of Synthesis Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Overview Synthesis of Dibenzalacetone Mixed Aldol Condensation (Claisen Schmidt) reaction between Acetone and Benzaldehyde in the presence of 95% Ethanol and 10% Sodium Hydroxide. Determination of Mass, Moles, Molar Ratio, Limiting Reagent, Theoretical Yield. Vacuum Filtration Recrystallization (from Ethanol) Melting Point
References: Slayden Pavia Schornick - p. 77 - p. 61 68 - http://classweb.gmu.edu/jschorni/chem318
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Laboratory Report 1. Synthesis Experiment Mass, Moles, Molar Ratio, Limiting Reagent, Theoretical Yield 1. 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 Dont copy book!! Neat, logically designed template to present of results 2. Summary Paragraph summarizing the experimental results and computed results 3. Analysis & Conclusions
Limiting reagent Discuss reaction mechanism in the context of your experimental results. Verification of product.
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction) The Reaction
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
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 Vacuum Filtration Recrystallization (from Ethanol) Vacuum Filtration Dry Sample Melting Point
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Reagents Benzaldehyde Acetone Ethanol Sodium Hydroxide 2.8 mL (27.6 mmoles or 2.93g)
1.0 mL (13.5 mmoles, i.e. < half the amount of Benzaldehyde 15 mL 95% Ethyl Alcohol 12 mL 10% Aqueous NaOH
Note: Acetone is intended to be the limiting reagent and is to be limited to just less than the Molar equivalent of Benzaldehyde used (see stoichiometric Molar ratio). An excess of Acetone would inhibit the DiSubstitution 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).
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction) Procedure
1. To a 125 mL Erlenmeyer Flask add: 15 mL Ethanol 95% and 12 mL 10% Sodium Hydroxide (NaOH). 2. Obtain a vial of Benzaldehyde from the instructor containing approximately 2.8 mL of Benzaldehyde. 3. Weigh the vial to the nearest 0.001 g. 4. After weighing the vial containing the Benzaldehyde, add the contents to the Erlenmeyer Flask containing the Ethanol & NaOH. Note: Weigh the empty vial. 1. Swirl the mixture. 2. To this mixture add exactly 1.00 ml Acetone from a Volumetric Pipet. 3. Swirl for 5 minutes during which time the solution will change color, followed by the formation of a pale-yellow precipitate. 4. The precipitate will change from a fine grained precipitate to a more coagulated/lumpy form in a minute or so. If it does not, see instructor.
Synthesis of Dibenzalacetone Synthesis of Dbenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Procedure (Cont) 1. As soon as the precipitate thickens, pour the contents into a Buckner funnel and perform a Vacuum Filtration. 2. Wash the crystals with two (2) 25 mL portions of distilled water to remove all traces of the base (NaOH). 3. The waste from this step can be flushed down the drain. 4. Recrystallize the crude product from Ethanol starting with 10 mL Ethanol. Up to two (2) additional increments of 5 ml Ethanol can be added as necessary for a maximum total of 20 ml. 5. Separate the recrystallized product from the Ethanol by Vacuum Filtration, washing the product with two (2) 10 mL portions of Ethanol. 6. Place Vacuum Filtration Waste in the appropriate bottle in hood.
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Procedure (Cont) 1. 2. 3. 4. Place the Crystals from the Vacuum Filtration on a pre-weighed watch-glass. Place the watch-glass and sample in the oven (~ 85oC) (near the door) and allow to dry for about 30 minutes. Determine the Mass of the dried product. Determine melting point of the product. (MP Dibenzalacetone 113oC (decomposes). 5. Compute percent yield.
Synthesis of Dibenzalacetone Mixed Aldo Condensation (Claisen-Schmidt Reaction)
Procedure (Cont) Report Notes: 1. In your report compute the Mass of Benzaldehyde by weighing the vial + Benzaldehyde and the empty vial. 2. Compute the Mass of Acetone from the Volume and Density. Acetone Density 0.7857 g/mL 3. Compute the Moles of Benzaldehyde and Acetone Benzaldehyde: MW 106.12 Acetone: MW 58.08 4. Set up the Stoichiometric Balanced Equation and Determine the Molar Ratio of Benzaldehyde to Acetone. 5. 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 the moles of Benzaldehyde.