Meeting 8/9 Problem Set
ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up
1. Referring to the Grignard reaction, answer the following questions.
a. Why does water pose a problem in the reaction?
b. The solution of the Grignard reagent is placed in an ice-bath while adding the benzoin solution. Rationalize this step.
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. During the work-up, a student is asked to add 10% sulfuric acid to the reaction mixture. Show pertinent equations. Which precaution have to be taken here?
e. The crude product is recrystallized from hot petroleum ether. Rationalize the choice of solvent. Which precautions have to be taken here?
f. The reaction leads to two products in a ratio 97:3. Explain briefly why by showing appropriate intermediate.
2. Referring to the TLC part of the experiment, answer the following questions.
a. Assume that the following solvents are provided in the lab: hexane, toluene, propanol and dichloromethane. Which single solvent would be most suitable for the TLC in order to accomplish a good separation between the product and the reactant?
b. A student uses toluene as solvent and observes that all Rf-values are fairly low. In addition, the separation of the compounds on the plate is very poor. What can he do to improve the separation?
c. Which compounds should be spotted on the TLC plate in the lab?
d. How are the spots visualized?
3. Which of the following solvents is suitable for Grignard reactions? Explain briefly why or why not. Show a chemical equation where appropriate.
a. n-propylamine
b. acetone
c. 1,2-dimethoxyethane