Nitrobenzene as oxidant

In the preparation of a dyestuff from aniline, nitrobenzene (as oxidant), hydrochloric acid and sodium hydroxide, ferric chloride is often used as catalyst, but sodium molybdate was substituted as a more effective catalyst. The materials were charged into a 4.5 m3 reactor and heating was started after addition of nitrobenzene, but the temperature controller was mis-set, and overheating at a high rate ensued. The exotherm was much higher than normal because of the more effective catalyst, and partial failure of the cooling water led to an uncontrollable exotherm. 

In the preparation of a dyestuff from aniline, nitrobenzene (as oxidant), hydrochloric acid and sodium hydroxide, ferric chloride is often used as catalyst, but sodium molybdate was substituted as a more effective catalyst. The materials were charged... 

The preparative application of nitrobenzene as oxidant is inconvenient, and a better agent is elemental sulphur. Taken in an equimolar amount to diamine 18, 29, 40 and 48 and aldehyde sulphur smoothly oxidized the intermediate IP dihydro derivatives to 2-aryl-IPs (54, 56, 57, 61, 62, and 58-66) with yields within 76-93%. The reaction occurred on fusion of the three components at 165-175 °C or on heating them in xylene until the end of hydrogen sulphide evolution. In both cases, only the target product, i.e. 2-aryl-IP, remained in the mixture with xylene solvent when the reaction was carried out by the second procedure (77SUP566842, 87KG639). 

Nitrobenzene as oxidant added dropwise at 150-155° during 15 min. to a soln. of 2-pyridinemethanol, aniline, and KOH in xylene, vigorous stirring continued 1 hr. at 170-175° with separation of the resulting water in a Dean-Stark trap N-(2-pyridylmethylene)aniline. Y 62.1% based on 2-pyridinemethanol. F. e. s. S. Miyano, N. and A. Abe, Chem. Pharm. Bull. 18, 511 (1970). 

Nitronium salts are capable to induce the OCA reaction via generation of aryl radical-cations, even with relatively electron-poor arenes, such as benzene [105]. Namely, NOBF4 in catalytic amount (1-5 mol%) efficiently catalysed the oxidative coupling reactions of polyalkoxybenzenes in dichloromethane (containing 20% trifluoroacetic acid) under exposure to air affording the corresponding biaryls in almost quantitative yields [105]. Finally, oxidative couplings of arenes can be accomplished under the classical Scholl reaction conditions [106]. For example, 1-ethoxynaphthalene (419) was coupled to binaphthyl 420 by reaction with anhydrous aluminum chloride and nitrobenzene (as oxidant) in 65% yield, Scheme 28. 

A soln. of Na2Gr207 in 30%-H2SO4 added during 15 min. to a suspension of 5,5 -dibromo-4,4 -dichlorindigo in 30%-H2SO4 containing an emulsifier active in acidic soln., heated to 80° and stirred 1 hr., if necessary with addition of nitrobenzene as oxidation-stable antifoam agent 5-bromo-4-chlorisatin. Y ca. E.Kambli, Helv. 47, 2155 (1964). 

Arsenic compounds could still be detected in the water after industrial practice had shifted to the use of nitrobenzene as oxidant in the production of magenta. These residues were the result of sulphuric acid production, as sulphurous non-ferrous ores usually contained arsenic. F. Fischer, Ueber die Verunreinigung der Fliisse durch Industrie- und stadtische Abfallstoffe und die Mittel dagegen . Dingier s Polytechnisches Journal, 211 (1874), 200-227, p. 202. Fischer calculated that 1,500,000 kg of arsenic per year were fed into rivers as a result of sulphuric acid production. 

The polyester domains of suberized walls can also be depolymerized using chemical and/or enzymatic approaches similar to those used for cutin. The aromatic domains are far more difficult to depolymerize as C-C and C-O-C crosslinks are probably present in such domains. Therefore, more drastic degradation procedures such as nitrobenzene, CuO oxidation, or thioglycolic... 

The addition of nitrobenzene into oxidized ester decreases the oxidation rate to some limit (v -> at [PhNOJ —> oo) [37]. Such a limitation of the retarding action occurs as a result of... 

The most important starting materials for process A are 4,4, 4"-triamino-triphenylmethane, pararosaniline (119), and parafuchsin (118). Aniline and formaldehyde are treated at 170°C to form, apart from some formaldehyde-aniline intermediates, 1,3,5-triphenylhexahydrotriazine as the main component. Subsequent treatment with an acidic catalyst, for instance with hydrochloric acid, in excess aniline as a solvent initially affords 4,4 -diaminodiphenylmethane, which is finally oxidized to yield parafuchsin (118). Iron(III)chloride and nitrobenzene, which in the past were used as oxidants, are no longer used. The reaction is now performed by air oxidation in the presence of vanadium pentoxide as a catalyst. 

Nitrobenzene oxidation was carried out by adding 50 mg of dry soda lignin into a mixture of 7 mL of 2 M NaOH and 4 ttiL of nitrobenzene in a 15 ttiL steel autoclave. Then, the antoclave was heated to 165°C for 3 hours in a preheated thermostat oil bath. After the autoclave was cooled to room temperature, the mixture was then transferred to a liqnid-hquid extractor for continuous extraction with chloroform (5 x 20 mL) in order to remove any nitrobenzene reduction product and excess nitrobenzene. The oxidation mixtnre was then acidified by concentrated HCl to pH 3 and further extracted with chloroform (5x15 mL). The solvent from the second chloroform solution was then removed using a rotary evaporator at 40°C under reduced pressure in order to obtain the nitrobenzene oxidation mixture. The mixture was then dissolved into dicloromethane and made up to 10 luL. This mixture was then used as a stock solution for high performance liquid chromatography (HPLC) analysis [6]. 

