Nitrosobenzene from aniline

In this way nitrosobenzene may be obtained from aniline, as has been shown by Bamberger and Tschimer [220], Nitrosobenzene may then be oxidized to nitrobenzene. 

Phenazine mono-N-oxides have also been prepared from nitrobenzene derivatives. Condensation of nitrobenzene with aniline using dry NaOH at 120-130 °C results in modest yields of phenazine 5-oxide, although the precise mechanism of this reaction is not well understood (57HC(ll)l) with unsymmetrical substrates it is not possible to predict which of the isomeric fV-oxides will be produced. Nitrosobenzene derivatives also function as a source of phenazine mono-fV-oxides thus, if 4-chloronitrosobenzene is treated with sulfuric acid in acetic acid at 20 °C the fV-oxide is formed (Scheme 21). 

In the reaction profile shown in Figure 1 (similar to that shown by Smith et al. (10)) the initial product was azoxybenzene. However this figure is deceptive firstly azoxybenzene may be produced by a non-catalyzed reaction between nitrosobenzene and phenyl hydroxylamine (10), secondly the figure does not show the mass balance. Indeed at 10 min when all nitrosobenzene has been removed from the solution the amount of azoxybenzene formed was 18.6 mmol, equivalent to 37.2 mmol of reacted nitrosobenzene. Therefore, 42.8 mmol of the original 80 mmol of nitrosobenzene (53.5 %) were unaccounted for. It is possible that the missing mass is in the form of phenyl hydroxylamine in solution, which continues to disproportionate to produce aniline and nitrosobenzene and subsequently azoxybenzene and azobenzene. However as we shall subsequently discover this interpretation is unsustainable. 

Let us now turn to some kinetic considerations of NAC reduction. As an example, consider the time courses of nitrobenzene (NB) concentration in 5 mM aqueous hydrogen sulfide (H2S) solution in the absence and presence of natural organic matter (Fig. 14.7). As is evident, although reduction of NB by H2S to nitrosobenzene and further to aniline (Eq. 14-31) is very favorable from a thermodynamic point of view (see Fig. 14.4), it seems to be an extremely slow process. However, when DOM is added to the solution, reduction occurs at an appreciable rate (Fig. 14.7). In order to understand these findings, some general kinetic aspects of redox reactions involving NACs should be recognized. 

It can be seen from this figure that the steady state production of nitrosobenzene is preceded by an induction period, in which aniline is the main product. Further, small amounts of azobenzene and azoxybenzene are formed throughout the reaction. The existence of an autoredox reaction implies that a selectivity of 100% from nitrobenzene to nitrosobenzene is impossible. After the induction period the selectivity of nitrobenzene to nitrosobenzene becomes above 90% of the reduction products. The extent of conversion of nitrobenzene is also time dependent. In the steady state situation about 20% of the nitrobenzene is converted, after an initial conversion of 65%. 

Scheme 9 that both the molybdenum and iron complexes can catalyze the allylic amination of nonfunctionalized alkenes with an ene-like transposition of the double bond, but also that the yield of the allyl amine formed, 113, is moderate to high. It is generally found that higher substituted alkenes tend to give the best yields, and un-symmetrical alkenes (trisubstituted) react with virtually complete regioselectivity, as only one isomer is detected. The byproducts are primarily azoxybenzene and aniline, which arise from condensation of nitrosobenzene with phenyl hydroxylamine and reduction of phenyl hydroxylamine, respectively. 

Q The nitroso group exhibits similar behaviour to a carbonyl group. Predict the products from the reaction of nitrosobenzene with (a) malononilrile (propane-1,3-dinjtrile), (b) hydroxylamine and (c) aniline. Suggest a mechanism for the last reaction. 

Nitrosobenzene (3) can be prepared by oxidation of aniline by H2SO5 (see Section 7.2.2) and by oxidation of phenylhydroxylamine (4) with potassium dichromate. Phenylhydroxylamine is available from nitrobenzene by reduction with zinc dust and aqueous ammonium chloride (Scheme 7.10). 

In a study of rats that received radiolabeled nitrobenzene by gavage, it became bound to the tissues after the first day according to the following indices [mmol/mol Hb/dose (mmol/kg)] blood-229, liver-129, kidney-204, lung-62. By day 7, the same indices were 134, 26.5, 48, 29. After the first day, 50% of the dose (radioactivity) appeared in the urine and 4% in the feces. After the fifth day, 65% of the dose had appeared in the urine and 16% appeared in the feces (Albrecht and Neumann 1985). These studies confirmed the observation of Rickert et al. (1983), that the excretion of nitrobenzene is delayed. The binding indices also indicated that 4 to 5 times as much nitrosobenzene is formed from nitrobenzene as from an equal amount of aniline. 

It can be concluded from the results presented above that reduction of nitrobenzene to nitrosobenzene is occurring via the Mars and van Krevelen mechanism. Reduction to aniline always happens in the first stages of the reaction, but it is not sure by which mechanism this reduction proceeds. In any case, surface hydroxyl groups are the most important hydrogen source. 

When Raney nickel catalysts were used, it was found that the intermediate products of reduction absorbed hydrogen at lower rates than did nitrobenzene. The relative rates of hydrogenation were found to be as shown in Table 5-10 It would therefore appear that nitrosobenzene is not one of the intermediate steps in going from nitrobenzene to aniline. 

---