CHEM 344 - Lab Report #6-7

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Apr 3, 2024

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Olivia Dobson CHEM 344-03 02/21/2023, 02/28/2023 Lab #6/7 Grignard Reaction: Synthesis of Triphenylmethanol Objectives: To prepare a Grignard reagent from bromobenzene and magnesium; To perform a reaction using strictly anhydrous conditions; To perform a reaction in situ to preserve the Grignard reagent formed in the previous reaction; To characterize a product using melting point determination, 1 H NMR spectroscopy, 13 C NMR spectroscopy, IR spectroscopy, and thin-layer chromatography.

Overall Reaction Mechanism *Note: the benzophenone can also be shown with a partial positive on the carbon and partial negative on the oxygen, as in post-lab question 2*

Stoichiometry – Reaction 1 Reaction 1 Compound Amount Molar Mass (g/mol) Density (g/mL) mmol Molar Equiv. Bromobenzene 0.75 mL 157.01 1.5 7.17 1.16 Magnesium 0.150 g 24.305 1.74 6.17 1 Limiting Reagent : Magnesium Theoretical Yield : 1.12g phenylmagnesium bromide Stoichiometric Calculations – Reaction 1 1.) mmol: Bromobenzene: 0.75𝑚𝐿 𝑥 1.5 𝑔 1 𝑚𝐿 𝑥 1 𝑚𝑜𝑙 157.01 𝑔 𝑥 1000 𝑚𝑚𝑜𝑙 1 𝑚𝑜𝑙 = 7.17 𝑚𝑚𝑜𝑙 Magnesium: 0.150𝑔 𝑥 1 𝑚𝑜𝑙 24.305 𝑔 𝑥 1000 𝑚𝑚𝑜𝑙 1 𝑚𝑜𝑙 = 6.17 𝑚𝑚𝑜𝑙 2.) Molar Equivalents: Bromobenzene: 7.17 𝑚𝑚𝑜𝑙 𝑏𝑟𝑜𝑚𝑜𝑏𝑒𝑛𝑧𝑒𝑛𝑒 6.17 𝑚𝑚𝑜𝑙 𝑚𝑎𝑔𝑛𝑒𝑠𝑖𝑢𝑚 = 1.16 3.) Theoretical Yield: 6.17 𝑚𝑚𝑜𝑙 𝑚𝑎𝑔𝑛𝑒𝑠𝑖𝑢𝑚 𝑥 1 𝑚𝑜𝑙 1000 𝑚𝑚𝑜𝑙 𝑥 1 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 1 𝑚𝑜𝑙 𝑚𝑎𝑔𝑛𝑒𝑠𝑖𝑢𝑚 𝑥 181.31 𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 1 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 = 1.12𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

Stoichiometry – Reaction 2 Reaction 2 Compound Amount Molar Mass (g/mol) Density (g/mL) mmol Molar Equiv. Phenylmagnesium bromide 1.12 g 181.31 1.14 6.18 1.03 Benzophenone 1.094 g 182.217 1.11 6.004 1 Limiting Reagent: Benzophenone Theoretical Yield: 1.56 g triphenylmethanol Stoichiometric Calculations – Reaction 2 1.) mmol Phenylmagnesium bromide: 1.12 𝑔 𝑥 1 𝑚𝑜𝑙 181.31 𝑔 𝑥 1000 𝑚𝑚𝑜𝑙 1 𝑚𝑜𝑙 = 6.18 𝑚𝑚𝑜𝑙 Benzophenone: 1.094 𝑔 𝑥 1 𝑚𝑜𝑙 182.217 𝑔 𝑥 1000 𝑚𝑚𝑜𝑙 1 𝑚𝑜𝑙 = 6.004 𝑚𝑚𝑜𝑙 2.) Molar Equivalents: 6.18 𝑚𝑚𝑜𝑙 𝑝ℎ𝑒𝑛𝑦𝑙𝑚𝑎𝑔𝑛𝑒𝑠𝑖𝑢𝑚 𝑏𝑟𝑜𝑚𝑖𝑑𝑒 6.004 𝑚𝑚𝑜𝑙 𝑏𝑒𝑛𝑧𝑜𝑝ℎ𝑒𝑛𝑜𝑛𝑒 = 1.03 3.) Theoretical Yield: 6.004 𝑚𝑚𝑜𝑙 𝑏𝑒𝑛𝑧𝑜𝑝ℎ𝑒𝑛𝑜𝑛𝑒 𝑥 1 𝑚𝑜𝑙 1000 𝑚𝑚𝑜𝑙 𝑥 1 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 1 𝑚𝑜𝑙 𝑏𝑒𝑛𝑧𝑜𝑝ℎ𝑒𝑛𝑜𝑛𝑒 𝑥 260.33 𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 1 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 = 1.56 𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

Procedure Procedure Observations 1. The apparatus was set up in the following way: A Claisen head adapter was placed in a 10mL r.b. flask and clamped to the ring stand. A drying tube filled with cotton and CaCl 2 was attached to the Claisen head. A rubber septum was placed in the top of the Claisen head.  Glassware placed in the oven for ~10 minutes 2. 150mg of magnesium ribbon was weighed out. It was polished, cut into small pieces, and then quickly added to the reaction flask (reattaching the Claisen head after). The stirrer/hot plate was placed 2-3 inches below the r.b. flask.  0.150g magnesium strip obtained from TA  Cut into very small pieces 3. A dry centrifuge tube was obtained from the oven and allowed to cool. A calibrated Pasteur pipet from the oven was used to add 700 μ L bromobenzene to the centrifuge tube. 3.0mL anhydrous ether was added using a provided syringe or a clean, dry Pasteur pipet. The vial was sealed with a rubber septum to prevent moisture from contaminating it.  ~750 μ L added with a calibrated Pasteur pipet

4. A clean, dry 1.0mL plastic syringe fitted with a metal needle was used to draw up 0.8mL bromobenzene solution. The syringe needle was inserted through the reaction apparatus’s rubber septum, and the bromobenzene was added to the magnesium turnings with gentle stirring. The solution was heated if it did not turn a brown/gray color and bubbles (indicating phenyl magnesium bromide formation). No additional bromobenzene solution was added until the reaction was started.  The reaction started rapidly – within a couple of minutes  The solution turned brown, and the magnesium looked darker  A small aliquot of the reaction solution was given to a lab table mate to jumpstart his reaction  No heating was required 5. If the reaction still was not started, the following methods were employed: a.) a crystal of iodine was added to the flask and then heated gently b.) the Claisen head was detached, and the mixture was ground against the glassware walls using a dry, flat-headed stir rod with gentle heating c.) s small aliquot of the reaction solution and a few Mg turnings were removed from the flask and placed in a dry test tube. A glass stir rod was used to grind the turnings. The solution/turnings were transferred back into the main vessel if the reaction started.  None of the mentioned techniques were needed

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