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.
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. Why is the entire setup assembled first before placing the flask in the ice-bath?
b. What is the proper placement and use of the rubber septum?
c. Why is the flask placed in an ice-bath at the beginning of the reaction and after the reaction?
d. After the reaction is completed, chilled 10% sulfuric acid is added slowly. Rationalize this step.
e. A student forgot to extract the organic layer with sodium bicarbonate solution afterwards. What would he observe?
f. What is petroleum ether and why is it used in this reaction?
g. A student observes a melting point of 98-102 oC after the first recrystallization. Which conclusion can he draw from this observation and how should he proceed?
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, propanol, dichloromethane and toluene. 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. 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 prior to spotting?
d. Why is a UV-lamp used to visualize the spots?