Synthesis of triphenylcarbinol from benzophenone and phenylmagnesium bromide
The setting and execution of the reaction are as follows (if the reaction is too violent, prepare an ice bath to cool the solution):
Weight 1.00 g magnesium turning
Put Mg into a dry 100ml round bottom flask with a flap shaped stirring rod.
In the separation funnel connected to the side arm of the Clarison connector,
Add 4.5 mL (6.75 g) of dry (anhydrous; from newly opened bottles) bromobenzene
Add 8 ml of anhydrous ether from the container just opened (after opening the ether, make sure that the back cover is tight after taking out the ether).
Rotate to mix the liquid in the flask
Add about 1-2 ml of bromobenzene/ether solution to the round bottom flask.
Turbidity and bubbles on the metal surface indicate that the reaction has started. This may take 5-10 minutes. If there is no obvious reaction after 10 minutes, add some small iodine crystals. If the reaction is still not started, consult the coach and you may need to start again.
Once the reaction starts, open the cooling water of the condenser and start the agitator. Slowly add the remaining bromobenzene/ether solution and drop it in order to maintain stable reflux. Too fast addition may lead to the formation of diphenyl (drawing the structure and predicting the reaction mechanism). It takes about 45 minutes to add bromobenzene solution. After adding the bromobenzene solution, rinse the adding funnel with an additional 3ml of anhydrous ether, and add the rinsing solution to the round bottom flask.
Install the flask into the heating hood and gently reflow for 15 minutes. The final Grignard mixture should be turbid and most of the magnesium metal should disappear. Cool the mixture to room temperature, and then add enough anhydrous ether into the reaction flask to make its final volume about 40ml. Grignard reagent must be used immediately after cooling.
Grignard reagent is used in the two reactions described in Part A and Part B, and about half (about 20 ml) of newly prepared phenylmagnesium bromide (Grignard reagent) is used in each reaction (accurate measurement in a graduated cylinder is not required).
Grignard reagent must be used on the day when it is ready, and the first day of each experiment must be conducted on the same day when Grignard reagent is made.
Part A: synthesis of triphenylcarbinol from benzophenone and phenylmagnesium bromide
The reaction of phenylmagnesium bromide with benzophenone is shown in the figure below. This reaction, like the reaction to produce benzoic acid, must be completed on the first day and immediately after Grignard reagent is ready.
Preparation of triphenylmethane.
Dissolve 2.00 g (~11.0 mmol) of benzophenone in 15 mL of anhydrous ether, and put it into a clean and dry 100 mL round bottom flask with a flip top stirring rod. Place the round bottom flask on the stirring hot plate (do not heat it), and stir until all solid benzophenone is dissolved.
Attach a Clayson adapter. Place a condenser column in a straight line above the round bottom flask into the Clausen adapter.
Place a separation funnel containing 15 ml of phenylmagnesium bromide (tetrahydrofuran) into the side arm of the Clayson adapter.
