Synthesis of Dibenzalacetone

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 - http://classweb.gmu.edu/jschorni/chem318

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) • Vacuum Filtration • Melting Point

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) 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

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

5. Synthesis of Dibenzalacetone • The Reaction

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

7. Synthesis of Dibenzalacetone • Reagents • Benzaldehyde 2.8 mL (27.6mmoles or 2.93g) • Acetone 1.0 mL (13.5 mmoles, (~ half the the amount of Benzaldehyde) • Ethanol 15 mL 95% Ethyl Alcohol • Sodium Hydroxide 20 mL 3 M Aqueous 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

8. 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 1.0 ml Acetone • Weigh the vial again • Add the contents of the vial (Benzaldehyde and Acetone) in 2 portions, with swirling, to the Erlenmeyer flask containing the Ethanol & NaOH

9. Synthesis of Dibenzalacetone • Procedure (Con’t) • Continue to swirl the flask until the precipitate that forms shows signs of flocculation (bigger particles) • Vacuum filtration • Set up Filter flask, Buckner Funnel and tubing • 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

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 flask

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

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)

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)

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

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