Benzidines, determination

Benzidine hydrochloride solution (for sulfate determination) mix 6.7 g of benzidine [Ci2H8(NH2)2] or 8.0 g of the hydrochloride [Ci2H8(NH2)2 2HC1] into a paste with 20 mL of water add 20 mL of HCl (sp. gr. 1.12) and dilute the mixture to 1 liter with water each mL of this solution is equivalent to 0.00357 g H2SO4. 

Titrimetric Methods. Frequently, the reduction of gold solutions leads to finely divided precipitates which are difficult to recover quantitatively. In such cases, the reduction of Au(III) to Au(0) by, eg, hydroquinone, can be followed potentiometricaHy (49). The end point in such titrations also can be determined with indicators such as benzidine (50) or o-anisidine (51). Alternatively, the reduction can be effected with excess hydroquinone which is then back-titrated with Ce(IV) (52). lodometric deterrnination of Au(III) also is useflil (53). 

SPEKTROPHOTOMETRIC DETERMINATION OF INDIUM BIS(2,3,4-TRIHYDROXYPHENILAZO)BENZIDINE IN PRESENCE PAPAVERINE, DIBAZOL, UROTROPIN... 

It is important for acid-catalysed reactions to determine whether the reaction is specifically catalysed by hydrogen ions or whether general acid catalysis takes place. Specific acid catalysis has been conclusively demonstrated for the benzidine rearrangement by three different sorts of kinetic experiments. In the first, it has been shown41 by the standard test for general acid catalysis (by measuring the rate of reaction in a buffered solution at constant pH over a range of concentration... 

Secondly, it has been found that the benzidine rearrangement is subject to a solvent isotope effect d2o/ h2o > 1- If a proton is transferred from the solvent to the substrate in a rate-determining step the substitution of protium by deuterium will lead to a retardation in the rate of reaction (primary isotope effect) whereas if a proton is transferred in a fast equilibrium step preceeding the rate-determining step as in... 

There is one further piece of kinetic evidence which throws light on an aspect of the benzidine rearrangement mechanism, and this is comparison of the rates of reaction of ring-deuterated substrates with the normal H compounds. If the final proton-loss from the benzene rings is in any way rate-determining then substitution of D for H would result in a primary isotope effect with kD < kH. This aspect has been examined in detail42 for two substrates, hydrazobenzene itself where second-order acid dependence is found and l,l -hydrazonaphthalene where the acid dependence is first-order. The results are given in Tables 2 and 3. 

Diaminobiphenyl is formed by a completely different mechanism, though the details are not known. There is rate-determining breaking of the N—N bond, but the C—C bond is not formed during this step. The formation of the o-semidine also takes place by a nonconcerted pathway. Under certain conditions, benzidine rearrangements have been found to go through radical cations. 

Cathodic stripping voltammetry has been used to determine down to 20 ng/1 selenium in seawater [542], The selenium is extracted with 3,3 diamino-benzidine and concentrated as HgSe on a mercury electrode at -0.45 V. 

The determination of neomycin by non-aqueous titration has been described by Penau et all2l. Neomycin base is allowed to react with standardised perchloric acid the excess acid is then back-titrated with potassium hydrogen phtha-late using crystal violet as indicator. To determine the neomycin content of the sulphate salt the same authors precipitated the sulphate with benzidine before reacting the neomycin with perchloric acid. The amount of benzidine required to precipitate the sulphate is calculated from the sulphate content which is itself determined by titration with sodium hydroxide. 

The most recent addition to Shine s extensive study of the benzidine-type rearrangements41 involved remeasuring the nitrogen and the carbon-13 and carbon-14 kinetic isotope effects at the 4- and at the 4- and 4 -carbons as well as determining the carbon-13 and carbon-14 isotope effects at the 1- and at the 1- and l -carbons in the benzidine rearrangement of hydrazobenzene (equation 30). The reaction, which was carried out in 75% aqueous ethanol that was 0.1 M in hydrochloric acid and 0.3 M in lithium chloride at 0°C, gave an 86% yield of benzidine (11) and a 14% yield of diphenyline (12). The kinetic isotope effects found for the formation of benzidine and diphenyline under these reaction conditions are presented in Table 5. 

Determination of Benzidines and Nitrogen-Containing Pesticides in Water by LLE or LSE and Reverse Phase... 

Determination of Certain Benzidines in Municipal and Industrial Discharges using LLE and HPLC... 

Riggin RM, Howard CC. 1979. Determination of benzidine, dichlorobenzidine, and diphenylhydrazine in aqueous media by high performance liquid chromatography. Anal Chem 51 210-214. 

Riggin RM, Howard CC. 1982. Determination of benzidines in industrial and municipal wastewaters. 

Dichlorobenzidine was found to be extremely photolabile in water (Sikka et al. 1978 Banerjee et al. 1978). 3,3 -Dichlorobenzidine photolyzed yielding monoehlorobenzidine, benzidine, and a number of eolored, water-insoluble products. In natural sunlight, the half-life of 3,3 -dichlorobenzidine in water was determined to be approximately 90 seeonds. While 3,3 -diehlorobenzidine is very rapidly photolyzed rmder environmental conditions, the process may yield benzidine, a relatively photostable carcinogen (Banerjee et al. 1978). 

Armentrout DN, Cutie SS. 1980. Determination of benzidine and 3,3 -dichlorobenzidine in wastewater by liquid chromatography with UV and electrochemical detection. J Chromatogr Sci 18 370-374. 

Bowman MC, Rushing CR. 1981. Trace-level determination of benzidine, 3,3 -dichlorobenzidine in animal chow wastewater and human urine. In Egan H, ed. Environmental carcinogens - selected methods of analysis. Volmne 4. Some aromatic amines and azo dyes in the general and industrial environment. Lyon, France International Agency for Research on Cancer, 159-174. 

Kawahara FH, Dunn JR, Fiutem RA, et al. 1982. Determination of benzidines by gas chromatographic separation of derivatives with electron capture detection. Anal Chim Acta 138 207-220. 

Riggin RM, Howard CC, Scott DR, et al. 1983. Determination of benzidine related congeners and pigments in atmospheric particulate matter. J Chromatogr 21 321-325. 

Susceptibility to bladder cancer in humans has been linked to the slow acetylator phenotype of the polymorphic NAT2 AT-acetyltrans-ferase gene. In a study from China, a 25-fold increase in bladder cancer incidence and a 17-fold increase in bladder cancer mortality were determined in 1972 benzidine-exposed workers. In the Asian population the slow acetylator phenotype occurs significantly less often than in Caucasian populations, but an association between those who contracted bladder cancer and phenotype has yet to be determined for this group. Other, more recent data have suggested that the acetylation rate may not be an important risk factor for developing bladder cancer. ... 

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