organic_lecture3_10

organic_lecture3_10 - Purification and identification...

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Unformatted text preview: Purification and identification Recrystallization and infrared spectroscopy Recrystallization ¡ Removal of impurities from solid product ¡ Requires a solvent in which there is a solubility difference between impurities and product ¡ Dissolution of organic compounds is usually endothermic ¡ P(s) + heat → P(solvent) ¡ Temperature increase increases solubility if dissolution is endothermic ¡ Warm solvent to dissolve impurities & product ¡ Slowly cool to recrystallize product Recrystallization ¡ Good solvent ¡ Easy dissolution at moderately high temperatures ¡ Low freezing point ¡ Want solvent to freeze below 0°C so that ice bath can be used to recrystallize ¡ Product should crystallize from solvent at or below room temperature, but above 0 o C Recrytallization ¡ Add just enough solvent with heating to dissolve sample ¡ want system just at saturation with respect to product ¡ cool slowly ¡ if too fast ¡ impurities can trapped in crystal lattice ¡ if too slow ¡ impurities can absorb on crystal surfaces. Recrystallization ¡ no crystal formation? ¡ too much solvent ¡ poor solvent choice ¡ insufficient solubility change over temp range ¡ compound too soluble in solvent ¡ supersaturation ¡ options ¡ boil off excess solvent ¡ seed crystallization ¡ choose different solvent © 2005 D.B. King Infrared Spectroscopy...
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This note was uploaded on 11/07/2011 for the course CHEM 356 taught by Professor Rowell during the Summer '10 term at Drexel.

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organic_lecture3_10 - Purification and identification...

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