last updated Monday, October 16, 2006

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 October 23, 2006 at 12 pm. The material covered will include the catalyst synthesis, the epoxidation and the theoretical aspects.

2. The draft version of paper is due on 10-27-2006 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, answer the following questions.

a. How is the reaction time optimized in this reaction?

b. Na₂HPO₄ is added to the reaction mixture. Rationalize this step.

c. TLC is used in this reaction. Which purpose does it serve?

d. How is the alkene and the epoxide visualized in the TLC experiment? Outline a brief procedure.

e. Why is it important to remove the catalyst after the reaction? How is this accomplished?

f. Flash chromatography is used to purify the crude product. Before the sample is applied to the column, a 1% NEt₃ solution is applied to the column. Rationalize this step.

2. Referring to the design of the catalyst, answer the following questions.

a. One of the problems in the design of the catalyst was to find the correct "blocking groups" on the ring system. What would you expect to happen if the t-butyl groups would be replaced by methyl and t-CPh₃ groups? Explain briefly.

b. If a cis-alkene was used as reactant, a mixture of cis and trans epoxide would be obtained. Rationalize this observation.