhydroxylamine can even be oxidized to yield nitrobenzene again. At electrodes such as platinum, nickel or iron, where chemisorption bonds can be formed with the products of the... 

Aniline is an important derivative of benzene that can be made in two steps by nitration to nitrobenzene and either catalytic hydrogenation or acidic metal reduction to aniline. Both steps occur in excellent yield. Almost all nitrobenzene manufactured (97%) is directly converted into aniline. The nitration of benzene with mixed acids is an example of an electrophilic aromatic substitution involving the nitronium ion as the attacking species. The hydrogenation of nitrobenzene has replaced the iron-... 

The first experiments which were carried out in the author s laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes (4) to anilines (5) by triiron dodecacarbonyl. Such a conversion was reported to occur in benzene containing methanol at reflux for 10-17 h, with the hydridoundecacarbonyltriferrate anion as the likely key intermediate (16). It was our expectation that the trinuclear iron hydride should be generated by phase-transfer catalysis and if so, effect reduction of nitro compounds (4) under exceedingly mild conditions. Indeed this was the case, as illustrated by the results shown in Table I (17). Not only is the reaction complete in 2 h or less using sodium hydroxide as the aqueous phase, benzene as the organic phase, and benzyltrieth-ylammonium chloride as the phase-transfer catalyst, but it occurs at room temperature and requires less metal carbonyl than when the reaction was... 

The [TPPFeCl] -NaBITi system in diglyme has been shown to perform remarkably efficiently as a catalyst for the reduction of nitrobenzenes to anilines. Although both TPPCo and TPPMnCl also catalyze the reduction of p-chloronitrobenzene to jo-chloroaniline, their catalytic activities are much lower thanthatofTPPFeCl. Anothertype of reduction catalyst, in this case of dioxygen to water, begins with carbon-supported chloroiron(ni) tetramethoxyphenylporphyrin, which is then heat-treated at 900 °C for one h." This causes decomposition of the porphyrin to produce metallic, carbidic and oxidic iron, as detected by Mossbauer spectroscopy. The active... 

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