Nitrosoalkanes, dimerization

Certain olefins have been converted into l-chloro-2-nitrosoalkane dimers on treatment with nitrosyl chloride (Eq. 3). Terminal olefins appear to be active only if they are not allylic in nature. The addition of nitrosyl chloride to norbornene is of particular interest, and details are presented in the body of... 

The naming of monomeric nitroso compounds is generally quite straightforward. In this discussion a dimer is simply indicated as nitrosoalkane dimer or as nitrosoarene dimer if reasonable evidence for the isolation of the dimer is at hand. In the works of Muller and Metzger ([14], etc.) terms such as bis(nitrosoalkane) are used to indicate the dimers. 

Much of the pioneering research on nitrosoalkane dimers is based on reactions involving the formation of free radicals. Most of the reactions are of little value from the preparative standpoint, either because a highly specialized apparatus (e.g., photolysis equipment, high-vacuum trains, even a Van de Graaff generator) is used or because complex mixtures of products are produced. However, this work is of such importance in the historical development of aliphatic nitroso chemistry that it merits a brief review here rather than relegation to Section 5. 

The reaction of nitroalkanes and dinitroalkanes with sodium hydrogen telluride gives nitrosoalkane dimers and olefins, respectively.96 The reduction of other nitrogenated species such as hydroxylamines, azides, nitroso, azo, and azoxy compounds can also be performed by using tellurium reagents.6,11,12... 

Nitroalkanes can be converted to carbonyl compounds in acceptable yields using vanadium(ii) chloride in aqueous dimethylformamide. Treatment of nitroalkanes with acylcarbonylferrate(o) gives a new synthetic route to amides. JViV -Disub-stituted ureas have been prepared, by the same workers, from nitroalkanes (and arenes), bromomagnesium alkylamides, and pentacarbonyliron. The catalytic hydrogenation of nitrosoalkane dimers is a useful route to symmetrical azoxy-alkanes. ... 

Like azo compounds, aromatic aliphatic or mixed azoxy compounds, represented by the general formula R-N+(-0 )=N-R (R, R = alkyl or aryl), exist in E- and Z-forms. Nitrosoalkane dimers, represented by... 

Many nitrosoalkanes and nitrosoarenes exist as dimers at room temperature. In 1976, Gowenlock and Trotman carried out a unique investigation on the isolation of E- and Z-isomers of the nitrosoalkane dimer." They prepared two isomers, A and B, of dimeric nitrosomethane generated by the photolysis and pyrol) is of t-butyl nitrite vapor by trapping them on the surface of the apparatus. The less-stable isomer A was transformed into isomer B upon heating or by dissolving it in a solvent. They formulated the A and B forms as Z- and E-isomers of diazine dioxides 3. The diazine dioxide structure for the nitroso dimers was later confirmed by NMR spectroscopy by Freeman." ... 

Many nitrosoalkane dimers in solution are in equihbrium with nitrosoalkane monomers at room temperature. De Boer and collaborators demonstrated that the photolysis of nitrosoalkane dimers in solution results in the formation of the corresponding nitroxides, as proved by ESR spectroscopy (Scheme 49)." The formation involves a combination of alkyl radicals generated from excited nitrosoalkanes with ground-state nitrosoalkanes. 

Carbazole oxidized by nickel peroxide in the absence of light and in the presence of 2-methyl-2-nitrosopropane gave the radical 71, an observation taken as additional evidence for the intermediacy of radical cations, trapped in this case by the nitrosoalkane, in oxidative dimerization of carbazoles (see Section II,A,2). 

At low concentrations of chlorine, dimeric nitrosoalkanes free from chlorine are produced when alkanes are treated also with nitric oxide. Under these circumstances, molecular chlorine is first converted into atomic chlorine which attacks the alkane to form alkyl radicals and hydrogen chloride. The alkyl radicals, in turn, form nitrosoalkanes with nitric oxide. This reaction is most effectively carried out when the ultraviolet radiation is between 380 and 420 mp. [43, 56],... 

Bis(nitrosoalkane), see Nitroso dimers p-Bromoazobenzene, 334 Bromomethylazobenzenes, 309 1 -Bromo-3-methyl-1,2-butadiene, 30... 

The bimolecular reduction of aliphatic nitroso compounds is complex and somewhat unreliable. With careful control of reaction conditions, a-nitroso ketones (in dimeric form) may be reduced with stannous chloride in an acidic medium at room temperature to the azoxy compounds, while dimeric a-nitroso acid derivatives may be reduced at about 50°C [10, 35, 36]. Nitrosoalkanes, on the other hand, are decomposed at room temperature to alcohols and nitrogen, and are reduced to amines at 50°-60°C. It has been postulated that only the dimeric nitroso compounds can be reduced to azoxy compounds and, in fact, that the dimer has a covalent nitrogen-nitrogen bond. Equations (31)—(34) summarize these data [10]. 

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%). 

Nitrogen Compounds. The aqueous Oxone-acetone combination has been developed for the transformation of certain anilines to the corresponding nitrobenzene derivatives, as exemplified in eq 15. This process involves sequential oxidation steps proceeding by way of an intermediate nitroso compound. In the case of primary aliphatic amines, other reactions of the nitrosoalkane species compete with the second oxidation step (for example, dimerization and tautomerization to the isomeric oxime), thereby limiting the synthetic generality of these oxidations. An overwhelming excess of aqueous Oxone has been used to convert cyclohexylamine to nitrocyclohexane (eq 16)P... 

However, stability of a dimer relative to its monomeric form depends on a variety of factors, which have been reviewed in an earlier paper. The same paper also described a novel method of catenation exemplified by the preparation of an oligomeric nitrosoalkane from 1,4-dinitrosocylohexane. Thus, bifunctional nitrosoalkanes with suitable structural features may have the potential to form poly [nitrosoalkanes] by the dimerization reaction. It was the objective of the present work to attempt poly-[nitrosoalkane] formation by using different bifunctional nitrosoalkanes and further try to obtain polymers of higher molecular weight. 

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