Meeting 8 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. Why do you isolate two different products in this week's reaction? Rationalize the relative yields for these products.

2. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture.

a. The lab support only provided conc. sulfuric acid for the experiment. Can he use it for his work-up? Explain briefly.

b. Why is it important to add the acid slowly, especially in the beginning? Show pertinent equations.

3. Referring to the recrystallization of the crude product,

a. the procedure ask you not to place the solution in an ice-bath. Why?

b. a student uses low-boiling petrol ether. What would he observe?

c. Often times the solution turns brown or purple during the recrystallization. Explain briefly.

4. When forming a Grignard reagent from Mg-metal and an alkyl halide, it is imperative to exclude water from the reaction. Explain briefly why.

5. A students is planning a Grignard reaction and checks for solvents available in his lab. He finds iso-propanol, ethyl acetate and dichloromethane in the solvent cabinet. Which one should he choose if any? Explain briefly.

6. TLC analysis is performed in this experiment as well.

a. Which purpose does it serve here?

b. The following solvents are available to the student: methanol, ethyl acetate, hexane (or any mixture of them). Which solvent should he use if he uses TLC plates coated with silica? Rationalize your choice.