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Meeting #12
General Announcements (please read since you will held responsible for the content!)
1. Quiz 5
Quiz 5 will be administered on
February 9, 2016 at
9 am. It will cover the entire Lidocaine project.
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
Thursday,
February 11, 2016 and Friday, February 12, 2016. Ideally,
the meeting on February 16, 2016
and February 17, 2016 are used to finish up the project
(characterization, submission of GC/MS and NMR samples). There will be
no prelab for meeting 13.
b. The postlab report
for the lidocaine project has to be written in the lab notebook and
submitted to the teaching assistant. The due dates are February 11,
2016 or February 12, 2016 in your regular lab section. The
report has to be written in the lab notebook and is worth 15 points.
c. The postlab report
for the Suzuki-Esterification-Nitration project has to be written in the
lab notebook and submitted to the teaching assistant. The report for the
project is due on February 23, 2016 or February 24, 2016.
The report has to be written in the lab notebook and is worth 15 points.
4. Experimental Hints
a. It is crucial that the phenol is thoroughlu dried before proceeding with the esterification. 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 relatively 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.
Homework questions (due on 2/11/2016 or 2/12/2016)
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. Why is acetic acid anhydride used instead of glacial acetic acid?
b. What is used as the catalyst in this reaction? Show the key intermediate.
c. Why is it important to reflux the reaction mixture properly? What does this mean in terms of setup?
d. Why is the reaction mixture poured into cold water after the reaction is completed?
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 NMR 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 does the infrared spectrum of the nitro compound differ from infrared spectrum of the ester?
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. Based on the data, answer the following questions:
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.