Evaporation of acids

The possibility of preconcentration of selenium in form of SeO by evaporation of low alkali water solution (for 20-1000 J.g/L) has been investigated. Considerable losses of selenium have been observed during evaporation of acidic and neutral solutions owing to volatility of selenium compounds. During evaporation of low alkali solutions at ph 9-10 there are no losses of selenium. Relative error of selenium determination is 1-2% for 1000 P-g/L solution and 3-5% for 20-100 p.g/L. Concentration factor is 10. 

Perform all work with substances that are poisonous or have an unpleasant odour, and also the evaporation of acids and acidic solutions only in a fume cupboard work far from a flame with flammable substances. 

A cheaper but less controllable device for steady evaporation of acids to dryness is the air bath shown diagramatically in Fig. 3. It consists of an aluminium sheet box with the vertical sides insulated with Sindanyo sheet. The bottom is open and rests on an ordinary hot plate. The top is drilled to hold test-tubes suspended by the rims. The temperature can be controlled by judicious use of the hot plate control for the gentle evaporation of... 

Peptides containing the Asp-Pro (DP) sequences are very sensitive to acidic conditions (41,42). To prevent cleavage of the Asp-Pro bond, careful handling is necessary even in dilute acids. Evaporation of acidic solvents in elevated temperature (over 20°C) or storage in acidic solution may lead to decomposition of Asp-Pro-containing peptides. 

The separation of isotopes by ion exchange requires repeated evaporation of acids. In order to protect fume hoods and the environment, this is preferably done by heating the beakers with an infrared lamp under a vented glass cover (Fig. 13-2). 

Hydrolysis of Potassium Ethyl Sulphate. Dissolve about i g. of the crystals in about 4 ml. of cold distilled water, and divide the solution into two portions, a) To one portion, add barium chloride solution. If pure potassium ethyl sulphate were used, no precipitate should now form, as barium ethyl sulphate is soluble in water. Actually however, almost all samples of potassium ethyl sulphate contain traces of potassium hydrogen sulphate formed by slight hydrolysis of the ethyl compound during the evaporation of its solution, and barium chloride almost invariably gives a faint precipitate of barium sulphate. b) To the second portion, add 2-3 drops of concentrated hydrochloric acid, and boil the mixture gently for about one minute. Cool, add distilled water if necessary until the solution has its former volume, and then add barium chloride as before. A markedly heavier precipitate of barium sulphate separates. The hydrolysis of the potassium ethyl sulphate is hastened considerably by the presence of the free acid Caustic alkalis have a similar, but not quite so rapid an effect. 

Ethyl bromide soon distils over, and collects as heavy oily drops under the water in the receiving flask, evaporation of the very volatile distillate being thus prevented. If the mixture in the flask A froths badly, moderate the heating of the sand-bath. When no more oily drops of ethyl bromide come over, pour the contents of the receiving flask into a separating-funnel, and carefully run oflF the heavy lower layer of ethyl bromide. Discard the upper aqueous layer, and return the ethyl bromide to the funnel. Add an equal volume of 10% sodium carbonate solution, cork the funnel securely and shake cautiously. Owing to the presence of hydrobromic and sulphurous acids in the crude ethyl bromide, a brisk evolution of carbon dioxide occurs therefore release the... 

Place a mixture of 25 g. of a-naphthylamine (Section IV,37) and 125 g. (69 -5 ml.) of concentrated sulphuric acid in a 250 ml. conical or round-bottomed flask, and heat in an oil bath for 4-5 hours or until a test sample, when made alkaline with sodium hydroxide solution and extracted with ether, yields no naphthylamine upon evaporation of the ether. Pour the warm reaction mixture cautiously and with stirring into 300 ml. of cold... 

