By: Alexis Huddleston. H Ph Ph OH Ph Summary 1 1 1. Yet, in order to explore the method in which phenylmagnesium bromide and methyl benzoate can react to produce triphenylmethanol, the Grignard reaction was utilized during this experiment. Add 0.5 g of magnesium filings to a large test tube. Step 2: Reflux the solution for an additional 30 minutes. Once the contents of vial #2, which consisted of 1.00 mmol (136.5 mg, 0.1361 g) of methyl benzoate and 1.5 mL of diethyl ether, from the formation of the phenylmagnesium bromide was applied to the round bottom flask, a variety of color changes were noticed. Masterson, Douglas and Tina Masterson. After the mixture has been completely filtered, tightly seal the vial with its cap and allow the product to dry at room temperature. H OH H. Benzene. In order to remove the biphenyl, add 0.5 mL of petroleum ether to the residue, cool in an ice bath briefly while stirring and remove the solvent (process is called trituration). In this experiment, the alkyl magnesium halide will be in the form of phenyl magnesium bromide (R = C6H5in eq. Add the bromobenzene to the large vial containing the ether. Grignard reagents, such as phenylmagnesium bromide, are Lewis bases and are good nucleophiles; they are also good leaving groups. 2. 3) and then benzoic acid is isolated from the acidified reaction mixture (eq. Combine this rinse with the other rinses in the 50 mL Erlenmyer flask. Step 11: Continue refluxing for approximately 10-15 minutes or until nearly all of the magnesium reacts and the solution turns a clear amber color. 2 Mg, ether 2. Step 10: Transfer the remaining contents of vial #1 into the round bottom flask over a 10-minute period. Upon the completion of the formation of triphenylmethanol, the reaction mixture had two layers; the top layer was the product. al. Gently swirl the large vial to mix the contents. Remaining 3.2 mL of bromobenzene mixture was added over 15 minute period. Gently shake the mixture. Thus, it is necessary to apply an extended amount of precaution and effectively keep the reaction free of water; this will most likely result in an increased yield of product and increased accuracy in results. Bromobenzene Phenylmagnesium bromide. The phenyl magnesium bromide will be quenched with solid carbon dioxide (eq. Provide a brief explanation ; and mechanism to explain this observation. Continue refluxing for an additional 3 minutes. Step 3: Get one needle and three 1.0 mL syringes. The phenylmagnesium bromide was prepared in order to begin the reaction and was added to the methyl benzoate. 1), which you will prepare from bromobenzene. Step 6: Use a spatula to add a small piece of iodine crystal through the opening labeled “cap A” on the apparatus. (R = C6H5 in eq. Reagents MW (g/mol) MP (ºC) BP (ºC) Density bromobenzene 157.01 -31 156 1.491 magnesium 24.31 648 1090 carbon dioxide (dry ice) 44.01 -78.5 diethyl ether 74.12 -116 34.6 0.706 Step 8: Dry the diethyl ether organic layer with MgSO4 (magnesium sulfate). Grignard reagents are considered to be organometallic reagents and are therefore usually strong Lewis bases and function as good nucleophiles. Step 4: Use a micropipette to carefully remove the aqueous layer of the solution and transfer it to a clean, dry 50 mL Erlenmyer flask and set it aside. Also, I was able to determine that the percent yield of the product was 24.87%, which indicated that an acceptable yield of triphenylmethanol was synthesized during the experiment. If necessary, add more diethyl ether to the solution. Step 9: Using one of the 1.0 mL syringes, transfer 4-5 drops of the reagent mixture from vial #1 through the septum of “cap A”. Draw all arrows and lone pairs. During the formation of the product, numerous color changes and chemical reactions were noticed, including the formation of bubbles when distilled water was added to the reaction mixture indicating that magnesium was being dissolved. Write A Detailed Mechanism For The Reactions Of Phenylmagnesium Bromide With Methyl Benzoate Which Produced The Conjugate Base Of Triphenylmethanol. Upon synthesizing the final product, the melting point of the product was observed and recorded, allowing the purity of the product to be evaluated. Additionally, the continuation of the Grignard reaction in producing the final product was due to the fact that ketones are more reactive with nucleophiles than esters. Step 4: Place the round-bottom flask into a fume hood and carefully remove “cap A.”. During the experiment, there could have been more precaution taken to ensure that the reaction was free of water. The bromobenzene is reacted with magnesium metal to form phenylmagnesium bromide which is known as Grignard reagent. But this mechanism involves radical intermediates. It is possible that during the process of assembling the microscale apparatus or mixing chemical to form the various reaction mixtures that water vapor was able to settle along the microscale apparatus, thus affecting the production of the triphenylmethanol. Weigh the vial while still tightly sealed with the cap and with the product inside it; record the weight. The melting point and percent yield of the. Step 1: Assemble the microscale apparatus to be used during the preparation of phenyl magnesium bromide. Teixeira, Jennifer M., et al. Step 8: Set the temperature of the hot plate to approximately 90⁰C and reflux the solution in the round bottom flask while stirring for approximately 5 minutes. After 30 minutes the reaction was removed from heat and cooled to room temperature. Step 7: Disassemble the microscale apparatus. The amber colored solution became a darker brown, then changed to a pink color, and finally changed to a peach color. Formation of triphenylmethanol-the product: Step 1: For a 2-minute period, use a second clean syringe to transfer all of the reagent contents of vial #2 through the septum of “cap A” into the round bottom flask. Triphenylmethanol consists of an alcohol group and aromatic bending; according to the peaks in the IR spectrum, the product that was synthesized during the experiment possessed specific functional groups that are present in the structure of triphenylmethanol. Since the melting point range of the product was close to the standard melting point of triphenylmethanol, 160⁰C, it was determined that the product must be considerably pure. a radical anion a radical phenylmagnesium bromide MgBr δ+ δ− 2 Grignard reagents are almost always synthesized in ethereal solvents such as diethyl ether or tetrahydrofuran (THF) for two very important reasons: (1) ethers do not generally react with Grignard reagents (i.e. 1), which you will prepare from bromobenzene. Since Grignard reagents are extremely reactive with Lewis acids such as water, precautions were taken during the lab to ensure that the reaction was not ruined due to the presence of water (Organic Chemistry I and II, 89). Step 15: Clean all glassware and the experimental area.