Oxidation of hydrazobenzene

In acetonitrile/water solvent hydrazobenzene is oxidised to azobenzene (Whal-ley et viz. 

Oxygen was excluded because it reacts directly with hydrazobenzene in acetonitrile/ water solvent. The kinetics are approximately second-order (first-order with respect to each reactant). The second-order rate coefficients increase with decreasing initial concentration of substrate, and with increasing initial concentration of peroxodisulphate. With equal concentrations of the reactants below 0.006 M the second-order rate coefficient is almost independent of the initial concentrations. Whalley et al. suggested the mechanism 

The rate equation derived from this mechanism is in accord with most of the observed features, but it predicts that with excess substrate the second-order rate coefficient should decrease during a run, whereas the observed rate coefficient always increases during a run, irrespective of whichever reactant is in excess. Whalley et al. suggest that incomplete dissociation of peroxodisulphate in the solvent might be responsible for the discrepancy. Another discrepancy is pointed out by Wilmarth and Haim, but these authors agree with Whalley et al. in concluding that the initiation step is reaction (91) rather than the spontaneous fission of the peroxodisulphate ion. 

---

Nitrogen Compound Autoxidation. CycHc processes based on the oxidation of hydrazobenzene and dihydrophenazine to give hydrogen peroxide and the corresponding azobenzene—phenazine were developed in the United States and Germany during World War II. However, these processes could not compete economically with the anthrahydroquinone autoxidation process. 

Azobenzenes may be prepared by oxidation of hydrazobenzenes this may be made in an undivided cell by reduction of the nitro compound with constant current [178]. Additionally, azobenzenes may be obtained in low to fair yield by anodic oxidation of aromatic amines at a rotating platinum screen cylinder anode in aqueous DMF [179]. 

Oxometal species have been variously invoked as intermediates in O-transfer reactions, especially in connection with single oxygen atom donors, such as iodosylbenzene, persulfate, N-oxides and peroxy compounds ". Oxocobalt(IV) was proposed as the active intermediate in the cobaloxime(II)-catalyzed oxidation of hydrazobenzene with 02 ... 

Owing to the great tendency of hydrazobenzene to undergo oxidation, all operations involving filtration should be carried out as rapidly as possible and air should not be drawn through it unnecessarily. The substance should be dried in a vacuum desiccator it can only be preserved in a colourless condition if it is kept in an atmosphere of carbon dioxide or nitrogen or in sealed vessels. 

Replacement of the methyl ketone moiety in 78 by a phenyl sulfoxide, interestingly, leads to a relatively potent uricosuric agent with diminished antiinflammatory action. This effect in lowering serum levels or uric acid leads to the use of this drug in the treatment of gout. Alkylation of diethyl malonate with the chlorosulfide, 79, gives the intermediate, 80. The pyrazolodione (81) is prepared in the usual way by condensation with hydrazobenzene. Careful oxidation of the sulfide with one equiv-... 

Aromatic azo compounds can be obtained by the oxidation of primary arylamines. The reagent most widely used for this purpose is activated manganese dioxide. This converts aniline and substituted anilines into the corresponding azo compounds in moderate to good yield. At room temperature the products are the n -azobenzenes, which are isomerized to the trans compounds on heating. It is probable that hydrazobenzenes are intermediates in the reaction, but these are more easily oxidized dim the starting anilines (Scheme 7). These oxidations are inhibited by electron-withdrawing substituents and some nitro-substituted anilines fail to react. 

Aromatic hydrazines like hydrazobenzene are readily oxidized to azobenzenes with air in the presence of alkali or by the action of sodium hypobromite. Aliphatic azo compounds are also prepared from the corresponding hydrazo compounds. Thus azomethane, CH5N=NCHj, is jjte-pared by the oxidation of sym-dimethylhydrazine with cupric chloride (70%). The oxidation of -hydrazotoluene, CjHsCHjNHNHCHjCjHs, to the azo compound is accomplished with mercuric oxide in boiling ether (76%). ... 

Diphenylpicrylhydrazyl, which is prepared from MA -diphenyl-A -(2,4,6-trinitrophenyl)hydrazine by oxidation with lead dioxide [982], is used for the dehydrogenation of 1,4-dihydronaphthalene to naphthalene and of hydrazobenzene to azobenzene [983]. Simpler and cheaper compounds are, however, available for such purposes (equation 21). 

Dehydroifenatiun. I>iethyl azodicarboxylme has been shown lo elt eci photochemical dehydrogenation of isopropanol to pinacol" and of cyclohexunol lo cyclohexanone. Actually the reagent eifects nonphotochemical oxidation of alcohols, mercaptans, anilines, and hydrazobenzenes with formation of diethyl hydrazinodicarboxylate. ... 

A primary amine having an a-methylene group is oxidized by the reagent in methylene chloride in part to the nitrile and in part to the aldehyde, both in very low yield. The reagent oxidizes hydrazobenzene to azobenzene and effects Beckmann rearrangement of oximes. The most significant use is for oxidation of /-butylamine... 

Oxidation. Bismuthines accept oxygen from iodosylbenzene under ultrasonic irradiation. These AraBiO are mild oxidants, which convert benzylic, allylic, and secondary alcohols to carbonyl compounds, hydrazobenzenes to azobenzenes. By contrast, oxides of lower pnictogen elements are devoid of oxidizing power for organic substances. 

---