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Meeting #12
General Announcements (please read since you will held responsible for the content!)
1. Quiz 6
The next quiz will be administered on November 7, 2013 at 12 pm. It will cover the Grignard reaction and the esterification. Make sure that you show up on time. Otherwise you will not be allowed to take the quiz.
2. Research project
Please start looking for a partner for the Ferrocene project. Your partner should ideally be in a different time slot than yourself i.e., if you are in the T/R afternoon section, you will have to find somebody in the W/F afternoon section. This way nobody has to put in additional time outside their regular schedule, which means that each group has four lab meetings to complete the project. We have to avoid as much as possible to have 20+ students running around in the lab (Safety!).
3. Experimental Hints
a. For the esterification it is crucial that the benzoic acid used is VERY dry. It is also very important that the mixture is refluxed properly during the esterification. Otherwise, the yield of the ester will be very low.
b. The nitration mixture concentrated nitric acid and concentrated sulfuric acid (HNO3:H2SO4=1:1) will be provided from lab support.
c. The nitration has to be carried out at low temperatures (T= ~0 oC). This is accomplished by using a proper ice-bath (huh?).
d. Make sure to submit a GC/MS sample as well (solvent: ethyl acetate. conc: 1 mg/mL).
e. If possible both reactions (esterification and nitration) should be carried out during meeting 12. This will give you more time to recrystallize the final product and get better quality crystals. The final product has to be turned in to the TA by Friday, November 8, 2013 at 5 pm. Late submission will not receive any credit. Sorry! :-(
4. Safety
a. Concentrated nitric and concentrated sulfuric acid are very corrosive already individually. The nitration mixture used in the lab is even worse. It causes major skin damage and acid burns that heal very poorly. Any direct contact with them has to be avoided.
b. The diethyl ether (in the esterification experiment) is removed using the rotary evaporator. It is also important to remove the methanol because it will react with the nitration mixture as well.
5. Report for Grignard project
The postlab report for this project is due on November 19 or November 20, 2013. The report has to be written in the lab notebook and be submitted to the TA.
Homework questions (due on 11/5/2013 or 11/6/2013)
1. Referring to the esterification carried out in the lab, answer the following questions. Show balanced chemical equations and key intermediates where appropriate.
a. The instructor emphasized that water has to be excluded from the reaction. What are the source of water here?
b. Concentrated sulfuric acid is used as catalyst in this reaction. Why is it not as efficient as one would expect?
c. Why is it important to reflux the reaction mixture very well?
d. After the reflux is completed, the reaction mixture is chilled before ice-cold water is added. Which purpose does the addition of water serve? What does the student observe here?
e. Why is the aqueous layer obtained in d. extracted with diethyl ether?
f. The combined organic layers are extracted with saturated sodium bicarbonate solution. How does the student know that he is done with this step?
g. The student obtains an infrared spectrum for the product. How is this spectrum acquired?
2. Referring to the nitration reaction carried out in the lab, answer the following questions. Show balanced chemical equations where appropriate.
a. What is the electrophile in the reaction? How is it obtained in the reaction?
b. Which temperature is the student looking for during the nitration?
c. After the reaction is completed, the reaction mixture is poured over ice. Which purpose does this step serve?
d. A student recrystallizes the crude product from methanol:water (1:4). What would he observe?
e. The mass spectrum of the crude product displays three peaks that are very close together. All display the same molecular ion peak. Rationalize this observation.