Azoxybenzene, determination

Azobenzene, determination of 263, 264 Azo dyes, determination of 188 Azoxybenzene, determination of 263, 264... 

Many organic chemicals are analyzed by RPC. These include various arylhydroxylamines as the N-hydroxyurea derivative with methyl isocyanate (614) alkyl- and alkoxy-disubstituted azoxybenzenes (6t5), n-alkyl-4-nitrophenylcarbonate esters ranging in length from methyl to octyl (616), 4-nitrophenol in the presence of 4-nitrophenyl phosphate (617), ben-zilic acid, and benactyzine-HCI using ion-pair chromatography (618), as well as aniline and its various metabolites (619), stereoisomers of 4,4 -dihydroxyhydrobenzoin (620), and aldehydes and ketones as the 2,4-dinitrophenylhydrazones (621). The technique has also been used to analyze propellants and hydrazine and 1,1-dimethylhydrazine were quantitita-vely determined (622, 623). 

Azoxybenzene is moderately endothermic (AEtf (s) +152.3 kJ/mol, 0.77 kJ/g). (The isolated stereoisomeric components [21650-65-7] tcis-, [20972-43-4] itrans-may differ significantly from these values) [1], Energy of decomposition in range 245—420°C measured by DSC as 1.303 kJ/g by DSC, and Tait24 was determined as 191°C by adiabatic Dewar tests, with an apparent energy of activation of 194 kJ/mol [2],... 

The number of photons absorbed was determined using a commercially-available electronically integrating actinometer (QuantaCount, PTI, Deer Park N J.), which was calibrated using azoxybenzene (6). Solutions of I (3.0 mL, 0.01 M) were irradiated with monochromatic light (325 nm) in a long-necked quartz cell, lxl cm2. The cells... 

A thin layer chromatographic method has been developed [117] for the determination of organic compounds capable of cis-trans isomerisation, using dibutyl ethylenedicarboxylate, stilbenzene, azobenzene and azoxybenzene as examples. The civ-isomers were formed from the trans by irradiating solutions with ultraviolet light. For chromatography, plates with a layer of silica gel fixed with gypsum and plates with a... 

In the reduction of nitrobenzene in a 2% aqueous sodium-hydroxide solution, according to previous publications, azoxy-benzene is formed at platinum and nickel electrodes, azobenzeno at lead, tin, and zinc cathodes, and aniline at copper cathodes especially in the presence of copper powder. It was found that, in an unchangeable experimental arrangement, a cathodo potential of 1.8 volts, as measured in connection with the deci-normal electrode, could be carried out with all the chosen cathodes and additions. At this constant potential, by using different metals and adding various metallic hydroxides, the whole reduction was carried out and the nature and quantity of the reduction products determined in each case. It turned out that the emphasized differences in the results disappeared and that, with an equal potential of all cathodes, similar yields of azoxybenzene and aniline and traces of azobenzene resulted. The cathodes were of platinum, copper, copper and copper powder, tin, platinum with addition of stannous hydroxide zinc, platinum with addition of zinc hydroxide, lead, platinum with addition of lead hydroxide, and nickel. The yields of azoxybenzene varied from 41-65% of aniline 23-53%. 

The nature of the electrolyte sometimes has an important influence on the products of electrolytic reduction. The alkalinity or acidity, for example, plays an essential part in determining the nature of the substance obtained in the reduction of nitrobenzene in this case the effect is mainly due to the influence of the hydrogen ion concentration on various possible side reactions. The formation of azoxybenzene, for example, in an alkaline electrolyte is due to the reaction between phenyl-hydroxylamine and nitrosobenzene, viz.,... 

While determining the scope of the synthetic utility of urea-hydrogen peroxide in oxidation reactions, it was observed that aniline can be converted to azobenzene and azoxybenzene in good yield, as shown in Fig. 2.8. 

A kinetic stndy of this reaction in media of different acid concentrations (Buncel, 2000) gave the resnlts shown in Table 3.5, which records as well the corresponding X and // valnes. Also given in Table 3.5 are the extents of protonation of azoxybenzene, according to Eqnation B, which are calculated (Buncel, 1975a, b) from the spectrophotometrically determined value, p/f =-5.15, corresponding to 50% protonation of azoxybenzene in 65% H SO (Hg=-5.15). From these resnlts, what can yon deduce about the role of protonation of 1 in its ease of rearrangement and hence on the mechanism of Reaction A ... 

Cu-Ni alloys. The equipment works up to 700 MPa. The pressure transmitting medium was purified helium gas. The NMR coil and the sample are contained inside a heating tube. The N-I and the Cr-N transitions of 4,4 -bis-methoxy-azoxybenzene were observed up to 400 MPa and 210 °C. The order parameter of the nematic phase could be determined from a characteristic doublet of the NMR CW spectrum. The order parameter at the N-I transition is found to be constant up to 300 MPa. 

One of the most striking anisotropic properties of nematic liquid crystals is their optical anisotropy, which is manifested as birefringence. It was this property of liquid crystals that led to their discovery about 100 years ago, and early in the history of liquid crystals attempts were made to determine their birefringence. The first rough estimation was made by Lehmann in 1905 [1], who placed the nematic phase of 4,4 -bis(methoxy)azoxybenzene between a plane glass plate and a lens with a large radius of curvature. The birefringence... 

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