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Grignard Reaction Experiment: Formation of Organometallic Compounds

• Magnesium turnings
• Iodine crystals (a small amount, used as an initiator)
• Diethyl ether (anhydrous)
• Methyl iodide
• Benzophenone
• Hydrochloric acid (10% solution)
• Sodium hydroxide solution (10%) (for washing, if needed)
• Anhydrous sodium sulfate (drying agent)
• Phenolphthalein indicator (optional, for base wash monitoring)
• Round-bottomed flask
• Condenser
• Thermometer
• Magnetic stirrer and stir bar
• Separatory funnel
• Dropping funnel
• Ice bath
• Rotary evaporator (for solvent removal)
• Appropriate recrystallization solvent (e.g., ethanol, hexanes)

1. Preparation of Grignard Reagent:
   1. In a dry round-bottomed flask, add magnesium turnings and a very small crystal of iodine.
   2. Attach a condenser to the flask and slowly add anhydrous diethyl ether. The apparatus should be assembled to prevent atmospheric moisture from entering.
   3. Heat the mixture gently while stirring with a magnetic stirrer until the magnesium begins to react (indicated by a cloudy suspension and possibly a slight exotherm). This may require some initiation; gentle warming may be needed.
   4. Once the reaction starts (evidenced by visible reaction), add methyl iodide dropwise using a dropping funnel, controlling the rate of addition to manage the exotherm.
   5. Continue stirring until the Grignard reagent (methylmagnesium iodide) is formed (indicated by a clear or slightly cloudy solution, depending on concentration). The reaction is exothermic.
2. Reaction with Benzophenone:
   1. To the Grignard reagent solution, slowly add a solution of benzophenone dissolved in anhydrous diethyl ether. Keep the solution cool during addition.
   2. Monitor the temperature during the addition to ensure it remains below 0°C (use an ice bath if necessary) to prevent side reactions and decomposition of the Grignard reagent.
   3. Continue stirring for 1-2 hours, allowing the reaction to complete. The reaction may be monitored using standard techniques.
3. Hydrolysis and Product Isolation:
   1. Carefully add ice-cold hydrochloric acid (10% solution) to the reaction mixture slowly to neutralize the Grignard reagent and protonate the alkoxide intermediate. This step is exothermic.
   2. Stir vigorously until the reaction mixture separates into two layers (aqueous and organic).
   3. Transfer the organic layer to a separatory funnel.
   4. Wash the organic layer with water, then with the 10% sodium hydroxide solution (to remove any remaining acid), and finally with water again to remove residual base.
   5. Dry the organic layer over anhydrous sodium sulfate.
   6. Evaporate the ether using a rotary evaporator to obtain the crude product (triphenylmethanol).
   7. Recrystallize the crude product from a suitable solvent (e.g., ethanol/water, or hexanes) to purify it.

• Preparation of Grignard reagent: This involves the reaction of magnesium with an alkyl halide (methyl iodide in this case) in the presence of a suitable solvent (diethyl ether). This is highly sensitive to moisture and oxygen.
• Reaction with carbonyl compound: The Grignard reagent reacts with benzophenone (a carbonyl compound) to form a tertiary alcohol (triphenylmethanol).
• Hydrolysis and product isolation: The reaction mixture is hydrolyzed using hydrochloric acid, and the product is extracted, washed, dried, and purified.

• This experiment demonstrates the synthesis of organometallic compounds, specifically Grignard reagents, and their reactivity with carbonyl compounds.
• Grignard reagents are versatile reagents used in various organic synthesis reactions, including the formation of carbon-carbon bonds.
• The experiment showcases the importance of organometallic compounds in organic chemistry and their applications in the synthesis of complex organic molecules.