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Meeting #12
General Announcements (please read since you will held responsible for the content!)
1. Quiz 6
Quiz 6 will be administered on November 5, 2015 at
11 am. It will cover the Suzuki reaction and the esterification.
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. Administrative Issues
a. The esterification and nitration lab will take place on Tuesday,
November 3 and Wednesday, November 4, 2015. The meeting on November 5
and November 6, 2015 are used to finish up the project.
b. There
will be no lab on Tuesday, November 10, 2015. However, the instructor
will offer a GC/MS and HPLC demonstration in the instrumentation room
starting at 2 pm. The lecture will take place as usual.
4. Experimental Hints
a. For the esterification it is crucial that the phenol is dry. It might be advisable to place it under the heating lamp for a couple of minutes (without melting it of course).
b. It is also very important that the mixture is heated properly during the esterification. Otherwise, the yield of the ester will be very low. The students will use the propylene glycol filled condenser for this task again, just in case the mixture reacts more violently than expected.
c. The nitration is a new experiment, which can have a lot of different outcomes. While the nitration system is relatively mild, caution is still necessary because polynitration products are generally very reactive. Any amount of water will be a problem because it would lead to the hydrolysis of the ester. The resulting phenol would be much more reactive and favor the nitration in different positions than the ester.
d. Make sure to submit a GC/MS sample (solvent: ethyl acetate, conc: 1 mg/mL) and a NMR sample (solvent: CDCl3, conc: 50 mg/mL) for the final product.
5. Reports
a. The due date for the lidocaine report is
moved to November 5 and November 6, 2015. Hopefully,
the GC/MS will be up and operational by Tuesday again.
b. The postlab report for the
current project is due on November 12 and November 13,
2015. The report has to be written in the lab notebook and be submitted to the TA.
Homework questions (due on 11/3/2015 or 11/4/2015)
1. Referring to the esterification carried out in the lab, answer the following questions. Show balanced chemical equations and key intermediates where appropriate. Show all calculations.
a. What is used as acid precursor?
b. What is used as the catalyst in this reaction? Show the key intermediate.
c. Why is it important to heat the reaction mixture?
d. Why is the reaction mixture poured into cold water?
e. Which solvent is used for recrystallization? Rationalize the choice.
f. The reaction can leads to O-acylation
or C-acylation product. How could the student distinguish
between these two compounds using infrared spectroscopy?
2. Referring to the nitration reaction carried out in the lab, answer the following questions. Show balanced chemical equations where appropriate.
a. Why is the electrophile in this reaction considered a strong electrophile?
b. How is the electrophile generated in the reaction?
c. After the reaction is completed, the reaction mixture is poured over ice. Which purpose does this step serve?
d. Which compounds does the crude product contain?
e. How is the crude product purified?
Computational assignment (Part 4 of the project)
Using SPARTAN, determine the energy for the five intermediates (cation formed in the 2-, 3-, 2'-, 3'- and 4'-position)) for the nitration of 4-phenylphenol using the AM1 method. Make sure to define the specie as a cation and a multiplicity of singlet. For both cases, answer the following question:
1. Which of the attacks displays the lowest energy for the intermediate? Which one displays the highest energy?
2. What does the energy of the intermediate tell one about the potential product distribution?
3. Using the Arrhenius equation, estimate the relative rates for the different attacks (Hint: Assume that the A-values are the same but make sure to account for the probability in your calculations.)
Include the data and the analysis into the post-lab report for this project.