last updatedThursday, November 09, 2006
Problem set Meeting 12 Announcement
1. The instructor will offer an in-lab demonstration of the Grignard setup on Monday November 6, 2006 at 4:00 pm in YH6086.
2. The final version of the paper is due on November 9, 2006 at 5 pm in YH3077E. Make sure that you turn it in online by November 13, 2006 at 10 pm.
3. The next quiz will be administered on November 6, 2006 at 12 pm. It will cover step 2 and step 3 of the lidocaine project.
Questions
1. Referring to the Grignard reaction, answer the following questions. Show chemical equations when appropriate. a. Where should the setup for the reaction be clamped? b. Why does the procedure suggest to crush up the magnesium turnings in the beginning? c. Why is it necessary to heat the glassware prior to carrying out the reaction?
d. Even though a student prepares his glassware properly, the reaction does not initiate upon addition of the the bromobenzene solution. What should he do to initiate the reaction? (Hint: Praying is not the answer here! :-))
e. The etheral bromobenzene solution has to be added slowly. Why?
f. Why is it unwise to weigh the dry ice significantly before it is needed?
g. Outline a separation scheme for the isolation of the product, starting from the point the dry ice was added.
2. Theoretical issues
a. Most aryl iodides are more reactive than the corresponding aryl bromides. Rationalize this observation. Why are they not used in the lab to prepare the Grignard reagent?
b. Which properties does a solvent have to have in order to be suitable as a solvent for Grignard reactions?
c. Grignard reagents underly the Schlenk equilibrium. What does this mean?