Tautomerism, nitro compounds oxide

There are three possible products when NOCl is added to alkenes, a (3-halo nitro-so compound, an oxime, or a (3-halo nitro compound.The initial product is always the (3-halo nitroso compound, but these are stable only if the carbon bearing the nitrogen has no hydrogen. If it has, the nitroso compound tautomerizes to the oxime, H—C-N=0 C=N-OH. With some alkenes, the initial (3-halo nitroso compound is oxidized by the NOCl to a (3-halo nitro compound. Many functional groups can be present without interference (e.g., COOH, COOR, CN, OR). The mechanism in most cases is probably simple electrophilic addition, and the addition is usually anti, although syn addition has been reported in some cases.Markovnikov s mle is followed, the positive NO going to the carbon that has more hydrogens. 

V -(2-Aminophenyl)hydrazides are cyclized to 5 and oxidized to 1,2,4-benzotriazines 6 when treated with hydrochloric acid and sodium 3-nitrobenzenesulfonate.5,147 Similarly, A -(2-nitro-phenyl)hydrazides give 1,2-dihydro-l, 2,4-benzotriazines 5 when the nitro group is reduced with sodium amalgam in ethanol. In most cases, the initially formed dihydro compounds are not isolated, but are oxidized by potassium hexacyanoferrate(III) to the aromatic 1,2,4-benzotriazines 6.148 Reduction of the nitrohydrazones or the tautomeric azo compounds with zinc, catalytic hydrogenation,332 or elcctrochemically246 affords 1,2,4-benzotriazines 6.148 Electrochemical reduction of A"-(2-nitrophenyl)hydrazides yields 3-substituted 1,2,4-benzotriazines 6.140... 

Another type of reaction may be mentioned here, which, while not oxidation-reduction, shows some of the possibilities in the way of relative oxidizing potentials of different atoms, or the relative aflSnities of the atoms for valence electrons. Silver nitrite ind sodiuiii nitrite when treated with an alkyl halide give different products. With the former, a nitro compound is obtained mainly with the latter a nitrite predominates. While according to the older views, this would point to different structures for the two nitrites, according to the principles developed in this book, the explanation of these differences involves tautomerism and several chemical equilibria. The reaction may be given in general terms as follows ... 

Substitution of the 4-nitro group in 3,4-dinitrofuroxan 1176 by ammonia occurs readily, even at low temperature. Subsequent treatment of the obtained amine, product 1177, with r-butylamine results in formation of 4-amino-2-(/-butyl)-5-nitro-l,2,3-triazole 1-oxide 1178. However, there must be some additional side products in the reaction mixture, as the isolated yield of compound 1178 is only 17%. Upon treatment with trifluoroperacetic acid, the r-butyl group is removed. The obtained triazole system can exist in two tautomeric forms, 1179 and 1180 however, the 1-oxide form 1179 is strongly favored (Scheme 195) <2003CHE608>. 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

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