Azobenzene, chlorination

Chlorination of the azobenzene complex 463 with chlorine produces mono-chloroazobenzene with regeneration of PdCN. Then complex formation takes place again with the chlorinated azobenzene. By this sequence, finally tetra-chloroazobenzene (503) is obtained using a catalytic amount of PdCT. The reaction, carried out by passing chlorine gas into an aqueous dioxane solution of azobenzene and PdCf for 16 h, gives a mixture of polychlorinated azoben-zenes[455]. 

Finally, in the azobenzene series it has been found16 that during reaction, exchange of chlorine for hydrogen may occur above 60°C, as illustrated by the case of 3-chloro-4-methyl-4 -dimethylaminoazoben-zene (25), which, depending on reaction temperature, reacts with benzalaniline to yield either the expected stilbene (26) or its dechlorinated analog (27). 

Ammonium hexacyanoferrate(II), 2572 f Arsine, 0100 Azido-2-butyne, 1469 3-Azidopropyne, 1111 cis-Azobenzene, 3478 Azoxybenzene, 3479 Barium azide, 0214 Benzenediazonium nitrate, 2268 Benzotriazole, 2262 Borane, 0135 Bromine azide, 0256 f 3-Bromopropyne, 1087 f 1,2-Butadiene, 1475 f 1,3-Butadiene, 1476 f Buten-3-yne, 1419 f 1-Butyne, 1477 f 2-Butyne, 1478 Cadmium azide, 3951 Cadmium cyanide, 0585 Cadmium fulminate, 0586 Cadmium nitride, 3954 Calcium azide, 3930 t Carbon disulfide, 0557 Chlorine dioxide, 4036 Chloroacetylene, 0648... 

Gilbert P, Saint-Ruf G, Poncelet F, et al. 1980. Genetic effects of chlorinated anilines and azobenzenes on Salmonella typhimurium. Arch Environ Contam Toxicol 9 533-541. 

Cyanuric chloride on monosubstitution with nucleophiles such as methanol or 4-amino-azobenzene followed by displacement of a second chlorine with alanine amide gave compounds which are used for precolumn derivatization of amino acids. The diastereoisomers formed are resolved by reverse-phase HPLC <92MI 6l2-0i>. Enantiomeric amino acids are separated by HPLC on bis[carbamoyl(alkyl)methylamino]-6-chloro-l,3,5-triazine derived stationary phases <93JC277>. 

The reaction of chlorine with the azobenzene complex affords ortho-chlorinated azobenzene, and palladium chloride is regenerated 112). 

Sodium Amalgam. Sodium amalgam reduces nitrobenzene to azobenzene as well as to hydrazobenzene knd oximes to amines. The I. G. Farben-industrie, in its development of mercury cells for the production of chlorine and caustic, found that it could lise the intermediate sodium amalgam for the reduction of nitrobenzene to ajzobenzene on a very economical basis. The operation was carried out in batches in nickel reactors, and 50 per cent caustic soda was obtained simultaneously. It was not found feasible to produce hydrazobenzene directly by this method. Hallie has, however, obtained a patent on the reduction of nitrobenzei e to hydrazobenzene using sodium amalgam in aqueous alcohol. 

The best known of these is the ozonation of tertiary amines to amine oxides (II) (i). Henbest and Stratford (11) and Shulman (17) have shown that competing with this is an ozone attack on the alpha position of an alkyl side chain to produce various decomposition products of III. Henbest (11) showed that amine oxide formation is favored in chloroform and methanol, while side chain oxidation is predominant in hydrocarbon solvents. Also of considerable interest are the reported conversions, during ozonation, of phenylenediamines to Wursters salts (VII) (8, 14), of liquid ammonia to ammonium ozonate (VA) at a low temperature 18), and of amines to amine hydrochlorides (VB) in chlorinated hydrocarbon solvents 17, 19), Finally, an early report states that azobenzene and quinone are obtained upon ozonation of aniline (15). 

Scheme 12 Catalytic chlorination of azobenzene via the proposed Pd(II)/ Pd(IV) catalytic cycle. The first directing group-assisted electrophilic halogenation reaction...

The reaction of Scheme 11 is validated for RX = Br2 by the NMR detection of all four species in the proposed cycle and illustrates again a system where aryl halide involvement is readily explained in the same way but with the severe reservations expressed above for other systems. Facile cyclopalladation of azobenzene, oxidation of Pd(II) by chlorine (e.g., formation of 16), and reductive elimination via C—Cl coupling... 

Many other types of ECP have been described. These include PS-block-PPO [61], boron containing PVA [62], polyethylene dioxythiophene/polystyrene sulfonate [65], PC-ABS composites [64], PEO composites [64], PEO complexes with sodium lanthanum tetrafluoride [63], chlorine substituted PANI [70], PVP-PVA coupled with potassium bromate [57], PANI-PA 6,6 composite films [72], talc-PPY composites [54], epoxy resin alpha-haematite nanorod composites [56], PP-montmorillonite composites [69], magnetite containing polymers [105], LDPE [27], PC-acrylonitrile-butadiene composites [106], sodium ion conducting PEO complexed with sodium lanthanum tetrafluoride [63], PVDE [107], PANI composites [108], PP novolac resins [109], dendrimers containing light switchable azobenzene [110],PVP/PVA [107] and PPY[111]. 

Fahey reported the Pd-catalyzed directed aromatic C-H chlorination of azobenzene using CI2 in 1970 (Fig. 29) [112, 113], and Sanford reported the Pd-catalyzed directed aromatic C-H chlorination of 2-aiylpyridines with A -chlorosuccinimide (NCS) in 2004 (chlorination reaction shown in Fig. 30) [105, 114-116]. 

Chlorinated anilines are aerobically degraded, by both soil and sewage microorganisms, the monochloro-compounds more readily than the dichloro-derivatives. Chloroanilines are formed in soil as part of the degradation process of the substituted urea herbicides [70]. An alternative pathway is the production of substituted azobenzenes, by dehydrogenation-condensation involving two amino groups. 

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