Meeting 8/9 Problem Set

Announcements:

1. The Grignard project will take about 1.5 lab periods. This means that most of the students will finish up the project during meeting 9. In addition, there will be also an NMR lab during this meeting which is also mandatory.

2. If you receive a three-necked flask instead of a round bottom flask, you do not need to use a Claisen adapter in your setup anymore. If you break the round bottom or three-necked flask, you will receive an automatic zero for the lab because it shows carelessness. In addition, you will have to pay for the damage!

3. The assigned reading "Moulay, S., Chem. Educator 2003, 8, 393" is on reserve online. We do not have a subscription for this journal anymore.

ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up

1. Referring to the Grignard reaction, answer the following questions. Show pertinent chemical equations where appropriate.

a. Water should be excluded from the reaction as much as possible. Why is this very important here? How is this accomplished?

b. Why is the reaction mixture cooled during the initial stage of the reaction?

c. After the reaction mixture is refluxed, 10% sulfuric acid is added. Which purpose does this step serve and which precautions have to be taken here?

d. After the extraction with diethyl ether, the combined organic layers are extracted with sodium bicarbonate solution. Rationalize this step.

e. After drying organic layer, the solvent has to be removed. How is this done in the lab? How does the product look at this point?

f. High boiling petroleum ether is used for recrystallization. Rationalize this choice.

g. Why is it important that the solution is not placed in an ice-bath during the recrystallization step?

h. Assuming that you want to assess the purity of the crude product, and you are given the following solvents in the lab (heptane, methanol, acetone and dichloromethane), which solvent would be most suitable for the TLC? Sketch a TLC plate for the crude product using this solvent (Hint: Which product are most likely found in the crude?).