4- diphenylamine, indicator

A second important group includes the diphenylamine indicators. In the presence of a strong oxidizing agent, diphenylamine is irreversibly converted to diphenylbenzidine. This latter compound undergoes a reversible redox reaction accompanied by a colour change,... 

Assay Transfer about 170 mg of sample, previously ground to a fine powder and accurately weighed, into a 250-mL wide-mouth Erlenmeyer flask, and dissolve in 10 mL of methanol. Add 150 mL of water, 1 mL of 1 N sulfuric acid, and 4 drops of diphenylamine indicator (3 mg of / -di phenyl ami ncsu I Ionic acid sodium salt per milliliter of 0.1 N sulfuric acid), and titrate with 0.1 N ceric sulfate to the first complete color change from yellow to red-violet. Record the volume, in milliliters, of 0.1 N ceric sulfate required as V. Calculate the percentage of C10H14O2 in the sample, uncorrected for hydroquinone and 2,5-di-tm-butylhydroquinone, by the formula... 

Eu K2Cr207 Reduction with Jones reductor, FeClj added, diphenylamine indicator [96]... 

FeS04(NH4)2 SO4. I2H2O + H2SO4 + O Action of diphenylamine indicator... 

Diphenylamine indicator-. Dissolve 0.5 g of diphenylamine in a mixture of 100 ml cone, sulphuric acid and 20 ml distilled water, and store in a coloured bottle. 

Add 200 ml of distilled water, 10 ml of orthophosphoric acid and 1ml of diphenylamine indicator. A blue violet colour will appear. 

In view of the diversity of medium effects between water and dimethylsulphoxide, we must expect any acidity function that is anchored to the pH scale in water to apply only to acids with very similar structures. Dolman and Stewart have reported values of the H acidity function in dimethylsulphoxide-water mixtures based on 24 substituted aniline and diphenylamine indicators. Dimethylsulphoxide containing 0.4 mol per cent water has a H value of 26.2. 

Weigh out accurately about 0.5 g of your preparation, add about 50 cm of dilute sulphuric acid and place in a Buchner flask, whose rubber bung carries a burette containing standard potassium dichromate solution (about 0.0167 M). Add a few drops of diphenylamine indicator, apply suction and titrate under the reduced pressure until the colour changes to violet. Repeat the determination and determine the percentage purity of your preparation. 

Titration curve for 50.00 ml of 0.0500 M Fe + with 0.0500 M Ce + showing the range of f and volume of titrant over which the indicators ferroin and diphenylamine sulfonic acid are expected to change color. 

Mention should be made of one of the earliest internal indicators. This is a 1 per cent solution of diphenylamine in concentrated sulphuric acid, and was introduced for the titration of iron(II) with potassium dichromate solution. An intense blue-violet coloration is produced at the end point. The addition of phosphoric(V) acid is desirable, for it lowers the formal potential of the Fe(III)-Fe(II) system so that the equivalence point potential coincides more nearly with that of the indicator. The action of diphenylamine (I) as an indicator depends upon its oxidation first into colourless diphenylbenzidine (II), which is the real indicator and is reversibly further oxidised to diphenylbenzidine violet (III). Diphenylbenzidine violet undergoes further oxidation if it is allowed to stand with excess of dichromate solution this further oxidation is irreversible, and red or yellow products of unknown composition are produced. 

For the titration of colourless or slightly coloured solutions, the use of an indicator is unnecessary, since as little as 0.01 mL of 0.02 M potassium permanganate imparts a pale-pink colour to 100 mL of water. The intensity of the colour in dilute solutions may be enhanced, if desired, by the addition of a redox indicator (such as sodium diphenylamine sulphonate, AT-phenylanthranilic acid, or ferroin) just before the end point of the reaction this is usually not required, but is advantageous if more dilute solutions of permanganate are used. 

The green colour due to the Cr3+ ions formed by the reduction of potassium dichromate makes it impossible to ascertain the end-point of a dichromate titration by simple visual inspection of the solution and so a redox indicator must be employed which gives a strong and unmistakable colour change this procedure has rendered obsolete the external indicator method which was formerly widely used. Suitable indicators for use with dichromate titrations include AT-phenylanthranilic acid (0.1 per cent solution in 0.005M NaOH) and sodium diphenylamine sulphonate (0.2 per cent aqueous solution) the latter must be used in presence of phosphoric) V) acid. 

