Nitrones Nitronic acids

The nitroparaffins are named as derivatives of the corresponding hydrocarbons by usiag the prefix "nitro" to designate the NO2 group (1), eg, 1,1-dinitroethane, CH2CH(N02)2- The salts obtained from nitroparaffins and the so-called nitronic acids are identical and may be named as derivatives of either, eg, sodium salt of i7ti-nitromethane, or sodium methanenitronate [25854-38-0]. 

Tautomerism. Primary and secondary mononitroparaffias are acidic substances which exist ia tautomeric equiUbria with thek nitronic acids. 

The nitro isomer is weaMy acidic the nitronic acid isomer (aci form) is much more acidic. A comparison of the ionisation constants of the two forms ki water at 25°C is given ki Table 4. 

Acidification of mononitroparaffin salts immediately gives the nitronic acid. Many nitronic acids have been isolated and stored as crystalline soflds. 

In solution, a nitronic acid either isomerizes slowly into its more stable nitro form or undergoes some kreversible transformation. The isomerization occurs sufficiently slowly that it can be measured by conductometric or halometric methods. 

Like isomerization of oxaziridines to nitrones, acid hydrolysis of oxaziridines proceeds with conservation of the N—O bond. Both reactions are related mechanistically and are... 

The nitro form is much more stable than the aci form in sharp contrast to the parallel case of nitroso-oxime tautomerism, undoubtedly because the nitro form has resonance not found in the nitroso case. Aci forms of nitro compounds are also called nitronic acids and azinic acids. 

Actually, nitronates are the closest related derivatives of nitronic acids, that is, aci forms of AN, which exist in labile equilibrium with true AN. Some derivatives of nitronic acids, —CH=N(0)0X, where OX is the good leaving group, are evident intermediates in the most well-developed procedures for the synthesis of nitrile oxides from primary AN. In this chapter, special emphasis is given to particular nitronates, which are generated from a-functionalized AN and can also be considered as precursors of a-functionalized nitrile oxides. 

Owing to the fact that silyl esters of nitronic acids (SENAs) are readily available, rather stable, and exhibit various reactivities, these compounds have attracted considerable interest in the chemistry of nitronates. 

Analogous tautomerism 98 =99 has been observed earlier for similar functionalized nitronic acids (294) (Scheme 3.81). 

Time-resolved resonance Raman spectroscopy has been used to study the photorearrangement of o-nitrobenzyl esters in polar and protic solvents53 in acetonitrile, the only primary photoproduct is nitronic acid 68 with a lifetime of 80 microsecond, while in methanol the nitronic acid exists in equilibrium with the nitronate anion 69, giving a lifetime of 100 microseconds (equation 41). 

In some cases80 where the nitro group is ortho to an ethyl group, there is a competing reaction which leads, via cyclization probably involving the nitronic acid form of the nitro group, to the corresponding anthranil 71. 

The kinetics and thermodynamics of the act-nitro equilibrium of picrylacetone (105) in 50 50 and 30 70 (v/v) H20-MC2S0 mixtures have been reported. Rate of general base-catalysed deprotonation of (105) and general acid-catalysed reprotonation of the resulting anion (106) have been monitored at low pH a fast equilibrium protonation of (106) to give a directly observable short-lived nitronic acid species (107) has been found to precede conversion to (105). The constants pAf and pATj,... 

Nitronate salts and the tautomeric act-form of nitroalkanes, known as nitronic acids, are converted to gem-dinitro compounds on treatment with dinitrogen tetroxide. Novikov and co-workers synthesized phenyldinitromethane by treating phenylnitromethane with dinitrogen tetroxide in ether and later reported the synthesis of some substituted phenyltrinitromethanes from the direct nitration of the nitronate salts of phenylnitromethanes. 

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. ... 

Nadolol, 110 Nafenopin, 214 Nafomine, 212 NafT-onyl, 213 Nalbuphine, 319 Nalidixic acid, 370, 469 Nalmexone, 319 Nalorphine, 318 Naloxone, 318, 323 Naltrexone, 319 Naranol, 454 Nef reaction, 2 Nefopam, 447 Nequinate, 369 Nexeridine, 17 Nicergoline, 478 Niclos amide, 94 Nifedipine, 283 Nifuratrone, 238 Nifurdazil, 239 Nifurimide, 239 Nifui oxime, 238 Nifurpirinol, 240 Nifurcguinazol, 383 Nifursemizone, 238 Nifurthiazole, 241 Nimazone, 260 Nimorazole, 244 Niridazole, 269 Nisobamate, 22 Nithiazole, 268 Nitronic acid, 2 Nivazol, 159 Nocardicins, 435 Noracymethadol, 58... 

E. Brener, Nitrones and Nitronic Acid Derivatives Their Structure and their Roles in Synthesis , in The Chemistry of Amino, Nitroso and Nitro Compounds and their Derivatives, Vol. 1, S. Patai ed., Wiley, Chichester, 1982, pp. 459-538. 

The [3 + 2] cycloaddition of silyl nitronates has been extensively investigated since the first pioneering studies by Ioffe et al. (16). This transformation is attractive because of the resulting isoxazolidine can be easily converted to the corresponding isoxazoline for which a myriad of transformations are known. Moreover, this procedure provides yields and selectivities different from those of the nitrile oxide [3 + 2] cycloaddition, which affords the isoxazoline directly. The reaction of silyl nitronates has been briefly reviewed in the context of the chemistry of nitronic acid derivatives (27,30). 

In an analogous manner, nitroalkenes can be utilized as the electrophile in a tandem coupling-cyclization process (Eq. 2.18). Addition of a stabilized sulfonium ylide such as 209, to a variety of nitroalkenes provides an intermediate nitronic acid, which upon displacement of dimethyl sulfide provides a mixture of the corresponding nitrocyclopropane (XL) and cyclic nitronate (XLI). The ratio of products is highly dependent on the structure of the nitroalkene. For example, without a substituent on the a-position of the nitroalkene (R = H), only the... 

E. Breuer, Nitrones and Nitronic Acid Derivatives an Update in S. Patai u. Z. Rappoport, Nitrones,... 

Dihydro-5-isonitro-4,-methyl-4-methylene-1,1, 5 -trinitro-2,2 -biimidazole Methyl Ester or 4-Methyf-4,-methylene-1,1l,5I-trinitro-2,2 -biimidazole-5 -nitronic Acid Methyl Ester,... 

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