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Organic Chemistry Lab 318

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Title: DUE DATES Author: SWS Last modified by: user Created Date: 9/19/2005 12:47:50 AM Document presentation format: On-screen Show (4:3) Company – PowerPoint PPT presentation

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Title: Organic Chemistry Lab 318


1
  • Organic Chemistry Lab 318
  • Spring, 2012

2
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

3
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

4
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

5
Synthesis of Dibenzalacetone
  • The tetrahedral intermediate from addition is
    protonated
  • Then dehydration occurs to give a stable
    conjugated product (a,b-unsaturated ketone)

6
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).

7
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

8
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.

9
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).

10
Experiment Notes
  • Empty your vial containing the aldehyde/ketone
    unknown into the Waste container in the hood.
  • Wash the vial.
  • Clean-up Tiffany Nguyen
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