Hydrazones oxidations, benzene

Oxidation of ketone phenylhydrazones generates a radical-cation centre on the nitrogen atom adjacent to the benzene ring. The radical-cation is delocalised by both the hydrazone group and the phenyl ring. Reactions of 1,3,5-triphenyl-A -pyazolines illustrate the properties of these radical-cations. Two one-electron waves are seen at a rotating disc electrode in acetonitrile and for 1,3.5-triphenyl-pyrazoline, Ey. = 0.82 and 1.68 V vs. see [33]. The delocalised radical-cation is... 

The unconventional 3-diazoindoles were prepared by oxidative conversion of hydrazones and oximes. Thus, l-methyl-3-diazo-2-oxindole (21d) was prepared by mercuric oxide oxidation of l-methylisatin-3-hydrazone 297 (X = NNH2) in benzene at room temperature (1891JPR551) (Scheme 91). It can also be prepared by decomposition of l-methylisatin-3-tosyl-hydrazone 297 (X = NNHTs) with aqueous sodium hydroxide in a two-... 

The known disuhstituted ketencs include dialkyl-ketcnes, diary lkctcncs. and ihe ester analogs. Rimcthylkelene may be made from u-bromoisobuiy-ryl bromide by reaction with zinc in boiling ether, Diphenylketene may be made similarly, but the usual way lo prepare it is to oxidize benzil hydrazone with yellow mercuric oxide to benzoylphenyldiuzomethnne which, on healing in benzene solution, decomposes inio Ihe ketene. 

Bis(pyridinio)iodo]benzene triflate is a potent oxidant, as corroborated from polarographic measurements indeed, its E /2 value, +0.34 V, exceeds enormously that of DIB which has only — 1.0 V. For example, it converted hydrazones into diazo compounds and 1,2-bis hydrazones into alkynes, in good to excellent yields ... 

Certain cyclic acetylenic compounds can also be synthesized by this method, e.g., cyclodecyne209 in 36% yield by oxidation of 1,2-cyclodecanedione di-hydrazone with yellow mercuric oxide in benzene containing ethanolic potassium hydroxide solution and anhydrous sodium sulfate and cyclodecyne has been obtained similarly.210... 

The most commonly used synthesis of [l,2,3]triazolo[l,5-fl]pyridines remains that from the hydrazones of 2-p) idyl-carboxaldehydes or -ketones by oxidation. Some hydrazones give triazolop) dines when boiled in methanol in the presence of air, but all other reported cases require an added oxidant. The use of the most common oxidants illustrates the versatility of the synthesis. Nickel peroxide, potassium ferrocyanide and bicarbonate, air and a copper-II salt, manganese dioxide or (diacetoxyiodo)benzene have been used (02AHC1). An alternative route from tosylhydrazones of 2-pyridyl-carboxaldehydes or ketones by treatment with base, usually morpholine, has been used for high yields of sensitive materials (02AHC1). 

Potassium superoxide dissolved in benzene witli the aid of 18-crown-6 was shown to oxidize hydrazines, hydrazones and related compounds into a variety of products. The products resulted from oxidation, dimerization and condensation. A mechanism is proposed to account for the products. 

Dichlorobenzaldehyde hydrazone allowed to react with mercuric oxide in refluxing 1,2-dimethoxyethane in the presence of a little ethanolic KOH -> 2,6-didilorobenzonitrile. Y 80%. - In other solvents, such as benzene, diazo compds. are formed (s. Synth. Meth. 79, 354). F. e. and solvents s. D. B. Mobbs and H. Suschitzky, Tetrah. Let. 7977, 361. 

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