Nitroso compound dimers nitro compounds

Ttinitroparaffins can be prepared from 1,1-dinitroparaffins by electrolytic nitration, ie, electrolysis in aqueous caustic sodium nitrate solution (57). Secondary nitroparaffins dimerize on electrolytic oxidation (58) for example, 2-nitropropane yields 2,3-dimethyl-2,3-dinitrobutane, as well as some 2,2-dinitropropane. Addition of sodium nitrate to the anolyte favors formation of the former. The oxidation of salts of i7k-2-nitropropane with either cationic or anionic oxidants generally gives both 2,2-dinitropropane and acetone (59) with ammonium peroxysulfate, for example, these products are formed in 53 and 14% yields, respectively. Ozone oxidation of nitroso groups gives nitro compounds 2-nitroso-2-nitropropane [5275-46-7] (propylpseudonitrole), for example, yields 2,2-dinitropropane (60). 

Although likewise unequivocally dimeric as solids, 2,6-dimethyl- and 2,4,6-trimethylnitrosobenzene (41 and 42) allow for relatively unequivocal thermochemical analysis of both the monomeric and dimeric gases. The desired enthalpies of formation67 of monomeric 41 and 42 are 207.3 12.3 and 140.6 12.5 kJmol-1 respectively. Are these values for the enthalpies of formation of nitrosobenzene derivatives consistent with each other The first comparison considers the difference of the enthalpies of formation of nitroso and nitro compounds, ArNO and ArN02, 547 (Ar NO, NO2) ... 

Irradiation of 1-methyl-2-nitrocyclohexene 200 in benzene in the presence of methyl acrylate showed a dual pathway to give both isoxazoline 201 (54%) and the C-nitroso dimer 202 (22%)118 (equation 96). The isoxazoline 201 arose from an excited-state intramolecular cyclization and scission to give a nitrile N-oxide which is trapped by the acrylate. Concurrently, the photoinduced nitro-nitrite inversion also occurs competitively to give the C-nitroso compound which is isolated as the dimer 202. 

In contrast to a straightforward and predictable decomposition pattern of photolysis with >400 nm light, irradiation of nitrosamides under nitrogen or helium with a Pyrex filter (>280 nm) is complicated by the formation of oxidized products derived from substrate and solvent, as shown in Table I, such as nitrates XXXIII-XXXV and nitro compound XXXVI, at the expense of the yields of C-nitroso compounds (19,20). Subsequently, it is established that secondary photoreactions occur in which the C-nitroso dimer XIX ( max 280-300 nm) is photolysed to give nitrate XXXIII and N-hexylacetamide in a 1 3 ratio (21). The stoichiometry indicates the disproportionation of C-nitroso monomer XVIII to the redox products. The reaction is believed to occur by a primary photodissociation of XVIII to the C-radical and nitric oxide followed by addition of two nitric oxides on XVIII and rearrangement-decomposition as shown below in analogy... 

A number of dihalogenated aromatic amines have been conveniently converted into the corresponding nitroso compounds by room-temperature oxidation with peracetic acid with and without the presence of catalytic amounts of sulfuric acid. Care must be taken to maintain mild reaction conditions to prevent the conversion of the nitroso product into a nitro compound [84]. The example cited here for the preparation of 2,6-dichloronitrosobenzene dimer does afford an excellent yield. 

The nitrosation of aliphatic carbon atoms, particularly of carbon atoms activated by adjacent carbonyl, carboxyl, nitrile, or nitro groups, has been reviewed in great detail [2]. Judging from this review, with few exceptions, nitrosation of active methylene compounds leads to the formation of oximes (unfortunately termed isonitroso compounds in the older literature). The few exceptional cases cited in which true nitroso compounds (or their dimers) were formed involved tertiary carbon atoms in which no hydrogen atoms were available to permit tautomerism to the oxime or involved a reaction which was carried out under neither acidic nor basic conditions. 

Nitro-compounds fRNOj) are isomeric with nitrites, but their electronic structure, excited states and photochemistry are very different. There is no very low-lying (n.jt ) state, and nitroalkanes show n — 3i absorption with a maximum around 275 nm ( —201 mol - cm In cyclohexane solution, nitromethane (CH1NOi) is photoreduced to nitrosomethane(CH,NO, but nitroethane under the same conditions gives rise to a nitroso-dimer derived from the solvent CS.47). The latter process is probably initiated by cleavage of the carbon-nitrogen bond in the nitroalkane. In basic solution (when the nitroalkane is converted to a nitronate anion) irradiation can lead to efficient formation of a hydroxamic acid (S.48), and this reaction most likely proceeds through formation of an intermediate three-mem bered cyclic species. 

Even though most of the synthetic work was directed toward four- and six-electron reduction of nitro groups, voltammetry suggests that other products could result.117 In one of the above examples, the first-formed nitroso compound can form azoxy dimers, which are subsequently reduced to the azo compounds. 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

MCPBA has been regarded as the reagent of choice for the conversion of primary aliphatic amines into the corresponding nitro compounds. The peroxy acid must be used in excess to minimize formation of dimers of the intermediate nitroso compounds, llie yield of nitroalkane is also increased if the reaction is carried out at elevated temperature, since this favors the monomeric rather than the dimeric foim of the intermediate nitrosoalkane and allows it to be oxidized further. For example, cyclohexylamine gave the dimer of nitrosocyclohexane (43%) when oxidized by MCPBA at 23 C, but at 83 C (in boiling 1,2-di-chloroethane) the only product was nitrocyclohexane (86%). 

