Grignard Reagent Preparation Homework

1. What is the limiting reagent in the preparation of the Grignard reagent? Show how you arrived at this conclusion.

2. Why are ether solvents important to the success of the preparation of the Grignard reagent ?

3. Why must the reagents, solvents and apparatus used for the preparation of the Grignard reagent be dry?

4. Why is it necessary to have an ice-water bath available during the preparation of the Grignard reagent?

5. What signs should you look for in determining whether the reaction has been initiated?

6. Why should the bromobenzene not be added all at once to the reaction flask ?

7. Ethanol is often present in the technical grade of diethyl ether. If this grade rather than anhydrous were used, what effect, if any, would the ethanol have on the formation of the grignard reagent ? Explain.

8. Why is it unwise to allow the solution of the Grignard reagent to remain exposed to air for an unnecessary period of time even if it is protected from moisture by drying tubes?

9. Why is it unwise to begin addition of the solution of methyl benzoate to the Grignard reagent before the latter has cooled to room temperature ? Preparation of Triphenylmethanol Homework

1. What is the limiting reagent in the preparation of triphenylmethanol from phenylmagnesium bromide and methyl benzoate ? Show how you arrived at this conclusion. Why do you think this reagent rather than the other was made limiting ?

2. Why must the ester and the diethyl ether in which it is dissolved be anhydrous ?

3. Why is the solution of ester added to the Grignard reagent in a dropwise fashion rather than all at once?

4. Why is saturated aqueous sodium chloride rather than just water used to remove residual sulfuric acid from the organic solution during the workup procedure ?

5. How is unchanged ester removed from the desired product by the workup procedure used ?

6. What happens to any Grignard reagent that remains in the reaction mixture after addition of the ester ?

7. Why should anhydrous rather than technical grade diethyl ether be used to prepare the solution of methyl benzoate that is added to the Grignard reagent ?

8. What is the solid that forms during the addition of the ester to the Grignard reagent?

9. Why does pressure develop when the separatory funnel containing aqueous sulfuric acid and the ethereal solution of organic products is shaken ?

10. Why is the recrystallizing cyclohexane-ethanol (2:1) used instead of either alone?