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. The procedure asks to exclude water as much as possible. Explain briefly why and how is this accomplished?
b. Why should the round bottomed flask not be placed in an ice-bath while before the entire setup is assembled?
c. Draw a sketch of a properly filled drying tube. Where is it placed in the setup?
d. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture. Which precaution have to be taken here?
e. Why is the organic layer extracted with sodium bicarbonate solution?
f. The crude product is recrystallized from hot petroleum ether. Rationalize the choice of solvent. 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: petroleum ether, methanol, acetone 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 methanol 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 do to improve the separation?
c. Which compounds should be spotted on the TLC plate in the lab? Which solvent should be used?
d. How are the spots visualized?