Aqueous solutions small-scale extractions

First carry out a small-scale test, placing about 0 5 g. of the mixture in a test-tube, adding about 5 ml. of 10% aqueous NaOH solution, and shaking the mixture well. It will be readily seen whether the neutral substance (which remains undissolved) is solid or liquid. Then repeat the extraction on a largo scale as follows ... 

Biopolymer Extraction. Research interests involving new techniques for separation of biochemicals from fermentation broth and cell culture media have increased as biotechnology has grown. Most separation methods are limited to small-scale appHcations but recendy solvent extraction has been studied as a potential technique for continuous and large-scale production and the use of two-phase aqueous systems has received increasing attention (259). A range of enzymes have favorable partition properties in a system based on a PGE—dextran—salt solution (97) ... 

Detection.—Sulphur in the free state is readily recognisable by its general appearance and characteristics, and especially by its combustion to sulphur dioxide. Both in mixtures and compounds the presence of the element can be demonstrated by heating with charcoal and an alkali carbonate,2 or even better, on a small scale, by heating with an equal bulk of sodium or potassium,3 or with powdered iron 4 in each case some of the sulphur is converted into sulphide, which may be detected by the action of an aqueous extract on mercury or silver, or on sodium nitroprusside the metals are blackened, whilst the nitro-prusside is very sensitive in giving a purple coloration (see p. 62). Alternatively, the solution of the alkali sulphide may be acidified and tests applied for hydrogen sulphide to the vapours evolved on warming. 

Note. (1) For the safe disposal of the aqueous solution see Expt 5.158. A further small quantity of mandelonitrile may be obtained by extracting the aqueous solution with ether, evaporating the ether and adding the residue to the main portion of mandelonitrile. This extraction is hardly worth while except for large-scale preparations. 

In summary, peracetic acid in aqueous solution is an efficient reagent for the epoxidation of a variety of substrates, however, it should be used relatively quickly after its preparation. Sensitive substrates like isoamylene also require a buffer such as sodium hydrogen carbonate to affect high yield of the epoxide. Solvent extraction of an appropriate source of a peracid can lead to organic solutions of the oxidation species. Such methods have been available for many years,43 however, very few are amenable to more than a small scale operation. 

The new tungsten reagents (1-Vl) are also effective for deoxygenation of epoxides to the parent olefin. Reagents V and Vl are the cheapest and most convenient reagents for this purpose however, reagents l-lll serve well for small- and medium-scale reactions. In a typical experiment WCl (0.15 mole) is added to THF (420 ml.) cooled to —62° n-butyllithium (0..30 mole) is added slowly at this temperature. The mixture is allowed to warm slowly to room temperature. The oxide (0.08 mole) is added. A rapid exothermic reduction takes place. After 0.5 hr. the product is poured into an aqueous solution containing sodium tartrate and NaOH. and the olefin extracted with hexane. 

The prospect of separating lithium isotopes on a large scale by the extraction of lithium from aqueous solutions is not very promising. In the system we have studied, reflux could be accomplished by an acid-base mechanism however, because of the small separation factor, an extremely large reflux ratio would be required. This would necessitate a very large plant using enormous quantities of acid and base, and the cost would be excessive. 

Alcohol/water systems have attracted the attention of many scientists and technologists for a number of reasons (i) The low cost of the lower members of the aliphatic alcohols and their miscibility with water make the alcohol/water mixtures useful as industrial solvents for a variety of chemical reactions and for small- and large-scale separation processes. In particular, the aqueous solutions of alcohols are often employed in the extraction and manipulation of labile materials such as proteins. (ii) They have unusual thermodynamic properties that depend in a complex way on composition, pressure, and temperature. ... 

Copper and zinc are the principal metals extracted by electrolysis in aqueous solution the total world production of both approaches 10 ton yr although the electrolytic route accounts for only 10% of the copper and 50% of the zinc produced. Moreover the large electrolytic plants are limited to sites in Africa, Australia and Canada where hydroelectric power is available close to the mines. Cobalt, nickel, chromium, manganese, cadmium, gallium, thallium, indium, silver and gold have also been reported to have been extracted by a hydrometallurgical process but, since these metals are only produced in a low tonnage, the electrolytic processes are on a small scale. 

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