1. Synthesis of Dibenzalacetone
Synthesis of Dibenzalacetone via Mixed Aldol Condensation (Claisen – Schmidt) reaction between Acetone and Benzaldehyde in the presence of 95% Ethanol and 20% Sodium Hydroxide
References:
Slayden - p. 77
Pavia - p. 61 – 68
Schornick -
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2. Synthesis of Dibenzalacetone
Overview
Synthesis of Dibenzalacetone via mixed Aldol Condensation (Claisen – Schmidt) reaction between Acetone and Benzaldehyde in the presence of 95% Ethanol and 20% Sodium Hydroxide
Determination of Mass, Moles, Molar Ratio, Limiting Reagent, Theoretical Yield
Vacuum Filtration
Recrystallization (from Ethanol)
Melting Point
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3. Synthesis of Dibenzalacetone
Laboratory Report
Synthesis Experiment
Mass, Moles, Molar Ratio, Limiting Reagent, Theoretical Yield
Procedures:
Title – Be Concise Ex. Vacuum Filtration, Recrystallization, etc.
Materials & Equipment – 2 Columns in list (bullet) form Note: include all reagents and principal equipment
Description of Procedure:
Use list (bullet) form
Concise, but complete descriptions
Use your own words – Don’t copy book!!
Neat, logically designed template to present of results
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4. Synthesis of Dibenzalacetone
Summary
Paragraph summarizing the experimental results and computed results
Analysis & Conclusions
Limiting reagent
Discuss reaction mechanism in the context of your experimental results
Verification of product
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5. Synthesis of Dibenzalacetone
The Reaction
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6. Synthesis of Dibenzalacetone
Elements of the Experiment:
Determination of Mass of Reagents
Compute Moles
Determine Molar Ratio (Acetone:Benzaldehyde), Limiting Reagent and Theoretical Yield
Note: The Molar Ratio is not 1:1
Mix Reagents & Initiate the Reaction by swirling
1st Vacuum Filtration
Recrystallization (from Ethanol)
2nd Vacuum Filtration
Dry Sample
Melting Point
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7. Synthesis of Dibenzalacetone
Reagents
Benzaldehyde 2.8 mL (27.6 mmoles or 2.93g)
Acetone 1.0 mL (13.5 mmoles, (~ half the the amount of Benzaldehyde)
Ethanol 20 mL 95% Ethyl Alcohol
Sodium Hydroxide 5 mL 3 M (10%) NaOH
Note: Amounts of Benzaldehyde and Acetone reagents supplied will be close to the reaction molar ratio.
Thus, the computed molar ratio could result in either one being selected as the “limiting” reagent.
Select the limiting reagent based on your calculations
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8. Synthesis of Dibenzalacetone
Procedure
To a clean, dry 125 mL Erlenmeyer Flask add:
15 mL 95% Ethanol and
5 mL 3 M Sodium Hydroxide (NaOH)
Obtain a vial of Benzaldehyde from the instructor containing approximately 2.8 mL of Benzaldehyde
Weigh the vial to the nearest g
To the vial containing the Benzaldehyde, add 1.0 ml Acetone
Weigh the vial again
Add ½ the contents of the vial (Benzaldehyde and Acetone), with swirling, to the Erlenmeyer flask containing the Ethanol & NaOH
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9. Synthesis of Dibenzalacetone
Swirl for 15 minutes
Add the remaining Benzaldehyde/Acetone solution to the basic mixture and rinse the containiner with 2 or 3 ml of 95% Ethanol to complete the tranfer.
Swirl the mixture for an additional 15 minutes
Weigh the empty vial
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10. Synthesis of Dibenzalacetone
Procedure (Con’t)
Buckner Funnel and tubing
Vacuum filtration
Set up Filter flask with Buckner funnel
Place a paper filter into the Buckner funnel
Moisten the filter paper with Distilled Water
Pour the contents of the Erlenmeyer flask into the Buckner funnel and perform a Vacuum Filtration
Continue filtration until all liquid passes into flask
Wash the crystals with two (2) 25 mL portions of Distilled Water to remove all traces of the base (NaOH)
Note: The waste from this step can be flushed down the drain
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11. Synthesis of Dibenzalacetone
Recrystallization
Transfer the product to a 150 mL Beaker rinsing the funnel with 10 ml Ethanol
Heat mixture until solids dissolve completely
Note: It may be necessary to add one or more 1 mL Ethanol increments to effect complete dissolution
Remove the beaker from the hot plate and allow to cool slowly to room temperature
Vacuum filtration # 2
Transfer the mixture to a clean Buckner with a new paper filter
Continue filtration until all liquid passes into the flask
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12. Synthesis of Dibenzalacetone
Procedure (Con’t)
Vacuum Filtration #2 (con’t)
Wash the product with two (2) 10 mL portions of Ethanol
Note: Vacuum process must be complete for each step
Place Vacuum Filtration Waste into the appropriate bottle in hood
Place the Crystals from the Vacuum Filtration on a pre-weighed weighing tray
Place the weighing tray in the class drawer and allow to dry for a week
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13. Synthesis of Dibenzalacetone
Procedure (Con’t)
Determine the Mass of the dried product
Compute percent yield
Determine melting point of the product (MP Dibenzalacetone – 113oC (decomposes)
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14. Synthesis of Dibenzalacetone
Report Notes:
Acetone is intended to be the limiting reagent. Since the molar ratio of Acetone to Benzaldehyde is 1:2, the moles of Acetone should be less than ½ the moles of Benzaldehyde
An excess of Acetone would inhibit the Di-Substitution from taking place
Since the Aldehyde Carbonyl group is more reactive than the Acetone carbonyl and only the Acetone can form an enolate ion, only one condensation reaction is likely to occur
The Sodium Hydroxide base promotes dehydration (removal of the two water molecules)
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15. Synthesis of Dibenzalacetone
Report Notes:
Calculations (in your report)
Determine the mass of Benzaldehyde:
(Mass of Vial + Benzaldehyde) - (Mass of Empty Vial)
Determine the mass of Acetone:
Mass (Vial + Benzaldehyde + Acetone) – Mass (Vial + Benzaldehyde)
Compute of moles of Benzaldehyde and Acetone
Benzaldehyde: Mol Wgt –
Acetone: Mol Wgt – Density – g/cm3
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16. Synthesis of Dibenzalacetone
Report Notes
Calculations (con’t)
Compute the actual molar ratio of Acetone to Benzaldehyde
Compare actual mole ratio to Stoichiometric mole ratio
Determine Limiting Reagent based on the actual moles of Benzaldehyde and Acetone used and the Stoichiometric Molar Ratio
Note: The actual Moles of Acetone should be equal to or just less than ½ the moles of Benzaldehyde
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