Separate Racemic (±) Mandelic acid into optically active components by column / adsorption chromatography.

 Separate Racemic (±) Mandelic acid into optically active components by column/adsorption chromatography.

Theory:

Mandelic acid contains one asymmetric carbon atom and exhibits optical rotation. Whenever it is prepared in the laboratory, it is obtained as a racemic mixture (dl or ±). Two optically active isomers can be separated by column chromatography.

Requirements:

• Chromatography tube or column (25 cm x 1.7 cm) 
• Adsorbent alumina (chromatographic grade 100-200 mesh)
• Racemic mandelic acid.
• Benzene.

Procedure:

• Prepare an alumina slurry by mixing about 25 g of alumina in about 40-50 ml. of benzene.
• Pour this slurry into the chromatography tube and prepare a column about 25 cm long. Place the filter paper at the top of the column.
• Take about 5.0 g of Mandelic racemic acid and dissolve it in benzene. 
• Open the faucet of the chromatography column to drain the excess solvent. When the column surface is almost dry add the acid solution from the top of the column.
• Attach the drip funnel to the chromatography tube at the top and fill it with benzene. When the last drop of the mandelic acid solution has entered the column, start adding the benzene from the drip funnel.
• The acid mixture will start to move into the column and the two isomers will separate due to different adsorption by the adsorbent. They will appear as a separate band.
• Separate the two bands by the elution method. 
•  Recover the isomer by evaporation of the benzene solvent.

Precautions:

• There should be no air bubble trapped in the column of alumina.
• Only chromatography-grade alumina should be used for filling the column. 
• For effective separation, the rate of the flow down the column should be about 10 drops per minute.

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