Decolorising carbon

The reaction with permanganate constitutes a valuable and much-used test for unsaturation in an organic compound. The substance is dissolved in cold alcohol, a few drops of sodium carbonate solution are added, and then a drop.of dilute permanganate solution. Rapid disappearance of the red colour indicates the presence of a double bond. The Baeyer test can also be carried out in pure glacial acetic acid, which is stable towards permanganate. Another method of detecting double bonds is by the decolorisation of bromine. As a rule, chloroform is used as solvent. 

A sample of the material, dissolved in a little dilute sodium carbonate solution, should not decolorise a drop of permanganate solution. 

Cao, H. Hardin, I.R. Akin D.E. Optimization of conditions for microbial decolorisation of textile wastewater starch as a carbon source. AATCC Rev., 2001, 7, 37-42. 

Nitrosodisulphonic acid decomposes spontaneously into sulphuric acid, sulphur dioxide and nitric oxide. Its solution is rapidly decolorised on shaking with air or on mixing with hydrogen peroxide, per-mono- or perdi-sulphuric acid, nitric acid, chlorine or potassium chlorate. Most metallic oxides and carbonates decompose the solution, being converted into sulphates.7... 

The bromide may also be prepared (1) by adding arsenic powder to a mixture of carbon disulphide and bromine (2 1 by weight) and agitating the liquid until decolorised 3 on evaporation, crystals of the bromide remain (2) by heating a mixture of arsenious oxide, potassium bromide and acetic acid at 100° C. 4 (3) by heating a mixture of arsenious oxide and sulphur in a current of bromine vapour.5... 

Arsenic subsulphide is a dark brown powder. It is insoluble in carbon disulphide, in aqueous ammonia and in colourless ammonium sulphide. It dissolves, however, in yellow ammonium sulphide, which is at the same time decolorised, and the addition of an excess of hydrochloric acid to the solution precipitates arsenious sulphide. It is decomposed by caustic alkali. When heated, arsenic subsulphide is resolved into realgar and arsenic. 

The same reaction occurs if realgar is added to a solution of iodine in an organic solvent such as carbon disulphide, and the solution is decolorised. 

From Alcohol.—To 32 gms. potassium carbonate dissolved in 80 gms. water 16 gms. 95% alcohol are added, and the solution heated to 70°. 32 gms. powdered iodine are added gradually with stirring. Iodoform gradually separates out, and when the solution has become completely decolorised, is filtered off, washed with water, and dried at ordinary temperature. A further yield is obtained by adding 2—3 gms. potassium bichromate and 16—24 gms. cone, hydrochloric acid, neutralising and adding 32 gms. potassium carbonate, 16 gms. 95% alcohol and 6 gms. iodine, and carrying out as before. 

Total Acidity.—50 or 100 c.c. of the beer, freed from the bulk of the carbon dioxide, are heated for half an hour at 400 to expel the residual gas and are then titrated with N/io-sodium hydroxide, neutral litmus paper or phenolphthalein being used as indicator when phenolphthalein is employed, it is well to add a slight excess of the alkali and then to run in N/10-sulphuric add until the red coloration disappears. When, however, the liquid is too highly coloured to allow accurate observation of the point of neutrality, the procedure is as follows to 20 c.c. of distilled water, previously boiled, are added 10-12 drops of alcoholic phenolphthalein solution and 0 2 c.c. of N/io-sodium hydroxide. The beer is then titrated with the decinormal alkali and, after each addition of the latter, six drops of the liquid are added to one drop of the indicator prepared as above, placed in the depression of a porcelain plate the titration is finished when this indicator is no longer decolorised in this way. The acidity is usually 1 Race Joum. Soc. Chem. Industry, 190S, XXVII, p, 544. 

Indigo carmine is fixed by wool in an acid hath and may then lie removed from the wool by boiling this with dilute sodium carbonate solution. The solution thus obtained gives the following reactions with sulphuric acid, a blue coloration with jxitash it decolorises somewhat, with. stannous chloride, it becomes decolorised m the hot (the colour jcHppcars on addition of ferric chloride) by nitric a id or chlorine water it is ilecohuised (the colour cannot be restored in any way). 