The jS-nitroso nitro compounds 1 and 2 were prepared as crystalline dimers by reaction of cyclohexene and styrene with pure nitric oxide under pressure. Homospecific and heterospecific dimerization of the initial adducts may occur, however, the X-ray spectrum of the cyclohexene derivative showed the presence of only one rran.r-diastereomer, although other trans- or cis-diastereomers may have been formed. Furthermore, handpicking of the crystal mass of the styrene adduct allows the separation of the clear meso or (R, S ) form and the opaque dl or (R, R ) form, identified by H-NMR spectroscopy. 

The reduction of nitro compounds should initially produce nitroso compounds. This area has not been systematically explored because the nitroso group can be more easily introduced by alternative methods such as direct nitrosation, condensation and oxidative procedures. - In fact, there have been few instances in which nitroso compounds have been isolated as intermediates in reductions of nitro compounds. For example, it was initially believed that w-trifluoromethylnitrobenzene produced the corresponding nitroso compound upon reduction, but subsequently the product was shown to be w-trifluoromethylazox-ybenzene. - Low yields of an intramolecular dimeric, nitroso compound, benzo[c]cinnoline dioxide (1), can be obtained by reducing 2,2 -dinitrobiphenyl with zinc or sodium sulfide (equation I). - ... 

Synthesis o-f transition metal derivative s. In view o-f the -final goal o-f this survey, that is the catalytic deoxygenation o-f nitro compounds by carbon monoxyde, o-f particular interest are the stoichiometric reactions o-f these compounds with metal carbonyls. Carbonyl ligands coordinated to metal atoms in a high oxydation state should be more susceptible to attack by nucleophiles, than those bound to metal in a low oxydation state. However, the reactivity o-f nitro compounds has been studied in practice only with carbonyl complexes o-f metals in zero or less oxydation states. The -first report in this -field is concernded with the reactions o-f Fe(C0>5 with a series o-f aromatic nitro compounds] 56], leading to dimeric iron-nitroso derivatives[23j ... 

The formation of a nitroso complex from the reaction of an organic nitro compound and a metal carbonyl complex was the topic of the first report in this field. It has been reported that by reaction of Fe(CO)5 with a series of aromatic nitro compounds, dimeric iron-nitroso derivatives can be obtained (eq. 15) [50-52] ... 

B, products giving positive Tollen s Reagent tests were obtained. No attempts were made to isolate either 9A or 9B since previous work had indicated that such compounds were subject to decomposition, and bromine oxidation was attempted on the crude reaction mixture. For both systems, as bromine addition was carried out, a transient blue color was noticed and white precipitates appeared in the reaction mixtures. In order to obtain 11A and IIB in purer form, the precipitated crude polymer was subjected to Soxhlet extraction with ethanol. This was followed by azeotropic distillation of benzene over the insoluble products. These two purification steps removed most of the non-polymeric by-products including unreacted or partially reacted nitro compounds as well as water and ethanol. Both llA and IIB showed strong IR absorption at 1200 cm" characteristic of the trans nitroso dimer bond, and a medium sharp absorption... 

The chapter opens with a number of general comments (I, II) and then moves to the section on nitroso compounds (II, B). These latter groups can lead to fairly complex spectra because isomerization (enolization) to oximes can occur (II, B4), and in the case of tertiary and aromatic systems dimerization is possible (II, B5). Nitrosoamines also tend to dimerize to give spectra that are consistent with the above assignments (II, D). Finally, there are a detailed discussions of nitro ( NO2 (III, A, B)) and nitrate (O NOa (III, C)) groups. Here the stretching frequencies are enormously intense and are often the most intense bands in the spectrum. 

The addition of nitrosyl chloride to alkenes is a well-known reaction1 3, nevertheless the mechanistic and stereochemical aspects are still not properly understood. The course of the reaction depends on the nature of the alkene and the experimental conditions. After the initial addition step, which gives a blue or sometimes green 1 1 adduct, three competitive pathways may be followed 1) dimerization of the nitroso group to give a white crystalline compound 2) oxidation of the nitroso group to a nitro group (see Section 7.2.1.8) 3) isomerization to a-chloro oximes. 

Indirect replacement of the a-hydrogen atom of carboxylic esters by the nitroso group is remarkable. This procedure uses ketene 0-alkyl O -silyl acetals (1), generated from carboxylic esters, which are treated with nitric oxide or isopentyl nitrite in the presence of titanium(IV) chloride. In the absence of an a-hydrogen a-nitroso esters (2) are obtained. a-Nitroso esters with an a-hydrogen undergo isomerization to oximes of a-keto esters (3 equation 1). Similarly, silyl enol ethers of aldehydes or ketones can be used instead of the carbonyl compound itself for nitrosation. Thus, treatment of enol ether (4) with nitro-syl chloride gives the a-nitroso aldehyde (5 equation 2), which is quite stable at 0 C, but dimerizes at room temperature. 

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