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. Why has water to be excluded from the reaction as much as possible. How is this accomplished (three ways)? Show pertinent equations.

b. Why is the Grignard reagent chilled in an ice-bath in the initial stages of the reaction?

c. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture. Which precaution have to be taken here? Show pertinent equations.

d. A student obtains an oily residue as crude product. Which conclusion can he draw and how should he proceed?

e. In order to recrystallize the crude, a student dissolves it in petroleum ether at room temperature, and then places the solution in an ice-bath. What would he observe?

f. What is the melting point of the final product?

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, diethyl ether, and isopropanol. 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 choses one of the solvents above and observes that the Rf-values are low (Rf<0.2) for all compounds. Which solvent did you most likely pick and what can he do to improve the situation?

c. In the experiment, which compounds should be spotted on the TLC plate?

d. How are the spots visualized? Which precautions have to be taken here?