Hydrochloric acid, impurities preparation

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

For many years a major route to the production of vinyl chloride was the addition of hydrochloric acid to acetylene (Figure 12.5). The acetylene is usually prepared by addition of water to calcium carbide, which itself is prepared by heating together coke and lime. To remove impurities such as water, arsine and phosphine the acetylene may be compressed to 15 Ibf/in (approx. 100 kPa), passed through a scrubbing tower and chilled to -10°C to remove some of the water present and then scrubbed with concentrated sulphuric acid. 

The light-absorbing impurities of oxytetracycline hydrochloride and oxytetracycline dihydrate [2,4,6] are detected using a UV-spectrophotometric method. In all the compendia, the absorbance of a solution of 2.0 mg/mL in a mixture of 1 volume of hydrochloric acid solution (0.1 mol/L) and 99 volumes of methanol at 430 nm not greater than 0.50 is required the absorbance of a solution of 10 mg/mL in the same solvent at 490 nm is not greater than 0.20. The measurements are carried out within 1 h of the preparation of the solutions. 

Whilst preparing hexammino-triol-dicobaltic sulphate from chloro-diaquo-triammino-cobaltic sulphate, Werner 1 obtained a reddish-brown mother-liquor, and on cooling this he obtained from it a green precipitate on the addition of concentrated hydrochloric acid. On dissolving this in water containing a little acetic acid and adding sodium sulphate, the impure hexammino-hexol-tricobaltic sulphate separates. This is collected, treated with ammonium chloride, and greenish-brown crystals of the pure chloride obtained. 

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