Nitrosobenzene, from

Examples (a) Phenylhydroxylamine from Nitrobenzene1 (b) Nitrosobenzene from Phenylhydroxylamine... 

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). 

The replacement of rhodium from a wide range of rhodacycles to form condensed furans, thiophenes, selenophenes, tellurophenes and pyrroles has been widely explored and a range of examples is shown in Scheme 97. The rhodacycles are readily generated from the appropriate dialkyne and tris(triphenylphosphine)rhodium chloride. Replacement of the rhodium by sulfur, selenium or tellurium is effected by direct treatment with the element, replacement by oxygen using m-chloroperbenzoic acid and by nitrogen using nitrosobenzene. 

Nitrosobenzene [586-96-9] M 107.1, m 67.5-68 , b 57-59 /18mm. Steam distd, then cryst from a small volume of EtOH with cooling below 0°, dried over CaCl2 in a dessicator at atm pressure, and stored under N2 at 0°. Alternatively it can be distd onto a cold finger cooled with brine at —10 in a vac at 17mm (water pump), while heating in a water bath at 65-70° [Robertson and Vaughan J Chem Educ 27 605 1950]. 

Structure 12 may need to be revised, however, since a recent X-ray crystallographic analysis on the corresponding [4 + 2] cycloadduct 13 from ethyl 1//-azepine-1-carboxylate (1) with ethyl 4-nitrosobenzoate reveals the opposite regiochemistry to that proposed for the adduct with nitrosobenzene.297 The [6 + 2] adduct is also formed, in this case in 41 % yield (mp 106-107 C). 

Note Trimethylammonio or pyridinio groups can be displaced from quinoxaline by cyanide ion to afford quinoxalinecarbonitriles or, with nitrosobenzene, to give a nitrone. 

A similar nitrene intermediate can also be postulated in the mechanism of nitrosobenzene hydrogenation. Indeed a standard way of producing Ph-N is from the reaction of Ph-NO with PPhs (17). In the hydrogenation of nitrosobenzene the principal product in the early stages is azoxybenzene [7, 18]. It was suggested that azoxybenzene was formed by the following sequence ... 

Note that the nitrene now allows a common intermediate that can be hydrogenated to anihne from both nitrobenzene and nitrosobenzene. It is also interesting to speculate on another route to form a nitrene on the surface. Phenyl hydroxylamine is a known intermediate whose concentration in solution is highly dependent upon reaction condihons. On adsorption of phenyl hydroxylamine one can write the following ... 

The same corynoline analog (214) was obtained more conveniently through photolysis in the presence of nitrosobenzene. Addition of nitrosobenzene to 208 from the opposite side of the methyl group resulted in the B/C-trans adduct 215. Reduction of 215 with sodium borohydride followed by acidic treatment gave the B/C-cis product 217 via 216. Hydroxylation of 217 with performic acid and hydrogenolysis of the diol 218 completed the synthesis of 214 (126). 

A direct synthesis of the thiophene nucleus has been achieved by allowing air-stable cobaltacyclopentadiene complexes (66) to react with sulfur the organometallic complexes are prepared in variable yields in a stepwise fashion from f75-cyclopentadienyIbis(triphenylphosphine)cobalt (65) (Scheme 82) 147,148 Reactions of the complexes 66 with selenium and nitrosobenzene give rise to selenophenes and pyrroles, respectively. 

This type of method has been used to prepare l,2,4-thiadiazolo[2,3- ]pyridine derivatives. The oxidative hetero-cyclization is exemplified by the formation of compound 86 from thioacetamide 85 using nitrosobenzene (Equation 24) <2004S2975>. 

The reaction in Eq. (15) is under the control of C-6-PDH, that in Eq. (16) is catalyzed by MHbR, while that in reaction (17) is non-enzymatic. It is remarkable that nitrosobenzene is reduced enzymatically to phenylhydroxylamine which oxidizes Hb to MHb and is, by this, reoxidized to nitrosobenzene (L5) the latter substance acts catalyti-cally and not stoichiometrically when forming MHb from Hb by the fact of its regeneration during reaction (17). 

Nitrosamines, 2 449-451 Al-Nitrosamines, 15 531 Nitrosobenzene, Diels-Alder adduct from cyclopentadiene, 8 222t Al-Nitroso compounds, ascorbic acid and, 25 770... 

Apart from rare exceptions, the only nitroso-compounds known are those in which the NO-group is united to a tertiary carbon atom, as in nitrosobenzene. Nitrosoisobutane (H3C)3 C.NO, for example, is a representative from the aliphatic series. 

In this way mixed (asymmetrical) azo-compounds can conveniently be prepared in good yield. Prepare p-methylazobenzene, for example, from nitrosobenzene and p-toluidine according to the procedure given above. 

Experiment.—Azoxybenzenefromphenylhydroxylamine and nitrosobenzene.-—Phenylhydroxylamine (1 g.) is added to a solution of 1 g. of nitrosobenzene in 10 c.c. of alcohol. The mixture is shaken while a few drops of concentrated potassium hydroxide solution (1 1) are added, and is then warmed on the water bath for a few minutes. The yellowish-red solution thus formed deposits yellow crystals of the reaction-product when cooled and rubbed with a glass rod. Since azoxybenzene melts at 36°, it has a great tendency to separate from a supersaturated solution in the form of an oil. By recrystallisation from a little alcohol or from petrol ether (retain a few crystals for inoculation) the compound is obtained as a pale yellow or almost colourless solid. 

Thus the joining of the two molecules by nitrogen takes place when azoxybenzene is formed, and the experiment described on p. 182 shows quite definitely that this substance is produced with extraordinary ease from phenylhydroxylamine and nitrosobenzene in the presence of alkali, that is to say, under the conditions which prevail during the production of the whole series. Nitrosobenzene is the first stage, but cannot be isolated, for in the course of the reaction it is trapped by the phenylhydroxylamine as soon as it is formed. 

The PE spectrum of nitrosobenzene has been investigated by Rabalais and Colton129 and by Green and coworkers128. Unfortunately, the published IP values are considerably at variance. From the characteristic IPs of C-nitroso compounds only IP(n ) = 8.51 eV could be assigned as the first IP. IP2 and IP3 were identified as ionizations of electrons from the benzene MOs ni and 7r3 (Table 13). 

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