11 Synthesis Dibenzalacetone

Synthesis of Dibenzalacetone by Aldol CondensationThe aldol condensation is a reaction between two aldehydes or ketones, catalyzed by a base or acid, generating a molecule having both alcohol and aldehyde functional groups. The aldol product is either a β-hydroxyaldehyde or a β-hydroxyketone. This reaction is an important synthetic mechanism that produces large molecules through the formation of carbon-carbon bonds. The product results from the addition of one molecule of an aldehyde or ketone to a second molecule in such a way that the α-carbon of the first molecule becomes attached to the carbonyl carbon of the second molecule. Conjugation of the newly formed double bond with the carbonyl group stabilizes the unsaturated product and provides the thermodynamic driving force for the dehydration process. The overall two-step sequence of reactions involves aldol formation and dehydration. The steps involve an acid-base reaction between a strong base such as the hydroxide ion and a hydrogen located α to a carbonyl group of the aldehyde or ketone. The acidity of the organic species is large relative to most hydrogens that are bonded to carbon due to the resonance stabilization of the enolate that is formed. The enolate attacks the carbonyl group and the aldol undergoes an acid-base reaction with the remaining acidic α-hydrogen, followed by the loss of OH– as a leaving group to give an enol. The net loss of H+ and OH– represents the loss of water, therefore the term aldol condensation. In this experiment, you will run an aldol condensation between benzaldehyde and acetone. The reaction is shown below. The product precipitates out of solution and can be collected by filtration. Melting temperature analysis will be used to characterize the product. O O O 2 H + N a O H (a q ) R' R E tO H + R R' 2 H2O OBJECTIVES In this experiment, you will • • • Perform an aldol condensation between benzaldehyde and acetone. Purify the product by recrystallization. Characterize the product by melting temperature analysis. Organic Chemistry with Vernier © Vernier Software & Technology 1 Tare the weight again and add benzaldehyde dropwise until the mass is 1.01 g. Clamp the round bottom flask to a ring stand and lower the flask onto the stir plate.25 g. Add 5 mL of ethanol to the flask. Add 1. e. c. Protect your arms and hands by wearing a long-sleeve lab coat and gloves. Record the actual mass to the nearest 0.5 M NaOH to the flask.01 g. a.5 mL of 2. d. b. Prepare the reaction mixture. 2 Organic Chemistry with Vernier . Record the actual mass to the nearest 0. Prepare an ice water bath in a 250 mL beaker. Obtain and wear goggles. denatured ice distilled water balance weighing paper watch glass spatula 18×150 mm test tube two 250 mL beakers hot plate ring stand with utility clamp Büchner funnel filtering flask filter paper disposable Pasteur pipets and bulb spatula Part III Melting Temperature glass stirring rod watch glass ethanol. Place the 50 mL round bottom flask containing a stir bar in a clean 250 mL beaker and tare the weight on a balance. denatured ice distilled water balance weighing paper compressed air LabQuest or computer interface LabQuest App or Logger Pro Vernier Melt Station glass capillary tubes.5 M sodium hydroxide solution ethanol. 2. Slowly add acetone dropwise to the flask until the mass is about 0.0 g. one end closed tissues (preferably lint-free) sample from part II mortar and pestle PROCEDURE Part I Synthesis of Dibenzalacetone 1. 3. f. Conduct this reaction in a fume hood.MATERIALS Part I Synthesis of Dibenzalacetone 50 mL round-bottom flask stir bar three 250 mL beakers 10 mL graduated cylinder magnetic stirrer/hot plate ring stand with utility clamp Büchner funnel filtering flask filter paper disposable Pasteur pipets and bulb Temperature Probe or thermometer Part II Recrystallization acetone benzaldehyde 2. warm the reaction mixture in a 50°C hot water bath for 10 minutes. 16. Transfer your crude product to a test tube and add about 5 mL of ethanol. 9. a. Continue stirring until the solid has completely dissolved. cool the solution in an ice water bath to promote crystallization. While waiting. or direct a gentle stream of air above the Büchner funnel for 10–15 minutes to completely dry the solid.Synthesis of Dibenzalacetone by Aldol Condensation 4. 6. Set up a vacuum filtration using a Büchner funnel. Part II Recrystallization 10. use a mortar and pestle to carefully grind the solid to a powder. Organic Chemistry with Vernier 3 . Stir the solution with the glass stirring rod for 5 minutes.01 g. Clamp the flask to prevent it from tipping. Collect the precipitate. The product from the reaction will be a yellow precipitate. Prepare a 60–70°C hot-water bath in the 250 mL beaker. Monitor the temperature with a Temperature Probe or thermometer. Be sure to weigh and record the mass of the filter paper to the nearest 0. add another 0. Keep the vacuum filtration on for an additional 10 minutes to help air dry the solid. a. Weigh the dried solid on the filter paper and record the mass to 0. Stir the reaction for 15 minutes with the flask open to air.01 g before filtering the solid. Filter the precipitate by vacuum filtration.01 g. The solid should be in a powdered form. Use the minimum amount of solvent needed to dissolve your solid.01 g. 15. place the flask in an ice water bath for 10 minutes. Crystals will not form if too much ethanol is used. Rinse the solid with 5–8 drops of ethanol. Collect the product. set up a vacuum filtration using a Büchner funnel. Obtain a small amount of the solid organic compound. After the precipitate forms. 14. Once the solid has completely dissolved. b. b. If very little precipitate forms. 11. 8. Part III Test the Melting Temperature of Dibenzalacetone. Allow to completely air dry. If it is not. 13. Weigh and record the mass of the filter paper to the nearest 0. If the solid does not dissolve. 5. Wash with cold distilled water.5 mL of ethanol. 