Dehydrogenation of hydrazo compounds

Dehydrogenation of hydrazo compounds with bromine, 32, 16 Dehydrohalogenation by sodium amide, 30, 72... 

A -Bromosuednimide is used in the dehydrogenation of hydrazo compounds to azo compounds [744] and in the oxidative degradation of a-hydroxy acids to aldehydes or ketones [745]. This reagent also oxidizes alkyl trimethylsilyl ethers to esters or ketones [744],... 

Diazo-compounds also result from the oxidative coupling of aromatic amines with bis-pyridinesilver permanganate, a new mild and selective oxidant, and from the two-phase dehydrogenation of hydrazo-compounds, utilising potassium hexacyanoferrate. °... 

The domain of oxidations with silver oxide includes the conversion of aldehydes into acids [63, 206, 362, 365, 366, 367 and of hydroxy aromatic compounds into quinones [171, 368, 369]. Less frequently, silver oxide is used for the oxidation of aldehyde and ketone hydrazones to diazo compounds [370, 371], of hydrazo compounds to azo compounds [372], and of hydroxylamines to nitroso compounds [373] or nitroxyls [374] and for the dehydrogenation of CH-NH bonds to -C=N- [375]. Similar results with silver carbonate are obtained in oxidations of alcohols to ketones [376] or acids [377] and of hydroxylamines to nitroso compounds [378]. 

A A -Bis(tosyl)sulphurdi-imide (33) was shown to be a useful reagent for the dehydrogenation of hydrazo- to azo-compounds as well as for the allylic... 

A variation of the Schmidt type reaction is the rearrangement of an azidocyc-loalkane, which is formed from the addition of hydrazoic acid to an cycloalkene. This reaction was used in the synthesis of muscopyridine (II/U4), a base isolated from the perfume gland of the musk deer [85]. In this context the reaction of II/115 as a model compound under the conditions of the Schmidt reaction gave a mixture of two compounds which after dehydrogenation yielded 11/116 and 11/117. The mechanism can be explained in terms of the migration of different bonds in the precursor. 

Hydrazo compounds are dehydrogenated to azo compounds by many oxidants. 2,2 -Bisazopropane is prepared by the oxidation of sym-diiso-propylhydrazine with cupric oxide (equation 491) [i5(9]. 

In a series of papers Lewis and co-workers have reported a comprehensive study of the photochemical reactions of azobenzenes in sulfuric acid. In the case of azobenzene itself, the products obtained were benzo[c]cinnoline (48%) together with benzidine (35%), and other azobenzenes gave products derived from the corresponding hydrazo compounds. The mechanism proposed is outlined in Scheme 2. There is an initial rapid establishment of a cis-trans equilibrium of monoprotonated azobenzene, with cyclization involving an excited form (14) of the cis-isomer, the lowest transition now being n-n. In the final step, dehydrogenation of the photocyclization product, 5,6-dihydrobenzo[c]cinnoline, is brought about by a second molecule of azobenzene, which is itself reduced to hydrazobenzene and... 

The procedure for preparation of hydrazobenzene and other hydrazo compounds must be uninterrupted and must involve exclusion of air, as these compounds are autoxidizable and are dehydrogenated to azo compounds by atmospheric oxygen. 

With GiO as carbocatalyst, oxidative cross condensations of various anihnes and ahphatic amines with benzyl amine to the corresponding Af-benzylidene derivatives have also been achieved by suppressing homocondensation of benzyl amine by using an excess of the cross-coupling partner [77]. Reduced GeO served as a reusable aerobic dehydrogenation catalyst for the preparation of azo compounds from their hydrazo precursors [79]. 

Efficient 2-phase dehydrogenation, e.g. of hydrazo to azo compounds, have been performed with phenoxyl radicals generated in situ by oxidation of phenols. ... 

By very careful hydrogenation (with stannous chloride in ethereal hydrogen chloride) phenyl azide has been converted into the exceedingly sensitive phenyltriazene (Dimroth), which, as has been shown, can be reconverted into the former by dehydrogenation. As in the case of the aliphatic diazo-compounds, an open chain structural formula has lately also been assigned to hydrazoic acid and its esters, so that the changes just mentioned may be formulated as follows ... 

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