last updated Thursday, February 15, 2007

Meeting #13

General Announcements

1. The next quiz will be administered on Thursday, February 22, 2007 at 12 pm. It will cover the Grignard reaction, esterification and nitration reaction.

2. Please look start looking for a partner for the last project. Your partner should be in a different time slot than yourself e.g. 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. The proposal will be due on March 2, 2007 at 5 pm.

3. If possible both reactions (esterification and nitration) should be carried out in this lab. This will give you more time to recrystallize the final product and get better quality crystals.

Homework questions

1. Esterification

a. Why is it imperative to dry the benzoic acid thoroughly before carrying out the esterification?

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

c. What is the function of the sulfuric acid in this reaction? Show appropriate intermediates here.

d. The etheral layer is extracted with sodium bicarbonate during the work-up process. Explain and show pertinent equations.Which precautions have to be taken here?

2. Nitration reaction

a. Why is it important to dissolve the ester in conc. sulfuric acid before adding the nitration mixture?

b. Why is the reaction mixture placed in an ice bath?

c. A student attempts to recrystallize the crude product from a mixture of water and methanol (4:1). What would he observe?

d. What are the most important changes in the IR spectrum going from methyl benzoate to m-nitro methylbenzoate?

3. Theory of electrophilic substitution reactions

a. When performing a nitration reaction of toluene, the amount of the ortho product is larger than the amount of para product. However, if a bromination is carried out, the situation reverses. Explain briefly.

b. How can one predict where an incoming electrophile will go preferentially if there are already two substituents on the ring?