O Dinitrobenzene

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

Dissolve 200 g. of sodium nitrite in 400 ml. of water in a 2-litre beaker provided with an efficient mechanical stirrer, and add 40 g. of copper powder (either the precipitated powder or copper bronze which has been washed with a little ether). Suspend the fluoborate in about 200 ml. of water and add it slowly to the well-stirred mixture. Add 4-5 ml. of ether from time to time to break the froth. The reaction is complete when all the diazonium compound has been added. Transfer the mixture to a large flask and steam distil until no more solid passes over (about 5 litres of distillate). Filter off" the crystalline solid in the steam distillate and dry upon filter paper in the air this o-dinitrobenzene (very pale yellow crystals) has m.p. 116° (t.c., is practically pure) and weighs 29 g. It may be recrystallised from alcohol the recrystallised solid melts at 116-5°. 

Although potassium fluoride is the preferred nucleophile, tetiabutylam-monium fluoride (TBAF) is successfully used for aromatic fluorodenitration o Fluoronitrobenzene can be obtained in quantitative yield from o-dinitrobenzene in tetra hydrofuran at 25 °C after 1 5 h 7]... 

The action of hydroxylamine and sodium acetate in ethanol upon picryl chloride was stated to give 4,6-dinitrobenzofuroxan, and probably some of this compound was formed, although it was later shownthat much of the original work was faulty. A report that hydroxylamine and 2,4,5-trinitrotoluene give 5-methyl-6-nitro-benzofuroxan has been found to be incorrect. Benzofuroxan has not been prepared by V-oxidation of benzofurazan, and it seems unlikely that this could be achieved, since benzofuroxan itself is oxidizable by powerful reagents to o-dinitrobenzene (Section VI, B). A report of the oxidation by nitric acid of anthraceno[l,2-c]furazan to the furoxan is incorrectlv abstracted. 

Benzofuroxan and 5-methylbenzofuroxan are oxidized by trifluoro-peracetic acid to o-dinitrobenzene and 3,4-dinitrotoluene, respectively. 4-Nitro- and 4,6-dinitrobenzofuroxan are unaffected by this reagent, whereas the 5-chloro and 5-methoxy compounds are destroyed.Milder reagents (performic, peracetic acids) do not oxidize benzofuroxans. ... 

Intermolecular displacements of a nitro group from -dinitrobenzene proceed very rapidly 0 give various subsdtiidon products. o-Dinitrobenzene is as reacdve as -dinitrobenzene, but n-dinitrobenzene is less reacdve. 

The kinetics of formation of phosphonates by reaction of o-dinitrobenzene with phosphites have been examined. The energy of activation for the reaction increases as the nucleophilicity of the phosphite decreases, e.g. ethyl diphenylphosphinite 14kcalmol"S diethyl phenylphosphonite 16 kcalmol S and triethyl phosphite 21kcalmol . An intermediate of the type (61), formed by nucleophilic attack of the phosphite, was proposed. In (61) there is a particularly favourable electrostatic interaction. That p-dinitrobenzene is unreactive, is thought to stem from the fact that this compound cannot form an intermediate with such a stabilizing factor. 

The reaction of p-cyanophenol with o-dinitrobenzene in the presence of KF in DMSO gives the corresponding diaryl ether in 95% yield (Eq. 9.4).7... 

TRINITROBENZENE m-DIBROMOBENZENE m-CHLORONITROBENZENE o-CHLORONITROBENZENE p-CHLORONITROBENZENE tn-D I CHLOROBENZENE o-DICHLOROBENZENE p-DI CHLOROBENZENE m-DIFLUOROBENZENE o-DIFLUOROBENZENE p-DIFLUOROBENZENE m-DI NITROBENZENE o-DINITROBENZENE p-DINITROBENZENE BROMOBENZENE MONOCHLOROBENZENE m-CHLOROPHENOL o-CHLOROPHENOL p-CHLOROPHENOL... 

Dinitrobenzene, see 1,3-Dinitrobenzene m-Dinitrobenzene, see 1,3-Dinitrobenzene o-Dinitrobenzene, see 1,2-Dinitrobenzene p-Dinitrobenzene, see 1,4-Dinitrobenzene... 

To detain an nnpaired electron and facilitate the azocoupling, the o-dinitrobenzene anion-radical was tested in the reaction (Todres et al. 1988). Such an anion-radical yielded an azo-coupled prodnct according to Scheme 1.2 (the nitrogen oxide evolved was detected). The reaction led to a para-snbstitnted prodnct, entirely in accordance with the calculated distribution of spin density in the anion-radical of o-dinitrobenzene (Todres 1990). It was established, by means of labeled-atom experiments and analysis of the gas prodnced, that azo-coupling is accompanied by the conversion of one of the nitro gronps into the hydroxy gronp and the liberation of nitric monoxide. In other... 

When a tetraalkylammonium cation is used as a counterion in solvents of high polarity, such as AN or DME, the alkyl groups of the cation hinder the mutual approach of species with different charges. Ion pairs with the potassium cation are stable. This follows from a comparison of the polarographic behavior of the three isomeric dinitrobenzenes in the same solvent (DMF) using tetraethylammonium or potassium perchlorate as the carrier electrolyte (Todres 1970). The halfwave potentials corresponding to the conversion of p- and m-dinitrobenzenes into anion-radicals are independent of whether tetraethylammonium or potassium counterions are employed. The anion-radical is formed from o-dinitrobenzene at a potential that is less negative by almost 100 mV when... 

When the coordination complex is destroyed, no azo coupling takes place. In this case, only electron transfer products are formed, namely, o-dinitrobenzene, a benzene derivative RCgH from RCgH4N2BF4, gaseous nitrogen, and KBF4. 

Figure 6 Rate constants for electron attachment to solutes in cyclohexane at 295 K. Solutes are 1—CCI4, 2— -dinitrobenzene, 3—benzoquinone, 4—o-dinitrobenzene, 5— nitrobenzene, 6—O2, 7— perfluoromethylcyclohexane, 8—pyrene, 9—anthracene, 10— biphenyl, 11— naphthalene, 12—CO2, 13— -difluorobenzene, 14—ethylbromide. Dotted line indicates calculated diffusion rate. References for rate data [19,108-111] references for electron affinities [112-115].

---