Lab 4 - Experiment #4. Flash Liquid Column Chromatography...

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CHEM 237 Lab Fall 2009 Objective The purpose of this experiment is to separate a mixture of two compounds (benzyl alcohol and benzylbromide) using flash liquid column chromatography. Polarity of the compounds and intermolecular attractive forces will be studied. Purity of each compound separated will be checked by TLC and HPLC. R 5 10 f value (TLC) and elution time (HPLC) of each compound will be measured. Reagents Benzyl alcohol Benzyl bromide Ethyl acetate (eluent for LC) 15 Hexanes (eluent for LC) Acetonitrile (eluent for HPLC) Silica gel (stationary phase or absorbent for LC) OH Benzyl bromide Benzyl alcohol Br 20 Apparatus Erlenmeyer flasks Vials TLC plate (SiO 2 ) Glass pipette and micropipette 25 Graduate Cylinder (10 mL and 100 mL) Theory The principle of flash liquid column chromatography is based on attraction between compounds and the stationary (absorbent) and mobile (eluent) phases of chromatography. Polar compound is attracted to the surface of the stationary phase such as polar silica gel (SiO 30 35 40 45 50 55 60 65 70 75 80 85 90 95 2 ) or alumina (Al 2 O 3 ) containing oxygen via H- bonding, dipole-dipole force, London disperson force. Each compound of the mixture loaded on column chromatography travels down at a different rate depending on polarity of the compound and strength of the attractive force between the compound and the stationary or mobile phase. More polar molecule of the mixture will be more tightly bound to the surface of the absorbent and move slower through the column than less polar one. Compound can also interact with a mobile phase by the intermolecular attraction forces. Polar eluent (ex. methanol or ethyl acetate) make a polar compound travel down faster as it pass through the column and dissolve the compound, while non-polar solvent (ex. hexanes) will little affect elution of a polar compound.
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This note was uploaded on 03/03/2010 for the course CHEM 237 taught by Professor Chong during the Fall '10 term at Illinois Tech.

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Lab 4 - Experiment #4. Flash Liquid Column Chromatography...

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