Shake-flash extraction

It has already been mentioned that the scope of reactions that lend themselves to solution-phase combinatorial chemistry is dependent on the possibility of purifying the products. A number of techniques have been used for this purpose, though their significance often depends on the size of the library and on how easily they can be automated. This applies particularly to most chromatographic methods. One of these that can be easily run in parallel fashion is flash chromatography, and this has therefore also been applied in library synthesis (e.g. [47, 111]) even of mixtures (e.g. [6]). Also simply shaking with sorbents (e.g., alumina/silica gel [115]) may be sufficient to purify the products Extraction procedures have been followed widely in solution-phase combinatorial chemistry, and these and some other techniques will now be reviewed briefly. 

Dissolve 5 g. of hydroxylamine hydrochloride in 10 ml. of water in a small conical flask and add a solution of 3 g. of sodium hydroxide in 10 ml. of water. Cool the solution in cold or ice water, and add 6 g. (7-6 ml.) of acetone slowly. Cool the flash, shake well, and leave overnight, during which time the oxime may crystallise out. If no crystals appear, cork the flash and shake vigorously when the acetoxime usually separates as colourless crystals. Filter the crystals at the pump, dry rapidly between filter paper (yield 2-6 g.) and determine the m.p. (59°). Extract the filtrate with two 20 ml. portions of ether, and remove the solvent a further 0 5 g. of acetoxime (m.p. 60°) is obtained. Recrystal-Use from light petroleum, b.p. 40-60° (CAUTION inflammable) to obtain the pure acetoxime, m.p. 60°. Acetoxime sublimes when left exposed to the air. 

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