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Problems Set #6
ATTN: answers to the below questions are due at the start of your lab period of Meeting 6; these answers should be part of your pre-lab write-up.
Announcements:
1. The next quiz will be on February 2, 2006 at 12 pm. The material covered will mainly include the ligand and catalyst synthesis, epoxidation and the theoretical aspects.
2. The draft version of paper is due on 2-3-2006 at 5 pm. The draft version is worth 15 points, the final paper 45 points. For more information what the draft is supposed to contain see here. Late submission will receive less credit. The more of your work you submit here, the more feedback you will get, which will beneficial for the final version. We will try to return the reports by Monday.
1. Referring to the epoxidation reaction carried out in the lab,
a. what is used as oxygen source in this reaction?
b. why is a two-phase system used in this reaction?
c. why is hexane added during the work-up?
d. why is TLC used in this reaction?
e. Why is "ceric staining" used to visualize the epoxide in the TLC experiment? How does this work?
2. A student plans to use 1.5 g of a-methylstyrene for his epoxidation. His procedure requires the use of 5 mole% of the Jacobsen catalyst and 1.1 equivalents of bleach.
a. How many grams of the catalyst are needed in this reaction?
b. What is the volume of bleach required in this experiment?
c. Your fellow student decides to use pentane as a solvent here. What would you tell him/her?
3. Why is it virtually impossible to achieve an e.e.-value of 100% for the epoxidation carried out in the lab?
4. Referring to the design of the catalyst, answer the following questions.
a. Which function do the tert.-butyl groups have in the catalyst?
b. Why are only the (R,R) and the (S,S)-form of the catalyst used in asymmetric synthesis?
c, Why a metal complex used as a catalyst and not "Mn3+" itself?