Diphenylamine blue

Unsubstituted polysaccharides do not appreciably absorb ultraviolet and visible radiation, but they can be made to do so intensely by combining them with chromophores and chromogens (e.g., a-naphthol, dihydroxynaph-thalein, anthrone, carbazole, phenol-sulfuric acid, 2-thiobarbituric acid, tolu-idine blue, diphenylamine, Congo red, aniline blue, and methyl orange), usually in acidic or basic media. Coloration is normally preceded by depoly-... 

Coloured oxidation products, a) Dissolve a few small crystals of diphenylamine in 1 ml. of cone. H2SO4. Add 2 drops of cone. HNO3 to about 10 ml. of water, shake, and add i drop of this diluted HNO3 to the diphenylamine solution an intense purple-blue coloration is produced. Monomethylaniline merely turns a dirty brown when treated in this way. 

Qualitative Analysis. Several quaUtative analyses can be employed. For example, in the oxamide method (59), oxaUc acid is first heated at approximately 200°C with concentrated aqueous ammonia in a sealed tube. When thiobarbituric acid is added and heated to 140°C, a condensed compound of red color forms. The analysis limit is 1.6 pg. In the diphenylamine blue method (59,60), oxaUc acid is heated with diphenylamine to form a blue color, aniline blue. The analysis limit is 5 pg. 

This work supports the suggestion that sulfur dyes are complex thiamines derived generally from diphenylamine units (22). Depending on the conditions of the thionation, two or more thiamine units could be linked by sulfur to produce a typical sulfur blue (17, R = OH or NH2). 

Some other inhibitors from the patent literature include hydroquinone [129], ionoP [130], and quinone [131]. Other inhibitors used to stabilize MMA include butylated hydroxy toluene (BHT), phenothiazine, methylene blue, hydroxy-diphenylamine and di-/jc/<3-napthol [132]. Several good reviews of inhibition and inhibitors have been written [133-136]. The mechanisms of inhibition are subtle and complicated. For example, it has been reported that highly purified benzo-quinone acts as a retarder rather than an inhibitor [137]. It has been proposed... 

To detect glycosides heat the chromatograms to 130—150°C for 15 min. Blue-grey zones are produced (detection limit prunasin 0.3—0.5 pg [18]). Flavonoids are better detected with a modified reagent of the following composition phosphoric acid (85%) — acetic acid — aniline — diphenylamine (20 ml - -100 ml + 5 ml + 5 g). 

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. 

Thus, the dermal nitrate test is a color test for unbumed or partially burned gunpowder, ie, nitrocompds, which form a blue product with the acidic diphenylamine reagent... 

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). 

Several examples of typical triarylmethane dyes have already been mentioned, in particular, pararosaniline (6.161), malachite green (6.162) its o-chloro derivative (6.169), crystal violet (6.164), rosaniline (6.165) and diphenylamine blue (6.173). Cl Basic Green 1 (6.168 R = C2H5), the ethyl analogue of malachite green, is prepared by the aldehyde route and is isolated as the sulphate. The ethyl analogue of crystal violet is Cl Basic Violet 4 (6.167 R = C2H5) and is obtained by the ketone route. 

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... 

Nitramines dissolved in concentrated sulphuric acid give a blue colour with diphenylamine reagent. 

Nitroguanidine and nitrosoguanidine both give a blue colour with diphenylamine in concentrated sulphuric acid and both give the characteristic reactions described below ... 

Diphenylamine behaves not only as a stabilizer, but also as an indicator of the oxidation and decomposition processes which occur in powders. It was noticed long ago that powders containing diphenylamine assume under certain conditions colours ranging from greenish or bluish shades to dark blue or almost black and sometimes to yellow or brown, i.e. ... 

The powder turns dark blue if it contains a large quantity of solvent and if it is exposed to the action of hot air, e.g. on drying at a temperature of 50-60°C. The investigations of Desmaroux [68), Marqueyrol and Muraour [69] and of Mar-queyrol and Loriette [70] showed that this is due to the oxidation of diphenylamine produced by peroxides formed from residual ether and atmospheric oxygen. 

Davis and Ashdown devised methods for detecting these substances in powder. If the alcoholic extract from powder contains diphenylamine it forms a blue colour with ammonium persulphate N-nitrosodiphenylamine gives no coloration with this reagent. The intensity of the colour developed by a mixture of both substances evidently depends upon the concentration of diphenylamine. On the other hand N-nitrosodiphenylamine gives an intense blue coloration to concentrated sulphuric acid. 

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