To rapidly develop extractions of reactions run in water-soluble solvents, e.g. THF and acetonitrile, first try washing reaction aliquots on a test-tube scale. Note any phase separation, the presence of any emulsions that take a significant amount of time to separate, and any losses to the aqueous phase. If problems arise, inorganic salts may be added to the mixture in order to "salt out" the organic product into the organic phase. Effective phase splits may occur if there is less of the organic solvent present, i.e. if the reaction were run more concentrated. A cosolvent such as ethyl acetate or toluene may be added to improve the partition coefficients of the product in the organic and aqueous phases, thus elimination emulsions. As a last resort, replace the reaction solvent with a higher-boiling, more water-immiscible solvent, and reexamine extractions.This is a tip that has a little bit of relevance to the small-scale aqueous extraction that is being annoying and forming an emulsion as well. Remember, as the chemist, you control the vertical and the horizontal.
Wednesday, November 17, 2010
Process Wednesday: aqueous extractions with water-miscible solvents
Another handy tip from Anderson's Practical Process Research and Development: