Nitrolic acid

Dissolve a few drops of nitromethane in 10% sodium hydroxide solution. Add a few crystals of sodium nitrite and shake. Now add dilute sulphuric acid drop by drop. A brownish-red coloration develops, but fades again when an excess of acid is added. The sulphuric acid has thus liberated nitrous acid, which has in turn reacted with the nitromethane to give a nitrolic acid, the sodium salt of which is CH3NO2 + ONOH = CH(N02) N0H + HgO reddish-brown in colour, probably owing to mesomeric ions of the type ... 

O NCH NO 0 N CHN 0 An excess of sulphuric acid then converts the coloured sodium salt back to the almost colourless nitrolic acid. 

Primary nitro compound intense red colour, disappearing upon acidification. The colouration is that of the alkali salt of the nitrolic acid (nitro oxime) -... 

Reaction with nitrous acid can be used to differentiate primary, secondary, and tertiary mononitroparaffins. Primary nitroparaffins give nitrolic acids, which dissolve in alkali to form bright red salts. 

Furoxan nitrolic acid 34 was converted into isoxazoline 36 (96% yield) on storage in CH2CI2 solution in the presence of water (93CHE1099, 93KGS1283) (Scheme 12). The intermediate 35 could be trapped as [3 + 2] cycloaddition product 37. Reaction of nitrolic acid 34 with an excess of N2O4 also occurred via 35, giving 3-cyano-4-nitrofuroxan 38. 

Treatment of nitrolic acid 34, which is in turn available from hydroximino malonaldehyde dioxime (N2O4 in CH2CI2, 20 min, 10-15°C), with TFA gives furoxan-4-carboxylic acid in 35% yield (93CHE952, 93KGS1117) (Scheme 39). 

Pyruvonitrolic Acid. See under Acetylmethyl-nitrolic Acid in Vol 1, A84-L... 

Isolated salts of nitrolic acids , produced by action of nitrous acid on 1-nitroalka-nes, are explosive. 

Nitrile oxides generated under neutral conditions by thermal fragmentation of nitrolic acids 32, were trapped in situ with alkenes to afford isoxazolines 33 in 53-97% yields <00TL1191>. Nitrile oxides were also produced by treating O-silylated hydroxamic acids 34 with triflic anhydride and TEA . ... 

Z-Acetonitrolic acid rapidly loses N02 to form unstable acetonitrile oxide, which could be detected by monitoring its subsequent reactions (86). Arylnitrolic acids 12 (X = />-Cl. m-N02, o-N02) exist in the -configuration and undergo slow loss of N02 to give nitrile oxides. Subsequently it was shown (87) that nitrolic acids are converted to nitrile oxides in practically quantitative yields under neutral conditions (heating in THF). 

Nitrous acid converts -primary nitroparaffins into nitrolic acids and the secondary ones into so-called pseudonitroles, which latter, being nitroso-compounds, are coloured green or blue ... 

The nitrolic acids are colourless, hut dissolve in alkalis with a deep red colour because in addition to the chromogenic nitroso-group the aci-nitro-group is formed. The following formula is ascribed to the... 

If an aromatic compound contains saturated aliphatic side chains nitration carried out under the above conditions takes place always in the benzene nucleus and not in the side chain. Since the carbon atoms of benzene are each united directly to only one hydrogen atom, the nitro-derivatives obtained are tertiary and therefore incapable of forming salts, nitrolic acids, or pseudonitroles, as do the primary and secondary nitro-compounds. 

Victor Meyer also discovered the reactions of aliphatic nitro compounds with nitrous acid, which likewise depend on the activation of CH by NO221. Primary nitro compounds give nitrolic acids RC(N02) N0H, secondary nitro compounds give pseudo-nitroles R2C(N0)N02 and tertiary nitro compounds, having no activated CH, do not react. 

Phenyltrinitromethanes are similarly obtained from the nitration of gem-nitronitronate salts with a solution of dinitrogen tetroxide in ether. 1,1,1-Trinitroethane (73) can be formed in this way from the potassium salt of 1,1-dinitroethane (24). Nitrolic acids, the products formed... 

The tautomeric nitronic acids of secondary nitroalkanes or their nitronate salts react with nitrous acid or alkali metal nitrites to yield pseudonitroles.These pseudonitroles are often isolated as their colourless dimers (78b) but are deep blue in monomeric form (78a). Primary nitroalkanes also form pseudonitroles (80b) but these rapidly isomerise to the nitrolic acid (80a).Reactions are commonly conducted by slowly acidifying a mixture containing the nitronate salt and the metal nitrite, during which, the nitronic acid reacts with the nitrite anion. These reactions, first discovered by Meyer, have been used to prepare 2-nitroso-2-nitropropane (78a) and acetonitrolic acid (80a) from 2-nitropropane (76) and nitroethane (22) respectively. ... 

Pseudonitrole or nitrolic acid formation can be a side-reaction during the acidification of nitronate salts, particularly if the acid addition is slow. This process has been studied, optimized, and patented as a route to these compounds. " ... 

Three types of nitrosonitromethanides can be derived from the general formula [R (N02)C=N0] (R = H, NO, NO2, Table 1) nitrosonitromethanide (NNtM), dinitrosoni-tromethanide (DNNtM) and nitrosodinitromethanide (NDNtM). Experimentally known are only the sodium and potassium salts of the nitrolic acids. The nitrosonitromethanides, however, were only generated in situ in aqueous solutions. ... 

The class of nitrolic acids (nitro-oximes) was introduced by Victor Mayer as early as 1873 with the simplest representative methylnitroUc acid (HC(N02)=N0H) °. Tscher-niak, a student of Mayer, was the first to isolate the very labile methylnitroUc acid at low temperatures, while Wieland improved the synthesis by detailing the exact reaction conditions to increase the low yields. MethylnitroUc acid can be prepared as crystalline solid from nitromethane and KNO2/H2SO4 in situ generation of nitrous acid) in water at low temperatures, followed by extraction from this weak acidic solution into ether (Scheme 17). Removal of ether yields the pme, highly unstable free acid. Salts of methylnitroUc acid, NNtM, can be generated by extracting the acid into sodium carbonate solution. ... 

The first examples of furazan and furoxan nitrile oxides have been reported in the early 1990s. 4-Aminofurazan-3-carbonitrile oxide (65) was generated from the hydroximoyl chloride with base and its cycloaddition reactions investigated <92KGS687>, and the 4-phenyl analogue (66) is formed via the nitrolic acid derivative by treatment of the aldoxime with dinitrogen tetroxide <93LA44i>. Furazan-3-amidoximes react in the usual way with nitriles to yield 3-(furazan-3-yl)-1,2,4-oxadiazoles <9013941 >. 

Organic nitroxides (136a, 5), nitroparafins, and nitrolic acids (107) react with aqueous solutions of pentacyanocobaltate(II) salts to give alkyl pentacyanocobalt(III) nitroxide anion radicals, spin traps involving the formation of an N—Co bond (5). 

---