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Expt. 17.1A Microscale Wittig Synthesis of trans-9-2-phenylethenylanthracene

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Expt. 17.1A Microscale Wittig Synthesis of trans-9-2-phenylethenylanthracene

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    1. Expt. 17.1A Microscale Wittig Synthesis of trans-9-(2-phenylethenyl)anthracene

    2. Georg Wittig: The Wittig Reaction

    3. Convert an aldehyde (9-anthraldehyde) into an alkene (trans-9-(2-phenylethenyl)anthracene) using the Wittig reaction Recrystallize the crude product Identify the product using melting point and TLC Purpose

    4. Generic Wittig Reaction

    5. Phosphorus Ylides Prepared from triphenylphosphine and an unhindered alkyl halide. (What kind of reaction is this?) phosphonium salt A strong base then abstracts a hydrogen from the carbon attached to phosphorus.

    6. The negative carbon on ylide attacks the partial positive carbon of the carbonyl to form an oxaphosphetane. Oxygen combines with phosphine to form the triphenylphosphine oxide and the alkene. Wittig Mechanism

    7. Wittig Summary Make the phosphonium salt triphenylphosphine + alkyl halide Form the ylide Phosphonium salt + strong base Generate the alkene Ylide + aldehyde or ketone Usually get both E and Z isomers

    8. Overall Lab Reaction

    9. Formation of Our Ylide

    10. Pre-lab Preparation Read Background and Expt. 17.1A. Read Carey, parts of Ch 17 pertaining to Wittig Review Technique K, TLC Prepare Notebook (as usual) Follow the guidelines in the syllabus example for a preparative lab. Items for table: Starting materials, product, solvents (do not need to list water).

    11. Spot 9-anthraldehyde (provided) triphenylphosphine oxide (provided) trans-9-(2-phenylethenyl)-anthracene (provided) crude product recrystallized product Develop in CH2Cl2 10 mL in a 400 mL beaker TLC

    12. After Lab Allow product to dry for at least 24 hours. Then get the weight and MP Notebook Calculations theoretical and % yield MP % error Calculate Rf values (five) Notebook Results and Conclusion Determine identity and stereochemistry of product based upon TLC and melting point. Comment on the purity of your product Draw your product showing stereochemistry

    14. Color and Structure

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