Secondary nitroalkanes, nitration

Olsen and co-workers reported the nitration of secondary nitroalkanes to m-dinitro compounds with nitronium tetrafluoroborate in acetonitrile at 0 °C. Yields are lower compared to the Kaplan-Shechter reaction and significant amounts of pseudonitroles are formed, but this is possibly due to impure reagent. 

Oxidative nitration, a process discovered by Kaplan and Shechter, is probably the most efficient and useful method available for the synthesis of em-dinitroaliphatic compounds from the corresponding nitroalkanes. The process, which is an electron-transfer substitution at saturated carbon, involves treatment of the nitronate salts of primary or secondary nitroalkanes with silver nitrate and an inorganic nitrite in neutral or alkali media. The reaction is believed ° °° to proceed through the addition complex (82) which collapses and leads to oxidative addition of nitrite anion to the nitronate and reduction of silver from Ag+ to Ag . Reactions proceed rapidly in homogeneous solution between 0 and 30 °C. 

A range of primary and secondary nitroalkanes and their derivatives have been converted to the corresponding gem-dinitroalkanes via oxidative nitration, including the conversion of nitroethane, 1-nitropropane, 2-nitropropane and 2-nitro-1,3-propanediol to 1,1-dinitroethane (78 %), 1,1-dinitropropane (86 %), 2,2-dinitropropane (93 %) and 2,2-dinitro-1,3-propanediol (77 %) respectively. The silver nitrate used in these reactions can be recovered quantitatively on a laboratory scale and this has led to a study where oxidative nitration has been considered for the large-scale production of 2,2-dinitropropanol (25) from the nitroethane (22). ... 

Nitric acid (70 %) or the mixture of nitric acid and sulfuric acid or other mixed acids with catalytic function can nitrate secondary nitroalkanes directly into gem-inal dinitroalkane [8]. With the sodium alkoxide and tetranitromethane, primary nitroalkanes can be nitrated into dinitroalkanes and trinitroalkanes [9]. In a neutral or basic solvent, primary, secondary nitroalkane salts can be nitrated, step by step, into gem-dinitroalkanes by silver nitrate and sodium nitrite [10]. Alkali metal salts of aryl nitroalkanes can be nitrated, step by step, into dinitroalkanes and trinitroalkanes by dinitrogen tetroxide [11]. 

Primary amines containing primary alkyl groups can be converted into aldehydes by oxidation of the triazole derivative (4) with diethyl azodicarboxylate (Scheme 1). Primary and secondary nitroalkanes can be transformed into the corresponding aldehydes and ketones either by hydrogen peroxide in aqueous methanol containing potassium carbonate" or by treatment with ceric ammonium nitrate in aqueous acetonitrile containing triethylamine. These methods offer further mild conditions as alternatives to the well known Nef reaction. 

Nitro-compounds are also prepared by the replacement of benzylic hydroxyl by 2-nitropropyl groups," the replacement of activated bromine with silver nitrate in the presence of triphenylphosphine," and the Michael addition of nitroethane to a,/3-ethylenesulphoximines under phase-transfer conditions." The preparation and reactions of cyclic a-nitroketones have been reviewed." The conversion of primary and secondary nitroalkanes into the corresponding carbonyl compounds, i.e. the Nef reaction, is a useful synthetic transformation. Three new methods" " to effect this important reaction offer a variety of oxidative conditions, and thus enable the minimization of side reactions (Scheme 36). 

The most important reactions of nitroalkan.es are those involving the a hydrogens of the primary and secondary compounds. For example, nitro-methane is sufficiently acidic to dissolve in aqueous hydroxide solutions. The anion so produced has an electronic structure analogous to the nitrate anion ... 

Mixture of nitric and sulfuric acid (mixed acid) used extensively in nitration of aromatic hydrocarbons, is generally unsuitable for nitration of alkanes, since primary nitroalkanes are rapidly hydrolyzed by hot sulfuric acid and secondary and tertiary nitroalkanes form tars (in all probability via rapid alkene-forming elimination and subsequent polycondensation, polymerization, etc.). It is, however, significant to point out that it is not necessarily the lack of reactivity of paraffins with mixed acid that makes the nitration of saturated hydrocarbons unsuitable, but that fast secondary reactions of any nitro products formed (as well as oxidative side reactions) can take place. This difficulty can be, at least in part, overcome by using preformed nitronium salts as nitrating agents. 

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