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Planning a Reaction

Planning a Reaction. Proposing a Procedure. Library Primary literature SciFinder Scholar Secondary Literature Organic Syntheses Fieser Comprehensive Organic Transformations. Case Study: Benzoic Acid. Literature: Try a Grignard Reaction Well defined purpose Propose a reaction.

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Planning a Reaction

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  1. Planning a Reaction

  2. Proposing a Procedure • Library • Primary literature • SciFinder Scholar • Secondary Literature • Organic Syntheses • Fieser • Comprehensive Organic Transformations

  3. Case Study: Benzoic Acid • Literature: Try a Grignard Reaction • Well defined purpose • Propose a reaction Done with the hard part—Right????

  4. Considerations • More left to consider than you think! • Scale of reaction • Solvent/amount of solvent • Glassware • Size • Inert atmosphere? • Order of reagents and addition • Temperature and reaction time • Isolation/purification of product

  5. Scale of Reaction • Macroscale: multigram • Miniscale: 0.5g-10g • Microscale: <0.5g • Consider • Purpose • Further steps • Practicalities • Projected yield • Apply to our Grignard reaction

  6. Solvent • What solvent? • Solubility, protic/aprotic • How much solvent? • Scale down: use proportionally more solvent • Scale up: use proportionally less solvent • Rule of thumb: 0.1M-0.5M • Example: You are basing your reaction on a procedure that has 5 mmol of bromobenzene in 10 mL of ether solvent. If you are scaling down to 0.5 mmolstarting material, how much ether should you use?

  7. Special Considerations for Grignard • Reaction mechanism: Radical chain • Wet glass/ether stops initiation • Too dilute, and the reaction doesn’t initiate • Too concentrated, and the reaction stops • Pay attention to amounts of solvent and order of addition

  8. Glassware • Size? • 1/2to 1/3 full • Heating/cooling? • Anhydrous? • Adding reagents?

  9. Which reagent first? How do we add gradually? Does it matter if we switch the addition funnel and reflux condenser?

  10. Heating: Waterbath? Sandbath? Hotplate? Cooling: Icebath? How long?

  11. Questions for Discussion • Reaction times are given for you. How would you determine reaction times if not given? • At the end of the hydrolysis, you will have your product mixed with_____. (Also consider the byproduct, biphenyl.) Propose a workup. Propose a purification.

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