last updated Tuesday, February 13, 2007

Problem set  Meeting 12 

Announcement

1. The instructor will offer an in-lab demonstration of the Grignard setup on February 14, 2007 at 4:00 pm and 4:30 pm in YH6086.

2. The final version of the paper is due on February 16, 2007 at 5 pm in YH3077E. Make sure that you turn it in online by February 20, 2007 at 10 pm.

3. The next quiz will be administered on February 15, 2007 at 12 pm. It will cover step 3 of the lidocaine project, NMR and MS spectroscopy.

Questions

1. Referring to the Grignard reaction, answer the following questions. Show chemical equations when appropriate.

a. Why is it necessary to heat the glassware prior to carrying out the reaction?

b. Magnesium is an alkaline earth metal. Which consequences does this have for the reaction?

c. During the reaction, water is kept out of the system by using a drying tube. Draw a sketch of a properly filled drying tube. Where is it placed in the setup?

d. A student is running late with his reaction and adds the ethereal bromobenzene solution within a short period of time. What would he observe?

e. What is the source for the electrophile in this reaction?

f. After the reaction of the Grignard reagent with the electrophile, the reaction mixture is allowed to warm up. Then chipped ice and conc. sulfuric acid are added. Explain briefly.

g. Later on during the work-up, the organic layer is extracted with sodium hydroxide solution. Explain.


2. Theoretical issues

a. Bromides are often used as starting materials to form the Grignard reagents. Which advantages do the have compared to chlorides?

b. Which properties should a solvent have in order to be suitable as a solvent for Grignard reactions?

c. When reacting Grignard reagents with esters, tert. alcohols are obtained as major product. Rationalize this observation.

d. Strictly speaking, the description of Grignard reagents as "RMgX" is not correct. Why?