Benzidine sulphate

Other reagents which may be applied to the volumetric determination of sulphuric acid and sulphates are barium chromate and benzidine. In the case of the former, the solution of sulphate is precipitated by a solution of barium chromate in hydrochloric acid on subsequent neutralisation of the filtrate, a quantity of chromic acid, equivalent to the barium sulphate which has been precipitated, remains in solution and may be estimated iodometrically.6 Benzidine, on the other hand, is an organic base which forms a very sparingly soluble sulphate the solution of mineral sulphate is treated with a solution of benzidine hydrochloride and the precipitated benzidine sulphate removed by filtration when subsequently suspended in pure water the benzidine sulphate undergoes hydrolysis to a sufficient extent to permit titration of the sulphuric acid with standard alkali.7 Lead nitrate may also be... 

To 56 gms. of pure benzidine sulphate 600 gms. of pure cone, sulphuric acid are added and the mixture well stirred. Solution is completed by... 

Benzidine.—It is then removed to a basin where it is boiled up slowly with 500 c.cs. water and 120 c.cs. cone, hydrochloric acid and filtered from sine residue. A saturated solution of sodium sulphate is then added until the benzidine sulphate is completely precipitated (test). This is filtered off and is well washed with warm water until free of acid. The moist benzidine sulphate is removed, heated to 50° with a little water, and caustic soda solution (30%) added with stirring until the liquid is just alkaline (test with phenolphthalein). When cold, the free base is filtered off and dried at 50°. It may be crystallised from benzene, alcohol or from hot water (see p. 498). 

Haussermann 2 reduced nitrobenzene and nitrotoluenes both in alkaline and acid solution, the former with iron, the latter with platinum, electrodes. By reduction in alkaline solution, he obtained as principal product hydrazobenzene and hydrazo-toluene respectively in sulphuric-acid solution he got from nitrobenzene, as chief products, benzidine sulphate and azoxy-benzene, besides an easily changeable body which was not further determined. o-Nitrotoluene3 under like conditions gave o-tolui-dine sulphate besides small quantities of o-toluidine p-nitro-toluene yielded principally p-toluidine. 

Benzidine hydrochloride solution white precipitate of benzidine sulphate. (DANGER THE REAGENT IS CARCINOGENIC.)... 

BENZIDINEDICARBOXYUC ACID see BFX250 BENZIDINE HYDROCHLORIDE see BBX750 BENZIDINE SULFATE see BBYOOO BENZIDINE SULPHATE and HYDRAZINE-BENZENE... 

Experiment Hydrazobenzene is covered with concentrated hydrochloric acid, and allowed to stand for about 5 minutes. It is then treated with water, and half the solution is made alkaline with caustic soda the free benzidine is extracted several times with ether, the ether evaporated, and the substance crystallised from hot water. Leaflets of a silvery lustre are obtained. Melting-point, 1220. The other half of the solution is treated with dilute sulphuric acid, upon which the difficultly soluble benzidine sulphate separates out... 

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. 

IARC. 1982a. Benzidine and its sulphate, hydrochloride and dihydrochloride. International Agency for Research on Cancer. lARC monographs Lyon, France 29 151-183. 

Aldehydes. Common impurities found in aldehydes are the corresponding alcohols, aldols and water from selfcondensation, and the conesponding acids formed by autoxidation. Acids can be removed by shaking with aqueous 10% sodium bicarbonate solution. The organic liquid is then washed with water. It is dried with sodium sulphate or magnesium sulphate and then fractionally distilled. Water soluble aldehydes must be dissolved in a suitable solvent such as ethyl ether before being washed in this way. Further purification can be effected via the bisulphite derivative (see p. 51) or the Schiff base formed with aniline or benzidine. Solid aldehydes can be dissolved in ethyl ether and purified as above. Alternatively, they can be steam distilled, then sublimed and crystallised from toluene or petroleum ether. 

Sulphur and Sulphates.—Thoroughly mix 5 gm. of benzidine with a mixture of 5 gm. of anhydrous sodium carbonate... 

This work was extended by Elbs and his pupils,1 and the processes were protected by patents.2 Subsequently alcohol was dispensed with and aqueous caustic soda employed. For example, an emulsion of nitrobenzene in 10 per cent, aqueous sodium hydroxide may be reduced with a cathode of lead or nickel in a porous earthenware cell, with a current density of 10-12 amps, per dm.2 An anode of graphite or lead may be employed in an outer containing vessel filled with sodium hydroxide solution or sodium sulphate. Azo- or hydrazobenzene is obtained according to the quantity of electricity passed through, and the azobenzene emulsion can be transformed into benzidine by acidifying the cathode liquor and completing the reduction.4... 

We will have to suppose that the lead sponge occurring at the lead cathode reduces the nitrobenzene to aniline. Men-tionable quantities of lead sulphate cannot be found, since this is continually reconverted to lead sponge by the freed hydrogen ions. This process is analogous to the one previously published by me3 in which a hydro-alcoholic solution of nitrobenzene acidified with sulphuric acid gives aniline when a zinc cathode is used. Considerable quantities of zinc sulphate do not occur. At a platinum cathode, under the same conditions, no aniline is formed, but azoxybenzene and hydrazobenzene or benzidine form. This has been confirmed by Haussermann. 4... 

A different type of diarsinie acid is fonned by treating diazotised benzidine or its derivatives with sodium arsenite in the presence of copper sulphate. Benzidine itself yields diphenyt-ii 4> -diarsinic add. 

Sensitive indirect methods are based on precipitation of sulphate ions with benzidine or 4-amino-4 -chlorobiphenyl (e = 5.5-10 at 480 nm), and obtaining suitable azo dyes [50,51],... 

Benzidine is formed directly by reducing azobenzene in acid solution. The structure of the amine has been shown to be that indicated, by converting it into diphenyl. The amino groups may be replaced by hydrogen by the method outlined in the case of nitrotoluidine (499). Benzidine crystallizes in colorlesSj silky plates, which melt at 122°. It is characterized by its solubility in hot water, and the sparing solubility of its sulphate. It is used in large quantities in the manufacture of certain dyes. 

If ammonium molybdate is added to an acidified orthophosphate solution, followed by a reducing agent such as stannous chloride or ferrous sulphate, an intense blue colour ( molybdenum blue ) will develop. A more satisfactory and sensitive version of this test is to use benzidine as the reducing agent in which case an intense blue colour arises from both the molybdenum blue and a reduced product from the benzidine which is also blue. 

Cnprie sulphate-benzidine for pyridine monocarboxylic acids. 

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