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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 13, 2014 at 11 am. It will cover the Grignard 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 Wednesday, November 12 and Thursday, November 13, 2014. There will be no lab meeting on Friday, November 14, 2014 starting at 1 pm. However, the instructor will have a demonstration on the GC/MS and the HPLC equipment.
4. Experimental Hints
a. For the esterification it is crucial that the benzoic acid used is VERY dry. Place the benzoic acid under the heating lamp for 15 minutes before starting the reaction.
b. It is also very important that the mixture is refluxed properly during the esterification. This means that the mixture has to boil and that a reflux ring is observed in the condenser. Otherwise, the yield of the ester will be very low.
c. The nitration mixture concentrated nitric acid and concentrated sulfuric acid (HNO3:H2SO4=1:1) will be provided from lab support.
d. The nitration has to be carried out at low temperatures (T= ~0 oC). This is accomplished by using a proper ice-bath (huh?).
e. Make sure to submit a GC/MS sample as well (solvent: ethyl acetate. conc: 1 mg/mL). The NMR sample is dissolved in CDCl3 (50-100 mg/mL).
f. 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 Wednesday, November 19, 2014 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 25 or November 26, 2014. The report has to be written in the lab notebook and be submitted to the TA.
Homework questions (due on 11/12/2014 or 11/13/2014)
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. The student reacts the 1.5 g of the benzoic acid with 4 mL of methanol. The literature reports an equilibrium constant of Keq=2.3. Determine the yield (in percentage and grams) for the reaction. What would the yield be if the acid contained 10 % of water?
b. What is used as the catalyst in this reaction? Show the key intermediate.
c. Why is it important to reflux the reaction mixture very well? What does this mean?
d. After the reflux is completed, the reaction mixture is chilled. The student observes a copious amount of solid in the flask. Rationalize this observation. How should the student proceed?
e. Why is it advisable to use a centrifuge tube instead of a separatory funnel for the extractions?
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. What are the key peaks in the infrared spectrum to observe for the product?
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. Why is it very important to control the temperature properly? Which temperature is the student looking for?
c. After the reaction is completed, the reaction mixture is poured over ice. Which purpose does this step serve?
d. A student attempts to recrystallize the crude product from methanol. What would he observe?
e. What are the key changes in the infrared spectrum going from methyl benzoate to methyl m-nitrobenzoate?
Computational assignment (Part 4 of the project)
Using SPARTAN, determine the energy for the three intermediates (cation formed in the ortho, the meta and the para attack) for the nitration of anisole and the three intermediates for the nitration of nitrobenzene. Like before, use 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. Make sure to account for the probability in your calculations.)
Include the data and the analysis into the postlab report for this project.