Organic Chemistry Lab 318

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• Organic Chemistry Lab 318
• Spring, 2012

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DUE DATES

• Today
• Banana Oil Report at beginning of lab
• Quiz notebook copy of todays experiment
• At end of lab -- copy of the remainder of the
  laboratory notebook pages for today's experiment
• Next Week
• -Dibenzalacetone Report at beginning of lab

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Synthesis of Dibenzalacetone

• This reaction is an example of an aldol
  condensation
• The reaction is also a mixed aldol, between and
  aldehyde and a ketone
• The product is quite stable because of
  conjugation (resonance stabilization), and so
  product formation is highly favored

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Synthesis of Dibenzalacetone

• Only the ketone has an alpha-H that can be
  removed by OH- base to form the enolate
• The carbonyl group in the aldehyde is more
  reactive than the carbonyl of the ketone

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Synthesis of Dibenzalacetone

• The tetrahedral intermediate from addition is
  protonated
• Then dehydration occurs to give a stable
  conjugated product (a,b-unsaturated ketone)

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Synthesis of Dibenzalacetone

• The reaction is repeated by removing the a-H from
  the ketone and the enolate reaction with the
  aldehyde, followed by dehydration
• The product has two trans double bonds (more
  stable).

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The Experiment

• The experiment is very simple follow the
  instructions on p. 103 of the Manual.
• You will need to calculate the quantity of
  acetone to use based on the amount of
  benzaldehyde that is in your vial.
• Weigh the vial contents pour contents into
  smallest Erlenmeyer flask weigh empty vial.
• Add the calculated volume of acetone to the flask

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The Experiment

• Use another smallest Erlenmeyer flask to prepare
  a mixture of 95 ethanol and 10 NaOH
• Add half of the PhCHO/acetone mixture to the
  ethanol/base mixture
• Swirl for 15 min.
• Add the remainder of the PhCHO/acetone mixture to
  the reaction flask, and swirl for 15 min.

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The Experiment

• Isolate the crude product by vacuum filtration
  and wash with 3 portions of distilled water (the
  dibenzalacetone is very insoluble in water).
• Recrystallize the crude product from 95 ethanol
  using about 10 ml of ethanol for every 4 g of
  crude product.
• Use cold ethanol to wash the filtered product.
• Put product in pre-weighed vial. Weigh vial
  product (wet product no m.pt. this week).

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Experiment Notes

• Empty your vial containing the aldehyde/ketone
  unknown into the Waste container in the hood.
• Wash the vial.
• Clean-up Tiffany Nguyen