Experimentally, the molecular geometry has been determined by X-ray analysis for several larger radicals. These data indicate, in agreement with the theory, that bond alternation characteristic in many reduced and oxidized closed-shell forms is diminished in radical ions. Precise crystallographic data are available for 4,4 -A/s(dimethylamino)diphenylamine radical cation (87, 88), N,N -diphenyl-p-phenylenediamine radical cation (89), and Wiirster s blue (90). 

The use of a sulphonic acid derivative of diphenylamine overcomes the problem of low indicator solubility. 

Steric effects on the nucleophile, aniline, were clearly evident. Rate constants for bimolecular attack of 2,6-dimethyl- 70a, 2,6-diethyl- 70b, and 3,5-dimethylaniline 70c at 308 K indicate that the ort/zo-substituted anilines react more than an order of magnitude slower at the same temperature (Table 7). Structure 70c must be able approach the reactive nitrogen more closely.42,43 A comparison of the rate constants for reaction of aniline 72c, /V-methyl- 71a and /V-phenylaniline 71b provides further evidence of steric effects although the very small rate constant for the diphenylamine could also be accounted for by reduced nucleophilicity on account of lone pair resonance into the additional phenyl ring. 

Potassium dichromate exhibits much greater stability in aqueous solution in comparison to potassium permanganate. Potassium dichromate possesses an inherent oranage colour that is not intense enough to serve its own end-point signal, specifically in the presence of the green Cr3+ ion, which is supposed to be present at the end-point. Hence, redox indicators are usually employed to locate the exact end-point e.g., barium diphenylamine sulphonate. 

Due to the high interest in metalation reactions with lithium amide or alkyllithiums, an indicator scale of lithium ion pairs in THF has been developed119. Aggregation studies have indicated that organolithium species exist predominantly, if not exclusively, as monomers in the 10-3-10-4 M concentration range. Particular attention has been devoted to the lithium and caesium ion-pair acidities of diphenylamine in THF120 that, at 25 °C, have been found to be 19.05 and 24.20, respectively. 

A single report of skin sensitization indicates that diphenylamine could be a skin sensitizer in humans. It is slightly irritating to rabbit skin and moderately to severely irritating in rabbit eyes. ... 

Elemental composition K 28.22%, Cl 25.59%, and 0 46.19%. An aqueous solution is analyzed for potassium by AA, ICP, and other methods (see Potassium). Perchlorate ion may be analyzed by ion chromatography or a liquid-membrane electrode. Iodide, bromide, chlorate, and cyanide ions interfere in the electrode measurement. Alternatively, perchlorate ion may be measured by redox titration. Its solution in 0.5M H2SO4 is treated with a measured excess standard ferrous ammonium sulfate. The excess iron(II) solution is immediately titrated with a standard solution of potassium dichromate. Diphenylamine sulfuric acid may be used as an indicator to detect the end point ... 

Cautiously add, with stirring, 15 ml of. sulfuric acid, 5 ml of phosphoric acid, and 6 to 8 drops of Na diphenylamine sulfonate indicator soln (0.2g/100 ml of w). Titrate slowly with 0.05N std K dichromate soln until the pure grn color changes to a gray-green. Then add the dichromate one drop at a time until the first tinge of purple or violet-blue appears... 

Jacque Stability Test. Jacque, director of the Spanish plant Cantabrica at Guldacano, near Bilbao, proposed a test for NC which was simple, rapid, and did not require complicated apparatus. It is not advisable to use this test when it is known in advance that the NC is of low stability Procedure. A NC sample of 2-3g, previously-dried in a loosely covered weighing dish or crystallizer to constant wt, is transferred to an oven maintained at 130—40° and left there for 2 hrs. It is cooled in a vacuum desiccator and reweighed. The sample is again heated at 140° and weighed at intervals of 2 hrs until it decomposes, as indicated by an abnormal loss of wt. After termination of the test, it is advisable to wash the NC with distilled water, add a few drops of 0. IN KMn04 soln and determine the amt of HN03, either by the nitron or diphenylamine method... 

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