last updated
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. Make sure that you make progress on your formal report as well in terms of literature research and writing the parts that you completed already in the lab. The draft version of paper is due on 2-1-2008 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 in the draft, the more feedback you will get, which will beneficial for the final version. We will try to return the reports by Monday.
2. The third quiz will be administered on Thursday, January 31, 2008 at 12 pm covering the catalyst and epoxidation. Please make sure that you show up on time. Otherwise you will not be allowed to take the quiz.
3. On Tuesday, January 29, 2008 the class will meet for lecture in YH4335 and YH4336 (Chemdraw training).
4. It is highly advisable to look at the reader prior to attending to lecture. There are a lot of issues to discuss in the individual experiments, but not enough time to discuss every little thing in great detail. It is also recommended to review the techniques that should be familiar to you from 30AL/BL i.e. extraction, recrystallization, TLC, IR/NMR spectroscopy, etc.
1. Referring to the catalyst design, answer the following questions.
a. What is the function of the tert.-butyl groups in the catalyst?
b. Why is the meso form of the ligand not very useful for an asymmetric epoxidation reaction?
c. The Jacobsen ligand forms complexes with many metals. What makes Mn so special compared to Mg and Co?
d. Why are reactions carried out a lower temperatures (T= -78 oC) often times more stereoselective than reaction carried out at room temperature? What is the drawback of these low temperature reactions?
e. Some of the catalyst variations possess methoxy groups on the benzene ring. In which way do these groups improve the catalyst?
2. Referring to the epoxidation reaction carried out in the lab, answer the following questions.
a. The reaction is carried out as a biphasic reaction. Which solvents are used here and which implication does this have for the reaction?
b. The student starts off with a solvent mixture (dichloromethane:hexane=1:1) for TLC. The procedure asks to optimize the mixture? What does this means and how is this accomplished?
c. How are the alkene and the epoxide visualized in the TLC experiment? Outline a brief procedure.
d. Why are 5-10 mol% of the catalyst used? How much would a student use (minimum) if he starts the reaction with 0.50 g of the alkene (M.W.=120 g/mol)?
e. What is the function of the pyridine N-oxide in the reaction?
f. How does the crude product appear after the initial workup?