1) During the work-up procedure of our second reaction (“Hydrogenation of a Chalcone”), the following steps...

1) During the work-up procedure of our second reaction (“Hydrogenation of a Chalcone”), the following steps are performed:

a) Add 15 mL of brine and 10 mL of ethyl acetate to the mixture. Shake vigorously, then separate the ethyl acetate layer from the aqueous phase. Store the ethyl acetate layer in a dry, clean Erlenmeyer flask.

b) Extract the aqueous phase again with an additional 5 mL of ethyl acetate.

c) Combine the two ethyl acetate solutions and wash this ethyl acetate layer with 5

mL of brine. Drain the aqueous phase and pour the ethyl acetate solution into a

clean 25-mL Erlenmeyer flask.

d) Dry the organic phase with anhydrous magnesium sulfate for 5 min.”

Why are we performing each of the four steps mentioned above? (What is the purpose?) Please explain.

Expert Solution

The product of your experiment is an organic compound(aldol),but the medium used for the reaction is aqueous (basic),with NaOH and aq ethanol as solvents.

To separate the organic chalcone product from aqueous medium, brine or salt solution is added,which precipitates the organic compond from aq medium.This method is called salting out.In the presence of an electrolyte the solubility of non-electrolyte decreases in aqueous medium and thus separates.

Ethyl acetate is polar aprotic solvent which dissolves the aldol(chalcone product) very well.So it is used to extract the separated product from the aq medium by solvent extraction procedure.

Solvent extraction is repeated by using several small volumes of organic solvent (ethyl acetate) to extract the maximum product from aq layer.

Later on traces of water is removed from organic solvent ,with the product dissolved in it,using MgSO4. which absorbs water in its anhydrous form to get converted into hydrated MgSO4.7H2O

This ensures your solvent is completely dried of moisture.

Later on the organic solvent can be evaporated to give the product..

http://www.wisegeek.org/what-is-solvent-extraction.htm

queen_honey_blossom answered 18 hours ago

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