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

Consult instructor if the vacuum pull appears to be weak04/08/23 9


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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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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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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Di Benz Al Acetone