Preparation Of Triphenylmethanol By a Grignard Rea

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Lab 2: Preparation of Triphenylmethanol by a Grignard Reaction Introduction: The Grignard addition of an organomagnesium compound to a carbonyl to form an alcohol is one of the classic reactions in organic chemistry. First, magnesium will be inserted into a carbon-halide bond to form nucleophilic phenylmagnesium halide Grignard reagent. This reaction is an oxidation of the metal converting Mg0 to Mg2+ carried out in anhydrous ether solvent. This process will be done with care due to the moisture sensitivity of the phenylmagnesium halide. Second, methyl benzoate is added to form a new carbon-carbon sigma bond. The intermediate magnesium alkoxide will then be hydrolyzed to form tertiary alcohol product. Experimental Procedure: Part A: Preparing the Grignard reagent • I placed 1.98 grams of magnesium turnings into a cleaned 250mL round-bottom flask and then attached the calcium chloride drying tube into the round-bottom flask • Then, I placed this flask onto a heating mantel and adjust the controller to setting ‘6’. This flask is heated until it was too hot to touch. • After the flask was heated, I removed it from the heating mantel and allowed it to cool to room temperature. • Next, I poured 15mL of absolute ether and 9mL of bromobenzene into the 250mL flask and waited 5 minutes for any reaction. • There were no signs of reaction after 5 minutes; therefore the lab assistant used a glass stirring rod to crush the magnesium in order to get the reaction started. When this was done, the liquid became cloudy, rapidly bubbling, and the color turned rusty red. • Next, I added 25mL of absolute ether and attached a reflux condenser to the flask. I turned on the water when I saw ether vapor had successfully wet the joint at the top of the condenser. • Every 60 seconds, I swirled the flask and I continued to perform this action until I saw that the reaction

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