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 activity. Whenever prepared in the laboratory, it is obtained as a racemic (d) or ±) mixture. The two optically active isomers can be separated by column chromatography.

Requirements:

• Chromatography column 
• Adsorbent alumina (chromatographic grade 100-200 mesh)
• Racemic mandelic acid.
• Benzene. 

Procedure:

• Prepare a slurry of alumina by mixing about 25 g of alumina in about 40-50 ml. of benzene.
• Pour this slurry in the chromatography tube and prepare a column about 25 cm long. Place the filter paper disc at the top of the column.
• Take about 5.0 g of racemic Mandelic acid and dissolve 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 separate bands.
• Separate the two bands by elution method. 
• Recover the isomers by evaporation of the solvent benzene.

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