last updated Tuesday, May 08, 2007

Problem set  Meeting 12 

Announcement

1. The instructor will offer an in-lab demonstration of the Grignard setup on May 9, 2007 at 4:00 pm and 4:30 pm in YH 6086.

2. The final version of the paper is due on May 11, 2007 at 5 pm in YH 3077E in printed version. Make sure that you turn it in online by May 14, 2007 at 10 pm.

3. The next quiz will be administered on May 9, 2007 at 12 pm. It will cover step 3 of the lidocaine project and NMR spectroscopy.

Questions

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

a. Why is it important to exclude water as much as possible during the formation of the Grignard reagent? How is this accomplished?

b. Describe briefly how the joints should be lubricated.

c. How does the student know that the reaction started?

d. What are the consequences of a rapid addition of the ethereal bromobenzene solution?

e. Why is it important to weight the dry-ice right before it is needed and not 30 minutes prior?

f. During the workup, sulfuric acid is added. Explain.

g. Why is the organic layer extracted with sodium hydroxide solution?

2. Theoretical issues

a. A student has to prepare a Grignard reagent and can choose from the following compounds: fluoropentane, bromopentane, pentanol and iodopentane. Which one should he use? Rationalize your choice.

b. Why are ethers are most commonly used as solvents for Grignard reagents?

c. In which way does the age of the magnesium metal used in the reaction influence the outcome?

d. Why is the decription of Grignard reagents as "RMgX" strictly speaking wrong, particularly in solution?