Column chromatography decolorization

In a 50-mL, two-necked flask, 100 mg (0.3 mmol) of octacarbonyl dicobalt, Co2(CO)8, is dissolved in 10 mL of toluene. Then 400 mg (0.7 mmol) tppts is dissolved in 10 mL water and added to the solution. The reaction mixture is stirred for 3 h at room temperature. During the reaction the organic phase is decolorized, whereas the water phase turns brown. The mixture is transferred to a separation funnel while maintaining exclusion of oxygen. After the phases have separated, the organic phase is washed twice, in each case with 5 mL of water, and the combined aqueous phases are washed twice, in each case with 5 mL of toluene. The organic phases are discarded. The water phases are collected and the solvent is removed in a vacuum. The crude product is purified by column chromatography on Sephadex G-25. Yield 370 mg (81%) brown powder. 

The aqueous solution containing 3 -deoxykanamycin B in free base form by addition of concentrated sulfuric acid give the 3 -deoxykanamycin B sulfate (tobramycin sulfate). The solution of this compound is decolorized by stirring of Darco G-60, filtered and purified by column chromatography. 

The pentenyl mannoside 76 (3.90 g, 9.11 mmol) and Et NBr (1.47 g, 4.55 mmol) were dissolved in CHjClj (20 mL). The mixture was cooled to 0°C. Bromine (1.46 g, 9.11 mmol) was added dropwise while allowing the solution to decolorize between addition of successive drops. When the brown color persisted, the reaction was quenched with 10% NajSjOj. The organic phase was dried (Na SO ) and the solvent was removed by rotary evaporation. The residue was purified by column chromatography on silica gel (15% 30%, EtOAc-... 

Unused chromatography, recrystallization, and thin-layer chromatography solvents should be placed in the organic solvents container. The alumina from the column should be placed in the hood to allow the petroleum ether and ether to evaporate from it. Once free of organic solvents, it can be placed in the nonhazardous solid waste container. The decolorizing charcoal, once free of solvent, can also be placed in the nonhazardous solid waste container. 

Two other methods have been approved by AOAC for determination of sulfites in food. One is a quantitative assay based on malachite green decolorization using flow injection analysis. Sulfite is released from a sample slurry with alkali, then the test stream is acidified to produce sulfur dioxide gas which diffuses across a Teflon membrane into a flowing stream of malachite green, and the extent of decolorization is measured at 615 nm. The other method is based on ion exclusion chromatography with sulfur dioxide being released by alkali extraction, and the diluted filtrate is injected onto an anion exclusion column linked to an electrochemical detector. 

Microscale decolorization of a solution on a chromatography column requires that a column be prepared in a Pasteur pipette, using either alumina or silica gel as the adsorbent (Section 19.6). The sample to be decolorized is diluted to the point where crystallization within the column will not take place, and it is then passed through the column in the usual manner. The desired compound is collected as it exits the column, and the excess solvent is removed by evaporation (Technique 7, Section 7.10). 

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