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, do not use 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. In addition, you will have to pay for the damage!
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. Like often in this lab course, water is a problem in this reaction. How does the student ensure that the amount is minimized in this reaction?
b. Why is the round-bottomed flask placed in an ice-bath at the beginning of the reaction? Which precautions have to be taken here?
c. After the reaction is completed, chilled 10% sulfuric acid is added slowly. Rationalize this step.
d. Next, the organic layer is extracted with sodium bicarbonate. Explain briefly.
e. Why is it important to minimize the amount of MgSO4 used here?
f. High-boiling petroleum ether is used as solvent for the recrystallization. Rationalize this choice.
g. Why is the solution not placed in an ice-bath during the recrystallization?
2. Referring to the TLC part of the experiment, answer the following questions.
a. Assume that the following solvents are provided in the lab: petroleum ether, methanol, dichloromethane 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. A student uses ethyl acetate as solvent and observes that all Rf-values are fairly high. In addition, the separation of the compounds on the plate is very poor. What can he improve the separation?
c. Which compounds should be spotted on the TLC plate in the lab?
d. Which solvent should be used to dissolve the samples prior to spotting?