Question

Based on the grinard reagent/reaction (preparation of triphenylmethanol).

4. If you don't oven-dry your glassware or use a drying tube, what byproduct will you produce? Illustate its formation by a chemical reaction.

5. You have air-dried your glassware and used a drying tube during the experiment. However, you used a wet methyl benzoate would the byproduct formed be different from that of question 4 above? Explain your answer.

6. Triphenylmethanol (the final product to be obtained during this experiment) can also be prepared by the reaction of PhMgBr with diethylcarbonate (CH3CH2O)2C=O, followed by H+ workup. Draw the corresponding chemical reaction, and explain your answer.

Answer 1

4) The following questions are referring to the preparation of triphenylmethanol by grignard reagent. At this point in the reaction, byproducts are or can be formed when the phenylmagnesium bromide is formed. I know the generic reaction for the byproduct for the first question is R-MgX + H₂O R-H + HO-Mg-X . So, I got specifically for our reaction.

Ph-MgBr + H₂O Benzene + HO-Mg-Br.

or

The reaction should remain free of water, liquid or vapor, because even small amounts of water can destroy the Grignard reagent.

R-MgBr + H₂O --> R-H + MgBrOH

Oven-drying of glassware prior to use is an important technique to ensure that your glassware is dry.

Use of a drying tube is important so that moisture will be trapped with the drying agent before it can enter the reaction flask.

Use of an addition funnel is another important technique that allows addition of reagents without opening the reaction flask to the atmosphere .

A drying tube is a piece of glassware filled with drying agent such as anhydrous calcium chloride. It is fitted to the top of the reaction apparatus so that the reaction is not directly in contact with any moisture in the atmosphere. This helps to keep water away from the reaction mixture, which would destroy the Grignard reagent.