Dinitrobenzenes, reduction

This compound is polarographically reducible in the whole pH region in a six-electron reaction [348], and the product is supposedly o-phenylenediamine. At a macroelectrode some condensation reactions may be expected to occur in acid solution as side reactions just as in the case of o-dinitrobenzene reduction [349]. 

Another application of diazotization in synthetic strategy is illustrated in the synthesis of 1,3-dibromobenzene (m-dibromobenzene). Direct electrophilic bromination of benzene is not feasible for this purpose after the first bromine has been introduced, the second will attack ortho or para. What is required is a meta-directing substituent that can be transformed eventually into bromine. The nitro group is such a substituent. Double nitration of benzene furnishes 1,3-dinitrobenzene (m-dinitrobenzene). Reduction (Section 16-5) leads to the ben-zenediamine, which is then converted into the dihalo derivative. 

CfiHgNj. Colourless crystals m.p. 63 C, b.p. 2%TC. Turns brown in air. Prepared by a one-stage reduction of m-dinitrobenzene with iron and hydrochloric acid. 

Only the mono-amines are described here. The diamines are more frequently encountered as reduction products of dinitrobenzenes and nitro-anilines, and the chief reactions of the phenylenediamines are therefore given in Section 23, pp. 384-388. 

It is convenient to include under Aromatic Amines the preparation of m-nitroaniline as an example of the selective reduction of one group in a polynitro compound. When wt-dinitrobenzene is allowed to react with sodium polysulphide (or ammonium sulphide) solution, only one of the nitro groups is reduced and m-nitroanUine results. Some sulphur separates, but the main reaction is represented by ... 

In certain cases, alkanolamines function as reduciag agents. For example, monoethanolamine reduces anthraquiaone to anthranols, acetone to 2-propanol, and azobenzene to aniline (17). The reduction reaction depends on the decomposition of the alkan olamine iato ammonia and an aldehyde. Sinulady, diethan olamine converts o-chloronitrobenzene to 2,2 -dichloroazobenzene and y -dinitrobenzene to 3,3 -diamiQoazobenzene. 

These additives can have essentially a reductive character such as the Zn powder or a radical trapping character such as p-dinitrobenzene, triphenylphosphine, p-diaminobenzene, di-tertiobutylphenol or both characters in the case of hydroquinone. 

Some of the reactions in this chapter operate by still other mechanisms, among them an addition-elimination mechanism (see 13-15). A new mechanism has been reported in aromatic chemistry, a reductively activated polar nucleophilic aromatic substitution. The reaction of phenoxide with p-dinitrobenzene in DMF shows radical features that cannot be attributed to a radical anion, and it is not Srn2. The new designation was proposed to account for these results. 

Aromatic nitrocompounds (see Fig. 21) such as nitrobenzene and the dinitrobenzenes diminish the rate of polymerization of styrene without suppressing it altogether and without introducing an induction periodi.e., they are typical retarders. Larger quantities are required to produce significant reductions in the rate, and the retardation persists throughout the polymerization, suggests... 

These concepts were recently applied to an understanding of the electrochemical reduction of the mono and dinitro derivatives of the nonbenzenoid hydrocarbon 24a45. Compound 24b exhibits a single one-electron wave at —1.08 V, while dinitro compound 25 exhibits two one-electron waves at —0.88 and —1.05 V46. This behavior is quite similar to that exhibited by ortfto-dinitrobenzene (21) it appears therefore that 25 is reduced to a dianion in which the quinoidal structure 26 is an important contributor to the resonance hybrid. The quinoidal structure 11 could be produced from 25 even though the... 

Dinitrobenzene is an intermediate employed in chemical syntheses of a large number of compounds used in the dye, explosives and plastics industry. The compound is known to induce methemoglobinemia and to cause testicular toxicity with the Sertoli cell being the major target. Nitro reduction was observed in erythrocytes, in rat Sertoli-germ cell cocultures and in rat testicular subcellular fractions, and it was shown that 3-nitrosonitrobenzene was formed that was considerably more toxic. Testicular toxicity was enhanced when the intracellular thiol levels were reduced by pretreatment with diethylmaleate. In turn, pretreatment with cysteamine or ascorbate reduced the toxicity of 1,3-dinitrobenzene and 3-nitrosonitrobenzene. 

Kurz, L.C. and Erieden, C. (1977). Comparison of the structures of enzymatic and nonenz3fmatic transition states. Reductive desulfonation of 4-X-2,6-dinitrobenzene-sulfonates by reduced nicotinamide adenine dinucleotide. Biochemistry 16, 5207 -5216... 

Titanium ions can also he used as redox catalysts for the indirect cathodic reduction of nitro compounds (417). The electroreduction is carried out in an H20-H2S04/Ti(S04)2-(Pb/Cu) system at 45 80°C under 5 20Am . Nitrobenzene, dinitrobenzene, nitrotoluene, 2,4-dinitrotoluene, 2-nitro-m-xylene, nitro-phenol, 2,4-dinitrophenol, nitrophenetole, o-nitroanisole, 4-nitrochlorotoluene, ni-trobenzenesulfonic acid, and 4,4 -dinitro-stilbene-2,2 -disulfonic acid can all be reduced by this procedure to the corresponding amino compounds (418) in good yields (Scheme 146) [513-516]. Tin... 

Fig. 3 Electrochemical and homogeneous standard free energies of activation for self-exchange in the reduction of aromatic hydrocarbons in iV.A -dimethylformamide as a function of their equivalent hard sphere radius, a. 1, Benzonitrile 2, 4-cyanopyridine 3, o-toluonitrile 4, w-toluonitrile 5, p-toluonitrile 6, phthalonitrile 7, terephthalonitrile 8, nitrobenzene 9, w-dinitrobenzene 10, p-dinitrobenzene 11, w-nitrobenzonitrile 12, dibenzofuran 13, dibenzothiophene 14, p-naphthoquinone 15, anthracene 16, perylene 17, naphthalene 18, tra 5-stilbene. Solid lines denote theoretical predictions. (Adapted from Kojima and Bard, 1975.)...

The replacement of one nitro group in w-dinitrobenzene by a chlorine atom by means of partial reduction and diazotization has been described by Griess.4... 

The reduction to produce azoxy compounds appears to be successful for a wide range of aromatic nitro compounds. The following compounds, however, could not be reduced 1-nitronaphthalene, m-dinitrobenzene, 3,5-dinitroben-zoic acid (although o-, m-, and p-nitrobenzoic acids were reduced smoothly), compounds containing an amino group o-, orp- to a nitro group (except sodium... 

Note No color is produced when an acetonic soln of MNB is treated with aq NaOH(Ref 5) Dinitrobenzenes. Of these, only the m-isomer is of importance in the expls industry. For its detection and estimation, there may be used the reduction method proposed by Smyth et al(Refs 4 5). In this method the m-DNB is reduced by addg... 

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