Meeting 8 (Problem Set)

1. Announcements:

a. The Grignard project will take about 1.5 lab periods. Thus, 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. 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 there are 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! So make sure to clamp the flask properly at the neck.

b. Students will not be allowed to attend a different lab section to finish up their work. This poses a significant safety risk and usually ends up that many sections are entirely overcrowded, which results a very low overall productivity and lots of complaining students.

3. Safety

a. The lab support will provide 3 M MeMgBr solution in diethyl ether. The solution will be dispense by the teaching assistant because the solution is potentially pyrophoric!

b. Tetrahydrofuran, diethyl ether and petroleum ether are very flammable. Do not spill these solvents on the hotplate and keep them away from other ignition sources as well. Any spills have to be immediately cleaned up.

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. After reviewing the chapter about "Polarity" and "Green Chemistry" in the reader, take the online quiz (Extra credit quiz).

(http://bacher.chem.ucla.edu/TakeQuiz/?id=c74d97b01eae257e44aa9d5bade97baf). The quiz is worth 5 points, and has to be taken until one hour prior to the regularly scheduled in-lab meeting 8. Even though you can take the quiz until one hour prior to meeting 8 of your section, you should not delay taking it since there might be some problems with the server. There seem to be problems with some MAC systems as well. After you submit the answers, your score should appear on your screen. If this does not happen, you will have to retake the quiz. (There will not be any possibility to retake the quiz weeks later!). In order to take the quiz, you have to go through a UCLA ICP address. This means that you either have to use your Bruin-Online account or go through the VPN (Virtual Private Network, software can be found here: http://www.bol.ucla.edu/services/vpn/) to have this UCLA ICP address. To log in, use your last name and your student ID. If you are experiencing problems, contact the instructor via email and include your full name (indicated which one is your last name), your student ID and section .

2. Referring to the Grignard reaction, answer the following questions. Show pertinent chemical equations where appropriate.

a. Why is it important to exclude water from the reaction?

b.In the initial stage of the reaction, the Grignard solution is diluted and chilled before the benzoin solution is added. Why is this necessary?

c. A student plans to dissolve his benzoin in diethyl ether. What do you think about this?

d. After the reaction was completed, 10 % sulfuric acid is added to the reaction mixture. Which purpose does the addition of the acid serve? Provide a balanced chemical equation for this step.

e. The student skips the extraction step with sodium bicarbonate solution. What would he observe?

f. Why is it important to remove as much solvent from the organic layer before proceeding with the recrystallization?

g. What is high-boiling petroleum ether? Why is it used in the recrystallization step?

h. Why is the solution not be placed in an ice-bath during the recrystallization?

i. The EI mass spectrum of the final product displays signals at m/z=121 and m/z=107, respectively. Which of these signals is expected to show a higher abundance? Explain briefly why.