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 - http://classweb.gmu.edu/jschorni/chem318
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Synthesis of Dibenzalacetone
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Overview
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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)

Vacuum Filtration

Melting Point
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Synthesis of Dibenzalacetone
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Laboratory Report
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Synthesis Experiment
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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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Synthesis of Dibenzalacetone
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Summary

Paragraph summarizing the experimental results
and computed results
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Analysis & Conclusions

Limiting reagent

Discuss reaction mechanism in the context of
your experimental results

Verification of product
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Synthesis of Dibenzalacetone
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The Reaction
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Synthesis of Dibenzalacetone
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Elements of the Experiment:
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Determination of Mass of Reagents

Compute Moles
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Determine Molar Ratio (Acetone:Benzaldehyde),
Limiting Reagent and Theoretical Yield
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Note: The Molar Ratio is not 1:1
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Mix Reagents & Initiate the Reaction by swirling
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1st Vacuum Filtration
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Recrystallization (from Ethanol)
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2nd Vacuum Filtration
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Dry Sample

Melting Point
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Synthesis of Dibenzalacetone
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Reagents
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Benzaldehyde
2.8 mL (27.6 mmoles or 2.93g)
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Acetone
1.0 mL (13.5 mmoles, (~ half the
the amount of Benzaldehyde)

Ethanol
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Sodium Hydroxide
20 mL 95% Ethyl Alcohol
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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Synthesis of Dibenzalacetone
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Procedure
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To a clean, dry 125 mL Erlenmeyer Flask add:
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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
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Weigh the vial to the nearest 0.001 g
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To the vial containing the Benzaldehyde, add 1.0 ml
Acetone

Weigh the vial again
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Add ½ the contents of the vial (Benzaldehyde and
Acetone), with swirling, to the Erlenmeyer flask
containing the Ethanol & NaOH
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Synthesis of Dibenzalacetone
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Swirl for 15 minutes
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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.
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Swirl the mixture for an additional 15 minutes
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Weigh the empty vial
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Synthesis of Dibenzalacetone
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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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Synthesis of Dibenzalacetone
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Recrystallization
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Transfer the product to a 150 mL Beaker rinsing the
funnel with 10 ml Ethanol
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Heat mixture until solids dissolve completely
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Note: It may be necessary to add one or more
1 mL Ethanol increments to effect complete
dissolution
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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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Synthesis of Dibenzalacetone
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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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Synthesis of Dibenzalacetone
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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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Synthesis of Dibenzalacetone
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Report Notes:
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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
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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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Synthesis of Dibenzalacetone
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Report Notes:
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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 – 106.12
Acetone:
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Mol Wgt – 58.08
Density – 0.791 g/cm3
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Synthesis of Dibenzalacetone
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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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