Azobenzene Benzidine

A range of products was obtained from aniline including those from oxidative coupling (azozybenzene, azobenzene, and benzidine), and phenazine by dimerization (Chan and Larson 1991). Oxidation of m-phenylenediamine was initiated by the oxidation of two molecules to produce an A-phenyl-2-aminoquinone-imine that reacted with m-phenylenediamine to produce 2-amino-5-phenylaminoquinone-imine after further oxidation (Kami et al. 2000). 

All ECi adsorption coupled mechanisms have been verified by experiments with azobenzene/hydrazobenzene redox couple at a hanging mercury drop electrode [86,128,130]. As mentioned in Sect. 2.5.3, azobenzene undergoes a two-electron and two-proton chemically reversible reduction to hydrazobenzene (reaction 2.202). In an acidic medium, hydrazobenzene rearranges to electrochemically inactive benzidine, through a chemically irreversible follow-up chemical reaction (reaction 2.203). The rate of benzidine rearrangement is controlled by the proton concentration in the electrolyte solution. Both azobenzene and hydrazobenzene, and probably benzidine, adsorb strongly on the mercury electrode surface. 

Uses Solvent for cellulose ethers modifying esterification of cellulose acetate ingredient of metal polishes and shoe polishes manufacture of aniline, benzidine, quinoline, azobenzene, drugs, photographic chemicals. 

Benzidines (Method 605). The method chosen for the determination of benzidine and 3,3 -dichlorobenzidine uses HPLC. Lichrosorb RP-2 (5 jLtm) is used as the analytical column, and acetonitrile and an acetate buffer are used as the mobile phase. A relatively selective electrochemical detector is used to detect and measure the benzidines. The instability of 1,2-diphenylhydrazine, which decomposes to azobenzene, caused it to be eliminated from consideration. 

Richfield-Fratz et al. (206) determined aniline, benzidine, 4-aminophenyl, and 4-amino-azobenzene in sunset yellow. The determination involved chloroform extraction followed by diazotization and coupling with the disodium salt of 3-hydroxy-2,7-naphthalenedisulfonic acid and analysis by reverse-phase HPLC. Using a similar system, Peiperl et al. (207) determined benzidine in sunset yellow. Dithionite was used to reduce any combined benzidine present. 

It has been known for some time that irradiation of azobenzene (324) in either 22 N sulfuric acid350 351 or acetic acid with added ferric chloride 352 yields benzo[c]cinnoline (325). This is accompanied by the formation of an almost equal quantity of benzidine (326), undoubtedly arising by rearrangement of hydrazobenzene (327). The mechanism of this reaction differs, therefore, from that of the stilbene cyclodehydrogenation, and azobenzene itself functions as the hydrogen acceptor. Yields of not more than 50% of benzo[c]cinnoline are generally observed. 

This work was extended by Elbs and his pupils,1 and the processes were protected by patents.2 Subsequently alcohol was dispensed with and aqueous caustic soda employed. For example, an emulsion of nitrobenzene in 10 per cent, aqueous sodium hydroxide may be reduced with a cathode of lead or nickel in a porous earthenware cell, with a current density of 10-12 amps, per dm.2 An anode of graphite or lead may be employed in an outer containing vessel filled with sodium hydroxide solution or sodium sulphate. Azo- or hydrazobenzene is obtained according to the quantity of electricity passed through, and the azobenzene emulsion can be transformed into benzidine by acidifying the cathode liquor and completing the reduction.4... 

Vanadium2 compounds may be employed as catalysts in oxidation, and reduction processes. Por example, anthracene is oxidised to anthraquinone with a lead anode in 20 per cent, sulphuric acid which contains 3 per cent, of vanadic acid. Aniline under similar conditions may be oxidised to benzoquinone, and the latter substance can be efficiently reduced to hydroquinone. Azobenzene and azoxybenzene are stated to give a good yield of benzidine... 

