Sulphur Precipitated

If a substantial amount of sulphur precipitates during the reaction, filter the solution in an inert argon or nitrogen atmosphere through a glass filter No. 2 (see Fig. 645). The receiver for the filtrate must be clean and dry. Keep the inert atmosphere and add 250-300 ml of absolute diethyl ether to the filtrate, introducing it in 20-25-ml portions every 10 minutes. 

Sodium thiosulphate solution yellow colour of solution discharged and sulphur precipitated, owing to reduction. 

Sulphur by the Liebig Method.—By the Liebig method the compound is fused, with sodium or potassium hydroxide, in a silver crucible. When fused, a little potassium nitrate is added as an oxidizing agent. The sulphur of the organic compound is thus converted into sodium or potassium sulphate. The fused mass is dissolved in water, acidified with nitric acid, and the sulphur precipitated as barium sulphate by the addition of barium nitrate. 

With this process, the system is freed from the solid sulphur precipitate. 

However, they do establish broad patterns of exports and imports of sulphur in Europe, although in sensitive areas such as southern Norway, the source of a large proportion of the sulphur precipitation cannot be accounted for. 

Hence, it is usual to employ mildly acidic conditions to destroy sulphides in solution in order to minimise the amount of H2O2 required. In the gas phase, hydrogen sulphide can be removed by scrubbing the gas stream with a hydrogen peroxide solution. Here, alkaline conditions are more effective owing to better absorption of H2S and avoidance of sulphur precipitation in the scrubber. 

The electrodeposition process is comparatively easy to control. Virtually any size and shape of substrate can be plated once it is conductive. This method can therefore be used to deposit semiconductors on patterned substrates. By adjusting the pH of the deposition bath, undesired effects such as sulphur precipitation can be controlled in certain electrolytes such as ones containing elements like sulphur and selenium. By simply varying the stirring rate, the... 

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

The phthalocyanines must be suitably dis-p>ersed to be used as pigments or they can be sulphonated to water-soluble forms for dyeing and for precipitation as lakes. The dispersion is carried out by solution in sulphuric acid, followed by precipitation in water. 

Ag" (precipitate of AgSCN) and (red colouration). Photographic sulphur sensitizers. With oxidizing agents (MnOj, Br ) give thiocyanogen, (SCN)2, which polymerizes above O C. 

Sulphuric acid is added to the electrolyte and the hydroxylamine is formed as hydroxylammonium sulphate, (NH30H)2S04 [cf, (NHJjSOj. Addition of barium chloride then precipitates barium sulphate and hydroxylammonium chloride, (NH30H)C1, is obtained. 

Hence the orange colour of a dichromate is converted to the green colour of the hydrated chromium(III) ion, Cr ", and sulphur is precipitated when hydrogen sulphide is passed through an acid solution.)... 

In all the above methods, the sulphur dioxide obtained is impure. Dust is removed by first allowing the gases to expand, when some dust settles, then by passage through electrostatic precipitators and finally by washing with water. Water is removed by concentrated sulphuric acid which is kept in use until its concentration falls to 94%. 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

Hydrolysis of Aspirin. Gently boil a mixture of i g. of aspirin and 15 ml. of 10% sodium hydroxide solution in a 50 ml. conical flask under reflux for 20 minutes. Then cool the solution thoroughly and add dilute sulphuric acid until the precipitation of the... 

Hydrolysis to p-Nitroaniline. For this purpose use 70 sulphuric acid, the usual reagent employed for the hydrolysis of anilides (p. 108). Add 5 g. of the recrystallised />-nitro-acetanilide to 30 ml. of 70%sulphuric acid, and boil the mixture gently under a reflux water-condenser for 20 minutes. Then pour the clear hot solution into about 150 ml. of cold water, and finally add an excess of sodium hydroxide solution until precipitation of the yellow p-nitroaniline is complete. Coo the mixture in ice-water if necessary, and then filter at the pump, wash well... 

Hydrolysis of />-Tolunitrile. As in the case of benzonitrile, alkaline h> drolysis is preferable to hydrolysis by 70% sulphuric acid. Boil a mixture of 5 g. of p-tolunitrile, 75 ml. of 10% aqueous sodium hydroxide solution and 15 ml. of ethanol under a reflux water-condenser. The ethanol is added partly to increase the speed of the hydrolysis, but in particular to prevent the nitrile (which volatilises in the steam) from actually crystallising in the condenser. The solution becomes clear after about i hour s heating, but the boiling should be continued for a total period of 1-5 hours to ensure complete hydrolysis. Then precipitate and isolate the p-toluic acid, CH3CgH4COOH, in precisely the same way as the benzoic acid in the above hydrolysis of benzonitrile. Yield 5 5 g. (almost theoretical). The p-toluic acid has m.p. 178°, and may be recrystallised from a mixture of equal volumes of water and rectified spirit. 

If the original compound contains sulphur, a black precipitate may be produced at this stage. 

Principle. A known weight of the substance is heated with fuming nftric acid in a sealed tube, the organic material being oxidised to carbon dioxide and water, and the sulphur to sulphuric acid. The latter is subsequently washed out of the tube, precipitated as barium sulphate, and estimated as such... 

If a solution of 18 g. of barium sulphate in one litre of concentrated sulphuric acid is employed, a precipitate of barium sulphate will form when sufficient water has been absorbed to render it un6t for drying recharging will then, of course, be necessary. 

Cuprous bromide. The solid salt may be prepared by dissolving 150 g. of copper sulphate crystals and 87 5 g. of sodium bromide dihydrate in 500 ml. of warm water, and then adding 38 g. of powdered sodium sulphite over a period of 5-10 minutes to the stirred solution. If the blue colour is not completely discharged, a little more sodium sulphite should be added. The mixture is then cooled, the precipitate is collected in a Buchner funnel, washed twice with water containing a little dissolved sulphurous acid, pressed with a glass stopper to remove most of the liquid, and then dried in an evaporating dish or in an air oven at 100 120°. The yield is about 80 g. 

Decompose the addition product by the careful addition of a solution of 32 g. (17-5 ml.) of concentrated sulphuric acid in 175 ml. of water during about 30 minutes. Cool the flask in ice and shake frequently during the addition of the cold, dilute acid the precipitate will decompose... 

Equip a 1-litre three-necked flask with a powerful mechanical stirrer, a separatory funnel with stem extending to the bottom of the flask, and a thermometer. Cool the flask in a mixture of ice and salt. Place a solution of 95 g. of A.R. sodium nitrite in 375 ml. of water in the flask and stir. When the temperature has fallen to 0° (or slightly below) introduce slowly from the separatory funnel a mixture of 25 ml. of water, 62 5 g. (34 ml.) of concentrated sulphuric acid and 110 g. (135 ml.) of n-amyl alcohol, which has previously been cooled to 0°. The rate of addition must be controlled so that the temperature is maintained at 1° the addition takes 45-60 minutes. AUow the mixture to stand for 1 5 hours and then filter from the precipitated sodium sulphate (1). Separate the upper yellow n-amyl nitrite layer, wash it with a solution containing 1 g. of sodium bicarbonate and 12 5 g. of sodium chloride in 50 ml. of water, and dry it with 5-7 g. of anhydrous magnesium sulphate. The resulting crude n-amyl nitrite (107 g.) is satisfactory for many purposes (2). Upon distillation, it passes over largely at 104° with negligible decomposition. The b.p. under reduced pressure is 29°/40 mm. 

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