Determination of nitrobenzene in aniline

Aniline usually contains traces of nitrobenzene which can be determined polarographically. 

Procedure. Prepare a buffer solution (pH 7) by dissolving 3.7 g pure citric acid and 23.6 g of potassium dihydrogenphosphate in 1 L of distilled water. 

Prepare a stock solution of nitrobenzene by dissolving about 0.25 g (accurately weighed in a weighing bottle) in 50 mL of 95 per cent ethanol, and adding this to 450 mL of the buffer solution contained in a 500 mL graduated flask. Rinse the weighing bottle with two successive 5mL portions of 95 per cent ethanol and add each rinsing to the 500 mL flask finally make the flask up to the mark with buffer solution. 

Finally, determine the polarogram of the aniline solution, and from the wave height deduce the nitrobenzene content of the sample E1/2 ca —0.4 V. 

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Thallous Azidodithiocarbonate A637-L Thallous-Thallic Azide A623-R Thermonuclear or Fusion Bomb. See under Atomic Bomb A499-L Thorium Dicarbide A82-R Tin Azide A624-L Titanium Carbide A82-R Titanous Chloride Method for Determination of Nitrobenzene in Aniline A415-R TNT Recovery from Scrap Amatol A161-L Toluidine. See under Aminotoluenes A265-R... 

If the sample does not contain more than two (or three) NOa groups, the titanous chloride method(described above under detn of nitrobenzene in aniline) may be applicable. This method determines the nitro-nkrogen but not the amino-nitrogen. No info is available on application of the TiCl3 method to tri-, tetra- and pentanitroanilines, but it definitely works with mono- and di-nitro derivs... 

Nitrocompounds, Polarography was successfully used for the determination of traces (to 0 0001 per cent) of nitrobenzene in aniline... 

A comparison of active (using pumps) and passive (relying on diffusion) sampling techniques for the determination of nitrobenzene, benzene and aniline in air was mentioned in Section IV.A77. Several LLE methods for nitroaromatic compounds dissolved in water were evaluated. High recoveries were achieved with discontinuous or continuous extraction with dichloromethane, adsorption on a 1 1 1 mixture of Amberlite XAD-2, -4 and -8 resins and elution with dichloromethane445. 

In presence of morpholine, (17) catalyzes the hydrogenation of nitrobenzene to aniline.61 A near twofold excess of the amine relative to (17) was used. At a higher excess, catalysis ceased. This was attributed to formation of a bis-morpholine complex. The hydrogenation proceeds best in solvents such as acetone, ethyl acetate or THF.62 The transfer of the first hydrogen atom to nitrobenzene was found to be rate determining and a dinuclear nitrobenzene complex (18) was postulated. The base (B) is morpholine. 

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 reduction rates of nitrobenzene to aniline using a Magen reactor have been determined with platinum-Neobead C-1 catalysts which differ in/from... 

Organic polarography is extensively used for the determination of compounds of industrial and agricultural interest (particularly for process and quality control). A classic example is the determination of trace impurities (0.001-0.1%) of nitrobenzene in technical-grade aniline. 

The catalytic system Ru3(CO)i2/DIAN-Me, (see Chapter 4.2.3. for a drawing of DIAN-Me) is one of the most active catalysts for the reduction of nitrobenzene to aniline by CO/H2O (see Chapter 4.2.3.) [101], The conditions described in Scheme 22 gave conversions of 100 % of the starting material. The relative amounts of 64 and 65 were determined by H NMR and the only other product isolated in significant amount was the corresponding 2 -aminochalcone (66). Treatment of the reaction mixture 64/65b or h with 2,3-dichloro-5,6-dicyano-/> ra-benzoquinone at 60 °C allowed the selective s> nthesis of the quinolones 64. In the case of the substrates 63b and 63h, reduction of the reaction time to 1 h also gave the corresponding 2 -aminochalcones (66). 

Organic substances may be determined either in an aqueous or a nonaqueous medium. For example, the concentration of nitrobenzene in commercial aniline may be found by studying the reaction ... 

Hydrogenation of Nitrobenzene. In a three-necked flask, 0.21 mL (2 mmol) of nitrobenzene, 5 mL of methanol, and 7.1 mg (0.02 mmol/Pd) of Pd-Gr were added under hydrogen atmosphere. The mixture was stirred at room temperature and the hydrogen consumption was monitored by using a gas buret. The yield of aniline formed was determined by GC measurements without isolation. 

Variations in retention and selectivity have been studied in cyano, phenyl, and octyl reversed bonded phase HPLC columns. The retention of toluene, phenol, aniline, and nitrobenzene in these columns has been measured using binary mixtures of water and methanol, acetonitrile, or tetrahydrofuran mobile phases in order to determine the relative contributions of proton donor-proton acceptor and dipole-dipole interactions in the retention process. Retention and selectivity in these columns were correlated with polar group selectivities of mobile-phase organic modifiers and the polarity of the bonded stationary phases. In spite of the prominent role of bonded phase volume and residual silanols in the retention process, each column exhibited some unique selectivities when used with different organic modifiers [84],... 

Water was used as the catalyst phase for the palladiiun complex of TPPTS and toluene or an excess of the substrate anihne served as the non-polar product phase. To determine an appropriate solvent system cloud titrations were performed at 90 °C, 60 °C, 40 °C and 25 °C. A solution of 4-chloro-nitroben-zene in aniline and water were mixed in a weight ratio of 1 1 and semi-polar solvents were added as a mediator until a homogeneous solution was formed. As the mediator the following solvents were apphed methanol, ethanol, isopropyl alcohol, n-butanol, DMF, DMSO, ethylene glycol, N-methylpyrrohdone (NMP), 1.4-dioxane and acetonitrile. The cloud titrations were repeated whereby the substrate 4-chloro-nitrobenzene was replaced with the product 4-nitrodiphenylamine. In all cases more of the semi-polar mediator is required for the product mixture at 25 °C than for the reaction mixture at 60 °C to obtain a clear solution. 

Patil SF, Lonkar ST. 1992. Thermal desorption-gas chromatography for the determination of benzene, aniline, nitrobenzene and chlorobenzene in workplace air [published erratum appears in J Chromatogr 1992 Nov 20 625(2) 402], J Chromatogr 600(2) 344-351. 

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