Nitration, of alkanes

Another reaction of commercial importance is the nitration of alkanes to give nitroparaffins. Such reactions usually are carried out in the vapor phase at elevated temperatures using nitric acid (HN03) or nitrogen tetroxide (N204) as the nitrating agent  

All available evidence points to a radical mechanism for nitration, but many aspects of the reaction are not fully understood. Mixtures are obtained nitration of propane gives not only 1- and 2-nitropropanes but nitroethane and nitromethane  

In commercial practice, the yield and product distribution in nitration of alkanes is controlled as far as possible by the judicious addition of catalysts (e.g., oxygen and halogens), which are believed to raise the concentration of alkyl radicals. The products are separated from the mixtures by fractional distillation. 

Huyser, Free-Radical Chain Reactions, Wiley-lnterscience, New York, 1970. 

Westrum, Jr., and G. C. Sinke, The Chemical Thermodynamics of Organic Compounds, John Wiley and Sons, Inc., New York, 1969. Summarizes AH° of formation of some 4500 organic compounds and AG° values for about half that many. Includes many valuable descriptions of the use of thermodynamic data in the planning of industrial processes. 

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Nitration of alkanes can be carried out in the gas phase at 400°C or in the liquid phase. The reaction is not practical for the production of pure products for any alkane except methane. For other alkanes, not only does the reaction produce mixtures of the mono-, di-, and polynitrated alkanes at every combination of positions, but extensive chain cleavage occurs. A free-radical mechanism is involved. ... 

Organic synthesis 51 [OS 51) Nitration of alkanes such as methane and hexane with... 

The kinetics and mechanism of iV-nitration reactions have been reviewed and the nitration of alkanes with nitronium hexafluorophosphate in CH2CI2 or EtN02 has been shown to involve direct electrophilic insertion of NO2+ into C-H and C-C a-bonds. ... 

V.Y Shtem, KhimKinetTsepnyeReakts, InstKhimFizAkadNauk 1966, 286—322 CA 66, 54671(1967) (Review with 33 refs) (Vapor phase nitration of alkanes by nitrogen dioxide)... 

The nitration of alkanes and that of alkylaromatics at the side chain can be accomplished with nitric acid or nitrogen oxides in either the liquid or the vapor... 

Nitration of alkanes is successful only when conducted at high temperatures in the vapor phase. Mixtures of products are invariably obtained (Section 4-6) ... 

The catalytic oxidation of cyclohexane is performed in the liquid phase with air as reactant and in the presence of a catalyst. The resulting product is a mixture of alcohol and ketone (Table 1, entry 12) [19]. To limit formation of side-products (adipic, glutaric, and succinic acids) conversion is limited to 10-12 %. In a process developed by To ray a gas mixture containing HC1 and nitrosyl chloride is reacted with cyclohexane, with initiation by light, forming the oxime directly (Table 1, entry 12). The corrosiveness of the nitrosyl chloride causes massive problems, however [20]. The nitration of alkanes (Table 1, entry 13) became important in a liquid-phase reaction producing nitrocyclohexane which was further catalytically hydrated forming the oxime. 

Electrophilic nitration of alkanes has been performed with nitronium salts, for example, NO2 PFe and with HNO3-H2SO4 mixtures, but mixtures of nitration and cleavage products are obtained and yields are generally low. ° The reaction of alkanes with nitric acid and A-hydroxysuccinimide (NHS), however, gave moderate-to-good yields of the corresponding nitroalkane. Similar nitration was accomplished with NO2, NHS and air. "... 

As is known (Vol. I). alkanes can be nitrated in vapour phase by nitric acid or nitrogen dioxide. Nitration with nitric acid at temperatures of 400-435 C (method of Hass, Vol. I. p. 86) became a well established commercial method of making nitroalkanes. A considerable number of papers mainly by Hass and co-workers (Vol. 1) and Titov (Vol. I) gave both theoretical and practical foundations for this remarkable process and subsequently less theoretical work has appeared. Less attention was paid to the nitration of alkanes with nitrogen... 

FIG. 30. Sicngcl-Eagli nitrator of alkanes used by Commercial Solvents... 

Maiasa [100] discussed the problem of the hazards of the nitration of alkanes. In his remarkably important paper he considered. ... 

The first examples of the conversion of nitroalkanes to carbonyl compounds were described in 1893 by Konovaloff, who was examining the reactivity of nitroalkanes obtained from nitration of alkanes with nitric acid.1 Konovaloff reported that treatment of 2-nitrohexane (3) with strong soda (NaOH) followed by reaction with Zn/HOAc afforded a mixture of methyl butyl ketone (4) and 2-aminohexane (5). Additionally, the reaction of the potassium salt of 2-phenylnitroethane with dilute aqueous acid provided mixtures of acetophenone and 2-phenylnitroethane. 

The products of these reactions are carbocations or olefins which are in equilibrium with the carbocations. Mechanisms involving structures VIII-13-VIII-14 can be only hardly discriminated. The only evidence for the mechanism of electrophilic substitution might be the deep similarity in selectivity and KIE for the reactions between palladium(ll) and alkanes on the one hand, and nitration of alkanes with NOz on the other hand. Indeed, such a similarity has been evaluated in the study of the temperature dependencies of KIE and 5/6 effects. 

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