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. The Grignard solution is placed in an ice-bath prior to the addition of the benzoin solution. Rationalize this step.

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. Often times the crude product is obtained as an oil. Rationalize this observation. How should the student proceed here?

e. A student uses dichloromethane as solvent for recrystallization. What would he observe?

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

2. Referring to the TLC part of the experiment, answer the following questions.

a. Assume that the following solvents are provided in the lab: hexane, ethanol and ethyl acetate. Which single solvent would be most suitable for the TLC in order to accomplish a good separation between the product and the reactant?

b. Which compounds should be spotted on the TLC plate in the lab?

c. Which solvent should be used to dissolve the samples prior to spotting?

d. How are the spots visualized after developing the TLC plate?

e. Which information can the student gather from the TLC?