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 0C 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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organic_lecture3_10 - Purification and identification...

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