Question

Why are we performing each of the following four steps during the work-up of the second synthesis (“Hydrogenation of a Chalcone”)? (What is the purpose of each step?) Please explain.

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.

Answer 1

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.

this is essentially an extraction, we are sending organic nonpolar material to the ethyl acetate mix, whereas the inorganic material + polar will go to the brine

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

We do this to assure % recovery of organic material

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.

we do this to get rid of polar/inorganic material in the ethyl acetate solutions

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

we dry in order to avoid H2O and other moisture material in the organic materials.