Benzidine conversion

Good agitation is essential, and a solvent may be used in some cases. This, however, is not always necessary if the agitation is efficient. The compounds are isolated by dissolving out the zinc with ice-cold hydrochloric acid. The hydrazo compounds, when heated with mineral acids, undergo a rearrangement (benzidine conversion). 

Better yields of azo and hydrazo compounds are sometimes obtained by reducing the azoxy compound in preference to the nitro compound. Certain hydrazo compounds, e.g., hydrazo-naphthalenes, undergo the benzidine conversion (see p. 160) in alkaline as well as in neutral solution, so that the product finally isolated in the reduction is a diamino base. (J. C. S., 125, 1108.)... 

The conversion of a hydrazobenzene into a diaminodiphenyl upon treatment with acid is termed the benzidine rearrangement. The following mechanism for the formation of benzidine from hydrazobenzene appears reasonable ... 

Horseradish peroxidase (HRP) an enzyme routinely used in immunohisto-chemistry for labeling antibodies. Histochemichal detection of peroxidase is based on the conversion of aromatic phenols or amines, such as diamino-benzidine (DAB), into water-insoluble pigments in the presence of hydrogen peroxide (H202). 

The conversion of hydrazobenzene into the isomeric benzidine— discovered by the Russian chemist Zinin in the year 1846—is started catalyticaUy by mineral acids and results from the tendency of the molecule to pass into a form possessing less energy, i.e. into a more saturated condition. The reaction is suitably classified with those of which the chief characteristic is that a substituent united to nitrogen exchanges its point of attachment with an H-atom of the nucleus— usually an H-atom in the p-position. To this class belong the conversion of phenylsulphaminic acid into sulphanilic acid (p. 198), of phenyl-hydroxylamine into p-aminophenol (p. 176), and also of acetanilide into p-aminoacetophenone and of N-chloroacetanilide into p-chloro-acetanilide ... 

Waste water Extraction, conversion of 3,3 -dichloro-benzidine to pentafluoropropionamides. HPLC/EC 0.2 pg Kawahara et al. 1982 ... 

Hydrazobenzene, 628, 629, 632 conversion into benzidine, 633 Hydrazo compounds, 1074 table of, 1085 ... 

Type E1 D-+E1 Synthesis. Dyes of this type require the conversion of an aryldiamine to a tetrazonium compound (one that has two diazonium groups), in a process know as tetra-zotization. See Fig. 13.93, which involves environmentally friendly alternatives to benzidine. Following tetrazotization, one tetrazonium molecule reacts with two coupler molecules to produce the target dye, examples of which are provided in Fig. 13.94 (11 C.I. Direct Red 28 (Congo Red), 12 C.I. Direct Yellow 12, and 13 C.I. Acid Yellow 42). Disazo dyes prepared this way include dye 14 (C.I. Direct Blue 15), which is converted to the important bis-copper complex, C.I. Direct Blue 218 (see Fig. 13.95). 

Nickel(II) hydroxide test The auto-oxidation of sulphur dioxide (or sulphurous acid) induces the oxidation of green nickel(II) hydroxide to the black nickel(III) hydroxide. The colour change is quite distinct, but for very small amounts of sulphur dioxide use may be made of the conversion of benzidine acetate to benzidine blue by the nickel(III) hydroxide. (DANGER THE REAGENT IS CARCINOGENIC.) Thiosulphates give a similar reaction and must therefore be absent sulphides also interfere. 

The spot-test technique of the reaction utilizes the conversion of the silicic and fluosilicic acids by means of ammonium molybdate into silicomolybdic acid H4[SiMo12O40]. The latter, unlike free molybdic acid, oxidizes benzidine in acetic acid solution to a blue dyestuff and molybdenum blue is simultaneously produced. (DANGER THE REAGENT IS CARCINOGENIC.)... 

Little work has been published concerning the isolation of oligosaccharides following graded, acidic hydrolysis of heparin. Wolfrom and co-workers have studied the partial, acid hydrolysis of a carefully purified heparin. (Purification was effected through the benzidine salt and the neutral barium salt was fractionally precipitated from water. The less-soluble fraction, after conversion to the barium acid salt, had a N S ratio of 2 5 and 5 sulfate groups per tetrasaccharide period, consumed 1 mole of periodate per tetrasaccharide period, and was shown to be homogeneous by electrophoresis and by countercurrent distribution. The molecular... 

The reduction of azoxy benzene to hydrazobenzene is of preparative interest [132,134], due to the easy conversion of hydrazobenzenes to benzidines and similar compounds. Several patents [177] describe the conversion of nitrobenzene to azoxybenzene and further to hydrazobenzene environmental considerations are in favor of the electrochemical reduction compared with the metal powder reductions, and the method stands a good chance to be competitive in the future. 

An interesting reaction that represents a half-way point between the quinamine and benzidine rearrangements can be also mentioned here129, namely the conversion of A-acetyl-0,A-diphenylhydroxylamine 78 into biphenyls 79 and 80 (equation 32) (see Section IILA.4.C about rearrangements of A-acylanilines and Section m.C.l concerning rearrangements of hydroxylamines). 

The arenesulfenanilide rearrangement is another member of an important class of rearrangements described above, such as the benzidine, quinamine and nitramine rearrangements. This rearrangement consists of the conversion of arenesulfenanilides 197 into ortho- and para-aminodiphenyl sulfides 198 and 199287.288 (equation 76). Substitution at the para-position generally predominates over ortho-substitution289. 

From the standpoint of switchable properties it would be desirable to build a rotaxane capable of more sharply defined on-off conversions. Before switching, rotaxane 24+ presents two translational conformers, characterized by either benzidine or biphenol occupation by the bead. Although benzidine occupation is heavily favored (84% vs. 16%), the fraction of systems that show biphenol occupation are conceptually equivalent to a leak in the switching device. The selectivity of the bead for one of the two donor stations can be accomplished by one of two approaches ... 

Benzidine rearrangements in the thiazole series- have been described by Beyer and Kreutzberger,89 but they are successfullonly if the diamine produced is trapped by conversion into the phthaloylamino compound by reaction with phthalic anhydride ... 

An interesting ort/io-aminophenylation reaction of reactive heterocycles is exemplified by the conversion of 4-chloro-3-nitropyridine (39) into the o-aminophenyOpyridone (40). The ortho-ortho-lmked product contrasts with the previously discovered reaction of 2-chloro-3-nitropyridine, which, under the same conditions, gives a para-para- inked product. This very rare ortho-ortho benzidine-type rearrangement only occurs when a para-position is blocked, and has also been carried out with appropriately substituted pyrimidine and benzene derivatives (Scheme 18). 

Difficulties of this sort have been reported, e.g., in the extraction of phenols which had been converted to azo dyes on the adsorbent layer [623]. The reaction of sulphonamides with a diazonium reagent has been taken to completion by adding excess reagent again after having extracted the coloured product [69]. The determination of monosaccharides with benzidine-glacial acetic acid has been carried out similarly [38]. The method has been used also for the quantitative analysis of amino acids, after colour reaction with ninhydrin [42, 95] corticosteroids, after reaction yielding formazans [64] and of cannabinols after conversion into azo compounds [370]. 

Test with benzidine, o-dianisidine or 2,7-diaminodiphenylene oxide after conversion into chromate ... 

When thallium is present in the Tl state, it can be detected, after conversion into TIO(OH), by the oxidation of benzidine to benzidine blue (see page 283). Thallous salts must be oxidized beforehand. This is accomplished by means of potassium ferricyanide in alkaline solution... 

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