With an equal volume of stannous chloride, the dilute solution of the extract (about 0-5% of dry matter) gives a violet precipitate if the extract is non-fermented or a dark brown precipitate if the extract is fermented. The same solution gives a bluish-violet precipitate with copper acetate, a blackish-blue precipitate with ferric chloride, and a violet precipitate with alum and then sodium carbonate. With chloride of lime it becomes first reddish-brown and then decolorised. 

Qualitative Tests.—The solution of the extract is reddish-yellow with a more or less brown tint by acids it is turned to orange and rendered slightly turbid and by alkalies crimson. Stannous chloride gives a red precipitate with the solution, ferric chloride a reddish-brown precipitate and alum and then sodium carbonate a red precipitate. The solution of the extract is decolorised by chloride of lime and also by sodium sulphite (difference from red sandalwood and the like). 

A mixture of 2-(4-aminophenyl)propionic acid (52.2 g), potassium o-chlorobenzoate (61.5 g), potassium carbonate (43.6 g) and copper powder (0.3 g) in amyl alcohol (620 ml) is heating under reflux for 16 h. The major proportion of the solvent is then removed by steam distillation. The residual aqueous solution is treated with decolorising charcoal (20.0 g) and acidified with 4 N sulfuric acid (220 ml). The cream product which crystallises is dissolved in diethyl ether (500 ml). 

Another satisfactory process for the determination of total hardness, based on a somewhat similar principle, is due to Blacher.4 The water is first titrated with decmormal hydrochloric acid until it is neutral to methyl orange, as in the method described above for temporary hardness. After the removal of the carbon dioxide by a current of air, the methyl orange is bleached by the addition of a drop of bromine water a little phenolphthalein and a few drops of alcoholic potassium hydroxide are added, the liquid is just decolorised with dccinormal hydrochloric acid and is then titrated with an alcoholic decmormal solution of potassium palmitate until a decided red colour is produced. The quantity of the potassium palmitate solution required is proportional to the total hardness. 

This body is obtained by action of phenol on phthalic anhydride in presence of strong sulphuric acid. The free phthalein forms colourless crystals, melting at about 350° it dissolves in alkalies with a red colour, and is precipitated by acids as a white precipitate. The alkaline solution is decolorised by excess of alkali. On melting with caustic potash, it yields benzoic acid and dioxy-benzophenone. On account of the change in colour occasioned by free alkalies (not carbonate or ammonia), phcnolphthalein is useful as an indicator in titration. 

Dimethylcyanine [4].—The iodide C21H19N2I is formed from the methyl iodides of quinoline and lepidine. It forms lustrous green needles, M.P. 291°. Its blue solution is decolorised by carbonic acid. The ethyl iodides of the above bases form the corresponding cyanine iodide C23H23N2I. 

Pyridine (26 g) is wanned with glacial acetic acid (100 ml) and perhydrol (50 ml) on a boiling water-bath for 24 h, then the acetic acid is removed in a vacuum. The residual oxide is dissolved with ice-cooling in concentrated sulfuric acid (70 ml), treated with a mixture of concentrated nitric acid id 1.52 110 ml) and concentrated sulfuric acid (70 ml), and heated in an oil-bath at 130° (internal temperature) for 2.5 h. Next, nitric oxide is led in while the temperature is raised slowly to 200°. When the evolution of nitrous fumes ceases, the mixture is allowed to cool in a stream of nitric oxide and then poured on ice. The pH is then adjusted to 6 with sodium carbonate, the precipitate is filtered off and dissolved in chloroform, and the filtrate is made weakly alkaline and shaken three times with chloroform. The united chloroform solutions are extracted with water, decolorised with animal charcoal, dried over sodium sulfate, and evaporated in a vacuum. When dissolved in light petroleum, brought to the boil, and allowed to crystallize with ice-cooling, the residue forms white flakes, m.p. 50° (26.4 g, 71%). 

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