Meeting 8 Problem Set

Announcements:

1. The Grignard project will take about 1.5 lab periods. This means that most of the students will finish up the project during meeting 9. In addition, there will be also an NMR lab during this meeting which is also mandatory.

2. Final exam/Review

The final exam will take place on Thursday, September 9, 2010 from 9-12 pm in Boelter 3400. The instructor will offer a review session on Tuesday, September 7, 2010 from 5-6:50 pm in YH 2200.

3. Experimental

a. If you receive a two-necked or three-necked flask instead of a simple round bottom flask, you do not need to use a Claisen adapter in your setup anymore because you have enough outlets already. If you break the round bottom or two/three-necked flask, you will receive an automatic zero for the lab because it shows carelessness. In addition, you will have to pay for the damage!

b. In lab, please use 10 mL of tetrahydrofuran instead of 7 mL of dichloromethane as the solvent for the benzoin. We are not allowed to use dichloromethane in the lower division labs anymore. Please make sure that you keep the THF bottle closed whenever possible since THF is very hygroscopic.

c. The lab support will provide 3 M MeMgBr solution instead of 1.4 M MeMgBr solution.

4. No online-quiz this time!

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. Water should be excluded from the reaction as much as possible. Why is this very important here?

b.What is the function of the drying tube in the setup? How is it properly packed? Show a diagram.

c.Why is the reaction mixture cooled when the benzoin solution is added?

d. After the reaction mixture from c. was refluxed, 10% sulfuric acid is added. Which purpose does this step serve and which precautions have to be taken here?

e. The combined organic layers are extracted with sodium bicarbonate solution. Why is this necessary here?

f. High-boiling petroleum ether is used ether for the recrystallization step. Rationalize this choice.

g. Why is it important that the solution is not placed in an ice-bath during the recrystallization step?

h. Which information does the student gather from the GC spectra of the crude and the final product?

i. Where are the GC spectra available?