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

04/20/23 1

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) Vacuum Filtration Melting Point

04/20/23 2

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

04/20/23 3

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

04/20/23 4

Synthesis of Dibenzalacetone The Reaction

04/20/23 5

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

04/20/23 6

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

04/20/23 7

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 0.001 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

04/20/23 8

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

04/20/23 9

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

04/20/23 10

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

more1 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 flask04/20/23 11

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

04/20/23 12

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)

04/20/23 13

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)

04/20/23 14

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 – 106.12

Acetone: Mol Wgt – 58.08 Density – 0.791 g/cm3

04/20/23 15

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

04/20/23 16