Tetraphenylethylene cyclizes anodically to 9,10-diphenylphenanthrene analogously to its photooxidative cyclization. The attempted anodic cyclization of cis- or frans-stilbene to phenanthrene however failed due to electrophilic reaction of the intermediate radical cation with the solvent 37S Primary aromatic amines are oxidized to radical cations which, depending on the pH of the electrolyte couple to aminodiphenylamines (C-N coupling (84) in Eq. (172) ), yield benzidines (85) at low pH (C-C coupling) or dimerize to hydrazobenzene (86) (N-N coupling) which is subsequently oxidized to azobenzene (Eq. (172) ) 2 5,376,377)... 

Hydroxyethyl)-2-methyl-5-nitro-imidaaole (metronidazole) H-Nitrosoethylurea Methylbis(2-chloroethyl) amine Cyclophosphamide Benzidine Azobenzene... 

Mercury, nickel, copper, zinc, lead, iron, brass, and zinc amalgam were tried as electrode material in respect to their reduction behavior in the reduction of azobenzene to benzidine in alcohol-sulphuric—acid solution. It was shown that the furthest utilizable reduction was obtained with mercury the usefulness of the other metals was determined to be in the following order Lead, sheet nickel, nickel-wire gauze, copper, zinc, iron, and brass. 

Besides azoxybenzene, azobenzene also gives hydrazobenzene, as already mentioned, e.g. in acid solution benzidine results. Azobenzene, however, is formed only in very small quantity. 

Lob,3 convinced of the futility of thus being able to obtain a good yield of benzidine by a direct reduction of nitrobenzene in acid solution, sought to carry out the benzidine process by a careful realization of the conditions theoretically required— primary preparation of azoxy- or azobenzene in the best quantitative yields, i.e. in electrolytes, containing alkali or alkali-salt, then reducing these products in acid solution. Two processes thus resulted. In the first one the electrolytic reduction was carried out to azobenzene in alcoholic-alkaline solution, then the cathode solution was acidified with sulphuric acid, and the further reduction and molecular rearrangement combined in one operation. The second process, which was... 

An example of the application of the technique is a study of the kinetics of the benzidine rearrangement, which follows the reduction of azobenzene in acidic aqueous ethanol [205]. The approach has been further developed and extended to encompass the automatic recording of three-dimensional i-E-t curves [206]. However, experiments of this kind may be hard to perform with high precision because of difficulties in the accurate control of the potential in the region close to E°. 

Para-Substituted anilines are oxidized in low to moderate yields to azobenzenes in basic solution (Table 5, number 4a). By elimination of one / ara-substituent (Cl or OMe) during the reaction, they can also couple to 4-substituted 4-aminodiphenyla-mines [76]. Carbon-carbon coupling can occur with 4-substituted arylamines as substrates. The / ara-substituent is eliminated and a / ara-benzidine is obtained (Table 5, number 6), ortho carbon-carbon coupling occurs (number 7), or a benzyl radical is formed, which subsequently couples (number 8). The ortho- and mera-substituted anilines yield at graphite cloth electrodes in 6iV H2SO4 substituted benzidines and 4-aminodiphenylamines. The latter products are converted by further oxidation and hydrolysis to 2-substituted / (7ra-benzoquinones, sometimes in substantial yields (e.g., 35%) [81],... 

Aminobiphenyl <15ppb Aniline <250ppb Azobenzene <200ppb Benzidine [Pg.198]

Azobenzene and its derivative hydrazobenzene may be converted into a derivative of diphenyl, benzidine and the ease with which this reaction takes place seems to point to the existence of an unstable linkage between the benzene rings. This would be most readily explained by the assumption that a change in the linkage (from double to single) between the carbon atoms in the benzene chain takes place in a similar manner to the linkage in the quinone formula. 

The results reported in Reference 18 need some comments. First, Sharma and coworkers25, who studied oxidative voltammetry of aniline on graphite electrodes in acidic conditions, observed that in 0.1 M sulfuric acid the radical cation (4) undergoes not only head-to-tail and tail-to-tail but also head-to-head coupling to form p-aminodiphenylamine, benzidine and hydrazobenzene (23), respectively 23 is oxidizable to azobenzene (24). 

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