Meeting 8/9 Problem Set
Announcements:
1. This week's project will take about 1.5 lab periods. This means that most of the students will finish up the project during week 9. In addition, there will be also an NMR lab during week 9 which is also mandatory.
2. If you receive a three-necked flask instead of a round bottom flask, you will not require a Claisen adapter in your setup. If you break the round bottom or three-necked flask, you will receive an automatic zero for the lab because it shows carelessness.
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. A student assembles the round-bottomed flask, the Claisen adapter and the air condenser. He then places the flask in the ice bath. Which observation would he make throughout the reaction?
b. Why are anhydrous dichloromethane and anhydrous diethyl ether used in the reaction?
c. Why has the reaction mixture to be cooled in the beginning of the reaction?
d. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture. What happens in this step and which precautions have to be taken here?
e. Why is the organic layer extracted with sodium bicarbonate solution? Explain briefly why.
f. Why is the crude product recrystallized from high-boiling petroleum ether? Which precautions have to be taken here?
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, ethyl acetate and diethyl ether. Which single solvent would be most suitable for the TLC in order to accomplish a good separation between the product and the reactant?
b. A student uses toluene as solvent and observes that all Rf-values are fairly low (<0.2). In addition, the separation of the compounds on the plate is very poor. What can he do to improve the separation?
c. Which compounds should be spotted on the TLC plate in the lab? Which solvent should be used to dissolve the samples?
d. How are the spots going to be visualized?