Add 50 g. of the crude acetothiomorpholide to 400 ml. of 10 per cent, alcoholic sodium hydroxide solution and reflux the mixture for 10 hours. Distil off most of the alcohol, add 100 ml. of water to the residue, and strongly acidify the alkahne solution with hydrochloric acid. Cool, extract thrice with ether, dry the combined ether extracts, evaporate the solvent, and recrystallise the residue from water or dilute alcohol. The yield of p-methoxyphenylacetic acid, m.p. 85-86°, is 26 g. A further quantity of acid may be obtained by extracting the mother hquors with ether. 

Step 2. Extraction of the basic components. Extract the ethereal solution (Ej) with 15 ml. portions of 5 per cent, hydrochloric acid until all the basic components have been removed two or three portions of acid are usually sufficient. Preserve the residual ethereal solution (E2) for the separation of the neutral components. Wa.sh the combined acid extracts with 15-20 ml. of ether discard the ether extract as in Step 1. Make the acid extract alkaline with 10-20 per cent, sodium hydroxide solution if any basic component separates, extract it with ether, evaporate the ether, and characterise the residue. If a water-soluble base is also present, it may be recognised by its characteristic ammoniacal odour it may be isolated from the solution remaining after the separation of the insoluble base by ether extraction by distilling the aqueous solution as long as the distillate is alkahne to htmus. Identify the base with the aid of phenyl iso-thiocyanate (compare Section 111,123) or by other means. 

In a typical procedure, a solution of 0.175 mmol of L- -amino acid and 0.175 mmol of NaOH in 1 ml of water was added to a solution of 0.100 mmol of Cu(N03)2in 100 ml of water in a 100 ml flask. Tire pH was adjusted to 6.0-6.5. The catalyst solution was cooled to 0 C and a solution of 1.0 mmol of 3.8c in a minimal amount of ethanol was added, together with 2.4 mmol of 3.9. The flask was sealed carefully. After 48 hours of stirring at 0 C the reaction mixture was extracted with ether, affording 3.10c in quantitative yield After evaporation of the ether from the water layer (rotary evaporator) the catalyst solution can be reused without a significant decrease in enantioselectivity. 

To a mixture of 25 ml of water and 3 ml of 95% sulfuric acid were added 40 ml of DMSO. The mixture was cooled to 10°C and 0.20 mol of l-ethoxy-l,4-hexadiyne (see Chapter III, Exp. 51) was added with vigorous stirring in 15 min. During this addition, which was exothermic, the temperature of the mixture was kept between 20 and 25 0. After the addition stirring was continued for 30 min at 3S C, then 150 ml of water were added and six extractions with diethyl ether were carried out. The combined extracts were washed with water and dried over magnesium sulfate. Evaporation of the solvent in a water-pump vacuum, followed by distillation through a 25-cm... 

Liquid Effluents. Recycling of acid, soda, and zinc have long been necessary economically, and the acid—soda reaction product, sodium sulfate, is extracted and sold into other sectors of the chemical industry. Acid recovery usually involves the degassing, filtering, and evaporative concentration of the spent acid leaving the spinning machines. Excess sodium sulfate is removed by crystallization and then dehydrated before sale. Traces of zinc that escape recovery are removable from the main Hquid effluent stream to the extent that practically all the zinc can now be retained in the process. 

Cyanides. Salts of the complex ion, [Au(CN)2] , can be formed directiy from gold, ie, gold dissolves ia dilute solutions of potassium cyanide ia the presence of air. Additionally, a gold anode dissolves ia a solution of potassium cyanide. The potassium salt can be isolated by evaporation of the solution and purified by recrystallization from water (177). Boiling of the complex cyanide ia hydrochloric acid results ia formation of AuCN [506-65-01]. Halogens add oxidatively to [Au(CN)2] to yield salts of [Au(CN)2X2] which are converted to the tetracyanoaurates usiag excess cyanide (178). These last can also be prepared directiy from the tetrahaloaurates. 

The parent acid of the hexakiscyanoferrate(3—) salts is ferricyanic acid [17126464] (trihydrogen hexakiscyanoferrate). Red-brown needles are obtained by evaporation of solutions prepared by adding sulfuric acid to tribarium bis(hexakiscyanoferrate). The acid is used to prevent metal surface corrosion. 

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