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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 February
17, 2015 at 9 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 Thursday,
February 12 and Friday, February 13, 2015.
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. The students will use the propylene glycol filled condenser for this task again.
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. The student will have to submit a HPLC sample for the crude nitration product (solvent: isopropanol, conc: 1 mg/mL)
f. 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.
g. 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,
February 18, 2015 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
February 24 or February 25, 2015. The report has to be written in the lab notebook and be submitted to the TA.
Homework questions (due on 2/12/2015 or 2/13/2015)
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. The student reacts the 1.0 g of the benzoic acid with 5 mL of methanol. The literature reports an equilibrium constant of Keq=2.5. Determine the yield (in percentage and grams) for the reaction. What would the yield be if the acid contained 5 % 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? Which observations should the student make?
d. Why should the student use a centrifuge tube rather than a separatory funnel for the extraction steps?
f. The combined organic layers are extracted with saturated sodium bicarbonate solution. How does the student know that he is done with this step?
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. 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. Which compounds does the crude product contain? How does the student determine if the proposed compounds are present?
e. How is the crude product purified?
f. How should the final product look like?
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 N,N-dimethylaniline and the three intermediates for the nitration of benzaldehyde. 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 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.