Dinitrobenzene anions

Another example is the m-dinitrobenzene anion radical in aqueous solution,11,12 where the effect is due to asymmetric solvation (one nitro group solvated, the other not), an effect very similar to that with dinitrodurene anions. In this case the mean lifetime of one solvation state was 0.8 ps at 291 K and 4.5 ps at 282 K. Still more examples are mentioned in the reviews by Atkins in the early 1970s.13... 

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... 

The electrochemical behavior of l-fluoro-2,4-dinitrobenzene, l-chloro-2,4-dinitrobenzene, and l-bromo-2,4-dinitrobenzene in DMF was described (Gallardo et al. 2000) as follows. The 1-fluoro-2,4-dinitrobenzene anion-radical dimerizes before cleavage, whereas l-chloro-2,4-dinitrobenzene... 

Figure 21, The n-dependence of the relative rate constant for the formation of 1, 4-dinitrobenzene anions (pDNB ) in collisions of pDNB with Xe(nf) atoms.

Studies of micellar catalysis of himolecular reactions of uncharged substrates have not been frequent" ". Dougherty and Berg performed a detailed analysis of the kinetics of the reaction of 1-fluoro-2,4-dinitrobenzene with aniline in the presence of anionic and nonionic surfactants. Micelles induce increases in the apparent rate constant of this reaction. In contrast, the second-order rate constant for reaction in the micellar pseudophase was observed to be roughly equal to, or even lower than the rate constant in water. 

Another example of the analogy between pyrazole and chlorine is provided by the alkaline cleavage of l-(2,4-dinitrophenyl)pyrazoles. As occurs with l-chloro-2,4-dinitrobenzene, the phenyl substituent bond is broken with concomitant formation of 2,4-dinitrophenol and chlorine or pyrazole anions, respectively (66AHC(6)347). Heterocyclization of iV-arylpyrazoles involving a nitrene has already been discussed (Section 4.04.2.1.8(i)). Another example, related to the Pschorr reaction, is the photochemical cyclization of (515) to (516) (80CJC1880). An unusual transfer of chlorine to the side-chain of a pyrazole derivative was observed when the amine (517 X = H, Y = NH2) was diazotized in hydrochloric acid and subsequently treated with copper powder (72TL3637). The product (517 X = Cl, Y = H) was isolated. 

Perfluoroalkyl carbanions, generated by reversible nucleophilic addition of a fluoride anion to fluoroalkenes, react with dry benzenediazonium chloride in dimethyl formamide, giving phenylazoperfluoroalkanes in 41-53% yield (Dyatkin et al., 1972). The dianion obtained from 1,2-dinitrobenzene with dipotassium cyclo-octatetraenide reacts in a complex way with arenediazonium salts, forming 4-aryl-azo-2-nitrophenol in 46-58% yield (Todres et al., 1988). 

Normally, the radical anion could be the starting point for a competitive process leading also to the same arylated nucleophile but the presence of radical scavengers, such as dinitrobenzene or ditertiobutylphenol would inhibit this secondary way of arylation, increasing the overall yield of arylation. 

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. 

Synthetic pyrethroids with a-cyano ester group react with sodium hydroxide to yield hydrogen cyanide, which reacts with 4-nitrobenzaldehyde and 1,2-dinitrobenzene to yield a pink-colored derivative (o-quinonoid di-anion) according to the following scheme ... 

The regioselective cross-coupling between anions of bromomalonate esters orbromoacetate esters and m-dinitrobenzene proceeds in the presence of copper fert-butoxide to give the 2-substituted product. Without the copper salt, the 4-substituted isomer is the only product (Eq. 9.35).62... 

As an extension of the intermolecular self-exchange described above, the solvent-induced intramolecular electron exchange kinetics in radical anions of 1,3-dinitrobenzene [47] and benzene 1,3-dicarbaldehyde [48] have been studied by several authors (Freed and Fraenkel, 1964 Grampp et al., 1989, 1990b Shohoji et al, 1987). The advantage of [47] and [48] is their structural simplicity and their high stability, which allows measurements even in protic... 

The work reported here is the last experimental study of the Keele Polymer Group which came to an end in 1985. The senior author believes that he has achieved one of his principal chemical objectives, to determine some credible kp values and to discover the optimum conditions. He hopes that others will adopt the use of highly polar solvents and will explore a wide temperature range. For low temperatures, the eutectic mixtures of PhN02 with one of the nitronaphthalenes or dinitrobenzenes will be needed. Another useful, highly polar, solvent is S02. The nitroalkanes should be avoided. The initiator of choice should be an aroyl salt of a stable anion, and it is clear that the ideal such salt has not yet been found, but useful guidelines for finding improved initiators (in terms of speed of reaction, shelf-life and solubility) are available [21]. 

SjvAr reactions of nitroaromatics such as l-chloro-2,4-dinitrobenzene and 2,4,6-trinitroanisole with amines are accelerated in micelles or microemulsions49. As with anionic nucleophiles, the rate enhancement is mainly the effect of a high local concentration of both reactants18,31. 

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... 

It should be emphasized that reactions conducted in traditional ways under inert gaseous atmosphere may sometimes fail. Oxygen accelerates the reactions involving strong acceptor substrates. This is similar to a promoting effect of active organic oxidizers of the dinitrobenzene type. The first example of such catalytic reactions was described almost half a century ago (Russell 1954). A carb-anion (R ) reacts with O2 according to the mechanism of catalysis with a one-electron transfer ... 

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