last updated Thursday, May 06, 2010

Meeting #13

General Announcements (please read since you will held responsible for the content!)

1. Quiz 6

The next quiz will be administered on Tuesday, May 11, 2010 at 12 pm and will cover the entire Grignard project (Grignard, esterification, nitration). Make sure that you show up on time. Otherwise you will not be allowed to take the quiz.

2. Research project

Please look start looking for a partner for the last project. Your partner should be in a different time slot than yourself i.e. if you are in T/R morning section, your partner should be in section in the T/R afternoon section or in the W/F afternoon section. We want to avoid as much as possible to have 20+ students running around in the lab (Safety!)

3. Experimental

a. It is important the the reaction mixture is refluxed properly during the esterification.

b. The nitration has to be carried out at low temperatures (0 ^oC). This is accomplished by using a proper ice-bath.

c. If possible both reactions (esterification and nitration) should be carried out during meeting 13. 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 May 14, 2010. Late submission will not receive any credit. Sorry! :-(

4. Safety

a. Concentrated nitric and concentrated sulfuric acid are very corrosive 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. Diethyl ether is removed using the rotary evaporator.

5. Report for Grignard project

The postlab report for this project is due on May 25 or May 26, 2010.

Homework questions

1. Referring to the Esterification carried out in the lab, answer the following questions. Show chemical equations and key intermediates where appropriate.

a. Why is it imperative that the benzoic acid is as dry as possible for the reaction? How is this accomplished?

b. Why is methanol used in excess in this reaction?

c. Why is it necessary to reflux this mixture? What exactly does this mean?

d. After the reflux is completed, the procedure asks to cool the reaction mixture first and then poured it into cold water. What is the purpose of this step?

e. Why are the combined the organic layers extracted with sodium bicarbonate? How does the student know that he is done with this step?

2. Given is the following data (obtained from Spartan calculation (AM1)) for benzoic acic (A), the protonated form of benzoinc acid (B) and the benzoate ion (C). Answer the following questons.

a. Rationalize the differences in the C=O bond and the C-O bond lengths in A and B.

b. Rationalize the differences in the C-C=O bond and the C-O bond lengths in A and B.

c. Which of these species is the the best electrophile? Explain briefly.

3. Referring to the Nitration reaction carried out in the lab, answer the following questions. Show chemical equations where appropriate.

a. The nitronium ion is used as the electrophile in this reaction. How is it obtained in the lab?

b. Why is it important to dissolve the ester in concentrated sulfuric acid prior to introducing the electrophile?

c. The reaction has to be carried out in an ice-bath. Rationalize this step.

d. Why is the reaction mixture poured over ice?