Figure 4.3 shows a representative voltarmnogram recorded at a three-phase electrode with a droplet configuration consisting of DMFC as a redox probe and nitrobenzene as the organic solvent. The oxidation of DMFC to decamethyUerrocenium cation... 

The three-phase electrode with a thin-film configuration (Fig. 4.2) has been mainly used in combination with nitrobenzene as an organic solvent and lutetium bis(tetra-i-butylphthalocyaninato) complexes as a redoxprobe (LBPC) [21,23]. Figure 4.5 depicts a typical voltammogram recorded with this redox probe in contact with 0.1 mol/L aqueous solution of KNO3. LBPC can be both oxidized and re-... 

It is apparent from Table IV that with nitrobenzene as the oxidation catalyst the ionization-limited rate was not reached even at a nitrobenzene concentration of 2.7M (0.02M fluorene, 0.02M potassium terf-butoxide). The rate of oxidation at the low nitrobenzene concentrations is first-order in nitrobenzene, fluorene, and base. This is consistent with an oxidation rate determined by Reaction 12 and involving an equilibrium concentration of the fluorene anions. 

Dr H. Sprengel, the inventor of vacuum pump, took out patents for a whole series of mining expls made by mixing together on the spot, just before the expl was required, an oxidizing substance with a combustible one. They were exploded by a fulminate detonator. As oxidizers he mentioned nitric acid and K chlorate and as combustibles carbon bisulfide, petroleum, Nitrobenzene, Nitronaphthalene and many other compds (Ref 11, p 43 Ref 12, p 7)... 

The excess negative charge located in the interior of metallic silver colloids could also be transferred to other electron acceptors, including methylviologen, nitrobenzene, nitropyridinium oxide, anthracene quinone sulfonic add, and potassium cyanohexaferrate(III)[506, 531], The efficiency and, indeed, the direction of electron transfer were found to depend on the position of the Fermi level of the surface-modified silver particles. For example, chemisorption of AgN to a silver particle is shown to result in a shift of the Fermi level to a more positive potential, as shown in the lower line in Fig. 84. 

For a better understanding of the factors that play a role in the catalytic selective reduction of nitrobenzene to nitrosobenzene some pieces of relevant information from previous work have to be considered. Favre et al.l6] found that oxides of various transition metals show catalytic activity in the mentioned reaction and a-Mn304 (Hausmannite) appeared to be the most active and selective catalyst. The function of nitrobenzene as an internal reducing agent has already been suggested by Zengell,] and is confirmed by Favre et al. Nitrobenzene can thus reduce as well as oxidize the catalyst... 

The reactivity of the nitro group is also manifested by the ease of its reduction. Thanks to this, aromatic compounds (e.g. nitrobenzene) can be used as oxidizing agents in the well known Skraup reaction. 

The glycerol was to provide acrolein (CH2=CH-CHO) by dehydration, the nitrobenzene was to act as oxidant, and the wide condenser... All too often Skraup reactions did let rip—with destructive results. A safer approach is to prepare the conjugate adduct first, cyclize it in acid solution, and then oxidize it with one of the reagents we described for pyridine synthesis, particularly quinones such as DDQ. 

Nitrosobenzene is readily synthesized by the chromic acid oxidation of /3-phenylhydroxylamine, which in turn is prepared by the reduction of nitrobenzene by the action of zinc dust and ammonium chloride (53%) The hydroxylamines need not be isolated. In other preparations, ferric chloride is employed as oxidant. ... 

Although these solvents should be electrochemically inactive over a wide potential range, this is not always the case since some solvents may be relatively easily reduced (e.g., nitrobenzene) or oxidized (e.g., amines). However, acetonitrile, which is frequently used in such studies, exhibits a very wide potential window from -t-3.4 to - 2.9 V vs. SCE [5] when tetrabutylammonium salts are used as background electrolytes. In acetonitrile and liquid SO2 as solvents, alkali metal cations could be oxidized [6] at an ultramicroelectrode, even to the divalent state. 

Sayari et al. [172,174] found that like their Ti containing analogs, V-HMS and V-MCM-41 are efficient catalysts for the hydroxylation of bulky aromatic molecules such as naphthol and 2,6 DTBP. Gontier et al. [186,237] found that V-HMS has no activity in the oxidation of aromatic amines in the presence of H2O2. However, it oxidizes aniline selectively into nitrobenzene when TBHP and acetonitrile are used as oxidant and solvent, respectively. Notice that Ti-HMS is active even in the presence of H2O2 and gives a different product distribution, particularly azoxybenzene [237], Das et al. [193] also reported that Sn-MCM-41 is effective in the liquid phase hydroxylation of phenol and naphthol. 

The oxidation of aniline was carried out in the liquid phase over a series of transition metal - substituted molecular sieves. For low oxidant/aniline ratios, azoxybenzene (AZY) was the major product formed over Ti-containing catalysts, the reaction was limited by diffusion for medium pore zeolites like TS-l and mesoporous silicas were preferred as they permitted the use of both H2O2 and tert-butyl hydroperoxide as oxidants. Higher oxidant/aniline ratios (>2) led to the formation of nitrobenzene (NB), whose selectivity was proportional to the catalyst concentration. In contrast, vanadium containing molecular sieves were only active with TBHP and aniline was converted very selectively into nitrobenzene for all oxidant concentrations. 

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