Grignard.24Sep2007-1 - Grignard Reaction -...

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Grignard Reaction - Triphenylmethanol Courtesy of Dr. Glenn Nomura With Minor Modifications by Dr. David Jeffrey Reference : Williamson, Macroscale and Microscale Organic Experiments , 5 th edition, Houghton Mifflin: New York, 2007, Experiment 38.4, (1/2 X) macroscale Phenylmagnesium Bromide Grignard reagent, p. 539 Experiment 38.5, (1/2 X) macroscale Triphenylmethanol from Methyl Benzoate, p. 541 Equations: PROCEDURE: (I) Preparation of the Phenylmagnesium Bromide (phenyl Grignard reagent) All precautions should be taken to perform the reaction under dry conditions. Into a clean dry (ungreased) 50 mL round bottom flask is placed 1.0 g (0.0411 g-atom) of magnesium turnings. If convenient, the flask and Mg can be oven dried together for 30 minutes or longer at around 125°C. The 50 mL round bottom flask is removed from the oven and while still hot (CAREFUL!) is connected to a greased clean dry condenser with a cotton ball placed at the top joint to reduce moisture exchange as the glassware cools, or alternatively attach a drying tube filled with fresh Drierite or CaCl 2 using an adapter from the Williamson kit ( Note A ). * 2 nd Reminder: grease all joints thoroughly to prevent seizing of joints and place Keck clips on all ground glass joints. Prepare a cold-water bath (OK to share one bath per hood; icy cold not necessary). Clamp the flask and condenser assembly by the body of the condenser (not by the flask joint). Allow for space beneath the flask for manually raising and lowering the cold water bath. The instructor will next add about 10 mL of dry Et 2 O and 4.5 mL (or 6.71 g) of bromobenzene. Since the Grignard reaction normally will not start on its own, the instructor will come to your hood to press on the Mg turnings with a flattened glass rod. A white turbidity will develop as the Grignard reagent first begins to form. The exothermic formation of Grignard will cause the Et 2 O to reflux rapidly. Allow the reflux to continue at a rapid boil until the Mg has nearly disappeared. The reaction solution will darken to amber as the concentration of PhMgBr builds.
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Grignard.24Sep2007-1 - Grignard Reaction -...

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