wittig reaction

Experimental Setup

  • Materials Needed:

    • 10 mL round-bottom flask

    • Hot plate

    • Benzyl triphenyl chloromethane (Benzyl triphenylchloroacetate)

    • 9-Formylphenol (or 9-formyl-compound, 9-aldehyde)

    • Methylene chloride (solvent)

    • Sodium hydroxide solution (50% aqueous)

  • Objective:

    • Combine the starting materials to synthesize a product utilizing a base-catalyzed reaction.

Procedure Steps

## Initial Combination of Materials

  • Step 1: Combine solids in the round-bottom flask.

    • Rinse the flask with methylene chloride to ensure all solid is included.

    • Incorporate the spin vane into the flask.

  • Step 2: Carefully pour the methylene chloride into the flask using a funnel.

    • Any solid stuck within the funnel can be rinsed down with additional methylene chloride.

  • Step 3: Start the stirring process on a stir plate.

    • Ensure the stirring is at a low speed to avoid splashing.

    Addition of Sodium Hydroxide Solution

  • Step 4: Add sodium hydroxide solution dropwise over a period of three minutes (off-camera).

    • The importance of this addition process is to maintain reaction control.

  • Step 5: Allow the mixture to stir at room temperature for 30 minutes.

    • Consistent stirring is crucial to ensure the reaction proceeds adequately.

Separation Process

## Transferring Reaction Mixture

  • Step 6: Remove the flask from the hot plate after 30 minutes of stirring.

    • Extract the magnetic spin vane and observe the reaction mixture, which should have a yellow color.

  • Step 7: Pour the contents into a separatory funnel.

    • Ensure the funnel is properly closed.

  • Step 8: Rinse the reaction flask:

    • Use 5 mL of methylene chloride and swirl to remove remaining product.

    • Follow up with 5 mL of deionized water, also swirling to aid separation.

  • Step 9: Swirl the mixture within the funnel to promote layer separation.

    Extracting Layers

  • Step 10: After separation, identify the layers.

    • The bottom layer is the methylene chloride containing the product, while the top layer is the aqueous layer.

  • Step 11: Drain the bottom methylene chloride layer into a 125 mL Erlenmeyer flask.

  • Step 12: Repeat the extraction of the aqueous layer with 10 mL additional methylene chloride.

    • Ensure the separatory funnel is sealed during the process.

  • Step 13: Allow the layers to separate completely, then drain the methylene chloride layer into the Erlenmeyer flask again.

Drying Product

  • Step 14: Remove the aqueous layer and dispose of it properly.

  • Step 15: Incorporate calcium chloride pellets into the methylene chloride solution.

    • Monitor for any clumping, indicating the presence of water, which necessitates more drying.

  • Step 16: Decant the solution into a round bottom flask.

    • Ensure clarity of product and minimal losses.

Removal of Solvents

## Utilizing Rotovap

  • Step 17: Utilize a rotovap to remove methylene chloride from the product.

    • Set the water bath to approximately 40 degrees Celsius.

    • Attach the product flask securely to prevent accidents.

  • Step 18: Implement vacuum to enhance evaporation of methylene chloride.

    • Monitor the process, ensuring efficient removal of solvents, with regular checks on the system's functionality.

Recrystallization Process

  • Step 19: After methylene chloride removal, notice the color and state of the product (dark yellow solid).

  • Step 20: Recrystallization using a minimal amount of warmed 1-propanol.

    • Gradually add 1-propanol until product dissolves adequately (approximately 20 mL used).

  • Step 21: Transfer the solution to an ice bath for 5-10 minutes.

    • Observe the formation of suspended crystals in the cooling solution.

Filtration of Crystals

  • Step 22: Collect purified product through vacuum filtration using appropriate setups.

    • Wet the filter paper with 1-propanol to prevent premature passage of crystals below.

  • Step 23: Start vacuum filtration and rinse the flask with additional 1-propanol to recover all product.

  • Step 24: Allow the collected product to air dry under vacuum for 5-10 minutes.

    • After drying, place product in a low-temperature oven (approximately 75 degrees Celsius) for additional drying.

Final Yield and Data Collection

  • Step 25: Weigh the dry crystals on a watch glass accurately after accounting for loss.

    • Record the final weight (approx. 343 mg), considering the weight of the watch glass.

  • Step 26: Determine the melting point of the final product, with a recorded melting point of 124°C and a range of 124-128°C.

  • Step 27: Compile data to include observations, calculations on limiting reagents, theoretical yields, and any errors present in the experiment.

Conclusion

  • Key Takeaway:

    • Emphasis on careful handling and systematic execution of chemical processes to improve yield and purity of products.

  • Potential Errors:

    • Considerations on losses during separation and purification stages impacting overall yield accuracy.

  • ACTUAL DETAILS:

Initial weight of benzyltriphenylphosphonium chloride used: 1.022g________

Intial weight of 9-anthraldehyde used: _____.59g_______

Volume of ethyl acetate used to dissolve the starting materials: ____3.5_ml_______

Volume of aqueous sodium hydroxide used: _____1.3 ml_______

Volume of ethyl acetate used to rinse the reaction flask: ___5 ml_________

Volume of water used to rinse the reaction flask: 5 ml__________

Volume of ethyl acetate used to extract the reaction mixture: ____10 ml________

Volume of 1-propanol used to recrystallize crude product extract:___15 ml________

Final weight of purified product:_.612g_____

Melting point range of purified product:__122-125_______

Approximate amount of calcium chloride used to dry the organic extract: 1.6 g________