Di Benz Al Acetone
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Transcript of Di Benz Al Acetone
Synthesis of Dibenzalacetone
Synthesis of Dibenzalacetone – 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 Overview
Synthesis of Dibenzalacetone – 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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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) formNote: 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 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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Synthesis of Dibenzalacetone The Reaction
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Mol Wgt – 234.29 g/mol
Synthesis of Dibenzalacetone Elements of the Experiment:
Determination of Mass of Reagents (two methods)
Compute Moles Determine Molar Ratio, 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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Synthesis of Dibenzalacetone Reagents
Benzaldehyde 2.8 mL (27.6 mmoles or 2.93g)
Acetone 1.0 mL (13.5 mmoles, i.e. < half the amount of
Benzaldehyde)
Ethanol 15 mL 95% Ethyl Alcohol
Sodium Hydroxide 20 mL 3 M Aqueous NaOH
Note: Acetone is intended to be the limiting reagent and is to be limited to just less than ½ the Molar equivalent of Benzaldehyde used (see stoichiometric Molar ratio). 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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Synthesis of Dibenzalacetone Procedure
To a clean, dry 125 mL Erlenmeyer Flask add: 15 mL 95% Ethanol and 20 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 0.001 g To the vial containing the Benzaldehyde, add
exactly 1.00 ml Acetone from a Volumetric Pipet Weigh the vial again Use the volume & density of Acetone to
determine its mass Determine the mass of Benzaldehyde by
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Synthesis of Dibenzalacetone Procedure (Con’t)
Add the contents of the vial (Benzaldehyde and Acetone) in 2 portions, with swirling, to the Erlenmeyer Flask containing the Ethanol & NaOH
Swirl the mixture until a precipitation occurs, and continue the swirling until the precipitate shows signs of thickening
This can take several minutes Set up the Vacuum Filtration apparatus Moisten the filter paper disk with Distilled Water Pour the contents of the Erlenmeyer flask into the
Buckner funnel and perform a Vacuum Filtration
Note: the filtration process must continue until the precipitate in the Buckner funnel is quite dry
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Synthesis of Dibenzalacetone Procedure (Con’t)
Wash the crystals with two (2) 25 mL portions of Distilled Water to remove all traces of the base (NaOH)
Note: The vacuum process must be complete before adding the second portion of Distilled Water
The waste from this step can be flushed down the drain
Recrystallize the crude product from 10 mL Ethanol
Separate the recrystallized product from the Ethanol by Vacuum Filtration
Wash the product with two (2) 10 mL portions of Ethanol
Note: Vacuum process must be complete for each step
Place Vacuum Filtration Waste in the appropriate bottle in hood
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Synthesis of Dibenzalacetone Procedure (Con’t)
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
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 Procedure (Con’t)
Report Notes: In your report compute the Mass of Benzaldehyde by
weighing the vial + Benzaldehyde and the empty vial Compute the Mass of Acetone from the Volume and Density
Acetone Density – 0.7857 g/mL Compute the Moles of Benzaldehyde and Acetone
Benzaldehyde: MW – 106.12
Acetone: MW – 58.08 Set up the Stoichiometric Balanced Equation and
Determine the Molar Ratio of Benzaldehyde to Acetone. Determine the “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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