Meeting 8/9 Problem Set
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.
a. Water should be excluded from the reaction as much as possible. How is this accomplished? Show pertinent equations.
b. Based on the quantities given in the reader, what is the ratio of Grignard reagent to benzoin? Show calculations.
c. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture. Show pertinent equations. Which precaution have to be taken here? Could concentrated sulfuric acid acid be used instead?
d. The student adds an excessive amount of MgSO4 to the organic layer. Which problem is he going to face?
e. Student A obtains an oily residue as crude product. How should he proceed?
f. Student B uses diethylether as solvent for the recrystallization. What would he observe?
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, acetone, and dichloromethane. Which single solvent would be most suitable for the TLC in order to accomplish a good separation between the product and the reactant?
b. Student C uses toluene as solvent and observes that the Rf-values are pretty low and that the separation of the compounds on the plate is pretty poor. What can he do to improve the separation?
c. Which compounds should be spotted on the TLC plate?
d. How are the spots visualized?
3. Which of the following solvents is suitable for Grignard reactions? Explain briefly why or why not.
a. Acetone
b. Hexane
c. 1,2-Dimethoxyethane
d. Ethyl acetate