Dry-column flash chromatography

Dry-column flash chromatography. This technique has been developed from flash chromatography by L. M. Harwood.64 The principal feature is that suction is applied to the column packing, and eluting solvents are added in predetermined volumes with the column being allowed to run dry before the next fraction is added. Furthermore the apparatus is both simple and of easy operation. 

The crude product from step 10 above is purified by dry column flash chromatography. cf gnj then by recrystallization from a mixed solvent of petroleum ether and ethyl acetate (1 1 ) to yield colourless crystals (m.p. SY-eOT). 

An improved method, utilizing a capillary Pasteur pipet for introducing the sample onto the chromatographic column approximately doubles the effectiveness (theoretical plates) of the column. Dry-column flash chromatography has been adapted for use in the instructional laboratory. The "column" consists of a dry bed of silica gel in a sintered glass funnel placed in a standard vacuum filtration flask the solvent is eluted by suction. Small (16 X 150-mm) test tubes inserted into the flask below the stem of the funnel are used to collect the fractions. This technique has been used successfully to separate mixtures ranging from 150 to 1000 mg. 

Mother liquors from the production of bromocriptine 2 were dried by evaporation under vacuum. The dry residue (82.2 g) was applied on chromatographic column (I.D. = 3 cm, lenght = 20 cm) packed with silicagel 60, granulation 0.063 - 0.040 mm and eluted by flash - chromatography with pure dichloromethane. Two separate fractions were obtained and crystallized from dichloromethane (- 15°C). 

With telluronium salt (c) (generalprocedure) A solution of n-BuLi (1.5 mmol) in hexane is added to a solution of the telluronium salt (0.475 g, 1.5 mmol) in dry THF at -70°C under N2. After 1 h a solution of the carbonyl compound (1.0 mmol) in THF (2 mL) is added. After the reaction is complete (monitored by TLC), AcOEt is added. The resulting mixture is filtered through a short Si02 column. The solvent is evaporated under vacuum, and flash chromatography gives pure cyanomethylcarbinol. 

The submitters purified the product by flash chromatography as follows. Tetrahydrofuran is removed on a rotary evaporator. Silica gel (20 g) and 80 mL of acetonitrile (Note 2) are added to the flask. The resulting slurry is concentrated with a rotary evaporator to a dry solid. The material is scraped from the flask and loaded onto a flash chromatography column (50 mm... 

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