Hydrazo-benzene

When azo benzene is reduced or when the reduction of nitro benzene is continued beyond the stage of the azo compound we obtain hydrazo benzene, a colorless crystalline solid, m.p. 126°. The reduction may be accomplished (i) by using zinc and alcoholic sodium hydroxide, (2) by means of an alcoholic solution of ammonium sulphide or (3) electro-lytically in the presence of an alkali. 

Oxidation and Reduction.—Hydrazo compounds are usually colorless crystalline substances insoluble in water, but soluble in alcohol. They oxidize easily, even in the air, yielding the azo compound, and on reduction yield the amino compound. At high temperatures they often undergo a reciprocal oxidation and reduction of two molecules oiie being oxidized at the expense of the other which is thereby reduced, 37 

Thus hydrazo benzene reacts with itself and yields both azo benzene and aniline. 

Secondary Amines.— Like secondary amines the hydrazo compounds contain the (NH) group and toward nitrous acid hydrazo benzene reacts at low temperatures in the manner characteristic of this class of amines (p. 61) and yields a double nitroso amine compound. 

Benzidine.— The compound formed is known as benzidine, and is a di-amino derivative of a hydrocarbon consisting of two benzene rings directly linked together, known as di-phenyl. Both of these will be considered later (p. 730). 

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Examples of photoreduction processes, brought about by hydrogen abstraction from solvents are the reduction of azobenzene to hydrazo-benzene,81 of 2,3-diphenyl-5,8-quinoxalinedione (CXXXIII) to its hexahydro derivative,148 of pteroxyl-L-glutamic acid to dihydro-2-amino-4-hydroxypteridine-6-aldehyde,80 and of the blue gem-chloro-nitroso compounds CXXXIV-CXXXVI to the corresponding ketox-imes.189... 

Exercise 23-36 Treatment of a mixture of 2,2 dimethylhydrazobenzene and hydrazo-benzene with acid gives only 4,4 -diaminobiphenyl and 4,4 -diamino-2,2 -dimethyl-biphenyl. What does this tell you about the mechanism of this type of rearrangement Write a mechanism for the rearrangement of hydrazobenzene that is in accord with the acid catalysis (the rate depends on the square of the H concentration) and the lack of mixing of groups as described above. 

Dicyclohexylcarbodiimide n-Butylmalonic acid ethyl ester Hydrazo benzene... 

The parent hexahydro-l,2-diazepine (1, R = H) has been prepared.3 Condensation of 1,2-dicarbethoxyhydrazine and 1,5-dibromopentane in dimethylformamide in the presence of potassium gave 1 (R = C02Et) which could be hydrolyzed to 1 (R = H). The 1,2-dibenzoyl- and l,2-bis(anilinoformyl) derivatives of 1 were also prepared.3 In a similar manner the dilithium derivative of hydrazo-benzene and 1,5-diiodopentane gave 1 (R = C6H5).4... 

Electrolytic reduction of o-nitroj)heny arsinic acid in a sodium acetate solution, using a water-cooled platinum eatho[Pg.170]

It is also formed by the further reduction of azoxy benzene or by the oxidation of hydrazo benzene. 

This reaction shows clearly the relationship between these three compounds. By reduction azo benzene yields hydrazo benzene and then aniline. In this reduction the doubly linked nitrogen group is broken by the addition first of one hydrogen atom to each nitrogen and then by the addition of one more hydrogen atom to each nitrogen with the splitting of the double molecule into two molecules of aniline. 

Azo Compounds.— The term azo is derived from the French word for nitrogen, viz., azote. Compounds designated by the name azo or some modification of it, e.g.y azo benzene, oxy azo benzene, amino azo benzene, hydrazo benzene, azoxy benzene, etc. represent a class of compounds in which two nitrogen atoms, each of which is linked to a separate benzene ring, are directly linked to each other by a double or single bond. 

Derivatives of Di-amide.—We have discussed the relationship of hydrazo benzene to aniline and just as aniline is a derivative of one molecule of ammonia so hydrazo benzene may be considered as a derivative of two molecules of ammonia or better as a derivative of di-amide (p. 64), which is itself derived from two molecules of ammonia by the substitution of an amino group into ammonia itself. 

This 4- 4-di-amino di-phenyl is benzidine which yields a very important group of dyes and which is formed by a molecular rearrangement from hydrazo benzene (p. 578). ... 

The system azobenzene-hydrazobenzene is one of the rather few organic redox couples that behave reversibly or very nearly so at the dropping mercury electrode [187]. In nonaqueous solvents, like DMF, azobenzenes are reduced in two, one-electron steps The first one produces the radical anion, whereas the second one yields a hydrazo-benzene dianion. This dianion is easily protonated it has a tendency to decompose into arylhydrazine [188]. 

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