last updated Tuesday, April 06, 2010

1. General

Make sure that you keep writing on your formal report. See your teaching assistant or instructor if you have questions about the format.

Review the following topics: 1H-NMR and 13C-NMR spectroscopy, GC/MS

2. Experiment (Jacobsen Catalyst)

If you do not have 0.40 g of the Jacobsen ligand, you have to downscale the other reagents accordingly. If you do not have sufficient ligand to move on (0.25 g), you will have to repeat the ligand synthesis.

It is highly advisable to crush up the Mn(OAc)2 a little bit in order to increase the rate of the reaction. (How does this work?)

The round bottom flask used should not be more than half full. Why?

Make sure that the air stream and the temperature of the hotplate is not too high during the reaction . If the solvent level lowers too much, the reaction will not take place anymore. Keep the solvent level around 20 mL in the flask (by adding more solvent if necessary). The gas inlet tube has to be immersed into the suspension in order to increase the uptake of oxygen.

Since the glass tube that you will check out from lab support has a smaller diameter than the tubing used at the air line, the diameter has to be increased by wrapping a small amount of parafilm around it at the top. Do not use a Pasteur Pipette since it will clog up easily if the volume of the solvent goes down!

The reaction has to be monitored by TLC in order to determine when it is completed. How do you know that?

The removal of the dichloromethane should be done at low heat using an air stream. However, the evaporation should be done slowly. Why?

How does the student know that the evaporation step is completed?

3. Things to think about

a. Why do you have to reflux the ligand initially with 15 mL of ethanol?

b. Which solvent mixture is used in this experiment for TLC according to the literature?

c. Why is a mixture of dichloromethane and heptane used in the procedure and not dichloromethane and pentane?

d. Why do we not determine the optical purity of the catalyst?

e. Why are there no NMR spectra online for the catalyst?