7. c. 12. Weigh the dried recrystallized product on the filter paper and record the mass to 0. d. g. The red light will turn on indicating active heating. a more accurate determination of the melting temperature can be made. Start data collection. 4 Organic Chemistry with Vernier . stop data collection. Tap the closed end of the capillary tube on the table top to compress the sample into the closed end. The two values marked on your graph describe the estimated melting temperature range of your substance. d. turn the control knob to the Rapid Heat setting. then choose New from the File menu. you will want to observe the melting process and make a rough estimate of the melting temperature of your sample. time graph. Discard the capillary tube and sample as directed by your instructor. When the entire solid has completely melted. d. Start the data-collection program. 18. mark the temperatures on the graph as previously described. turn the control knob to a setting of 180ºC. mark the graph as previously indicated. Now that you have a rough idea of the melting temperature. e. turn the control knob to a temperature setting corresponding to your expected melting temperature. To do this: a. b. click Mark again. b. Connect the Melt Station sensor cable to LabQuest or to a computer interface. Don’t worry if the heating rate is a bit too rapid. A small amount of the solid will be pushed up into the tube. turn the control knob to the Fan/Cooling setting to get ready for the next trial. and if the sample begins to melt. turn the knob to the Rapid Heat setting. Carefully observe your sample. You are now set up to take melting temperature data for up to 20 minutes. 20. click Mark to mark the temperature on your graph (or press the D key on the computer or the OK button on LabQuest). On the Melt Station. 21.17. When you have determined the approximate melting temperature range for the sample. Store the run by tapping the File Cabinet icon in LabQuest. 19. c. If the solid does not melt by the time the temperature gets to 150ºC. turn the control knob to the 220ºC setting. to determine the melting temperature of the sample: a. Carefully observe the temperature vs. Continue observing your sample. Pack a capillary tube 3–4 mm (~1/8 inch) deep with your sample by inserting the open end into a small pile of the solid. Check the control knob on the Melt Station to confirm that it is in the Off position. On the Melt Station. The blue light will turn on indicating that the fan is cooling the Melt Station. as described in Steps 16–17. Carefully insert the capillary tube of solid into one of the sample holders of the Melt Station. 22. Start data collection. c. and the sample melts too quickly. c. When the sample finally begins to melt. If the solid begins to melt. Use a previously prepared sample in a capillary tube. When the temperature is within approximately 10ºC of the lowest possible melting temperature of your sample. In the first trial. On the Melt Station. b. or choosing Store Latest Run from the Experiment menu in Logger Pro. Connect the Melt Station power supply to a powered electrical outlet. Prepare a sample for melting. f. If the sample has not melted by the time the temperature gets to 190ºC. a. click Mark again. DATA TABLE Part I Synthesis of Dibenzalacetone Mass of acetone (g) Mass of benzaldehyde (g) Mass of filter paper (g) Mass of filter paper and product (g) Mass of crude product (g) Part II Recrystallization Mass of filter paper (g) Mass of filter paper and product (g) Mass of recrystallized product (g) Part III Melting Temperature of Dibenzalacetone dibenzalacetone Measured melting temperature range (°C) DATA ANALYSIS 1. turn the control knob on the Melt Station to Off.Synthesis of Dibenzalacetone by Aldol Condensation d. The two values marked on your graph describe the estimated melting temperature range of your substance. When the solid begins to melt. On the Melt Station. What is the theoretical yield of dibenzalacetone in your synthesis? What is the actual yield? Organic Chemistry with Vernier 5 . g. 23. Repeat Step 22 until you have determined the melting temperature range of the solid. Store the run. Carefully observe your sample. Record the range in the data table. When you are finished with this step. click Mark to mark the temperature on your graph. Discard the capillary tube and sample as directed by your instructor. stop data collection. 24. e. At the end of the experiment. f. When the entire solid has completely melted. turn the control knob to the Fan/Cooling setting to get ready for the next trial. Physical hazard−2. Moderately toxic by ingestion. nausea and headache. If too much ethanol is added during the recrystallization step. the solvent can be evaporated by excess heating and directing a gentle stream of air at the test tube will facilitate the process. CAUTION: Heat is released. wear gloves and eye protection when using this substance. HMIS Classification: Health hazard−2. very dangerous to eyes. Addition of denaturant makes the product poisonous. Vapor causes weakness. Physical hazard−0. Flammability−2. Physical hazard−1. Store in dedicated flammables cabinet. Skin and eye irritant.. 2. Flammability−3. much heat evolves when added to water. The reaction is exothermic. Flammability−0. Physical hazard−1. Acetone: Fire hazard (flash point −17. Sodium Hydroxide: Corrosive solid.sigmaaldrich. Dry the product thoroughly before performing a melting temperature analysis. Acetone and ethanol are flammable. 1-800-325-3010.0°C). Prepare cold distilled water by placing distilled water wash bottles in an ice water bath at the start of the lab period.html COMPOUND INFORMATION Compound sodium hydroxide Chemical formula NaOH Melting temperature (°C) 318 Molar mass (g/mol) 40. HMIS Classification: Health hazard−3.INSTRUCTOR INFORMATION 1.0°C).com/safety-center/msds-search. 3. 5. HMIS Classification: Health hazard−3. Flammability−3. Dispose of hazardous waste appropriately. Keep away from open flames. The melting temperature range of the product. HMIS Classification: Health hazard−2. 4. Skin and eye irritant. HAZARD ALERTS Benzaldehyde: Moderately toxic by ingestion. dibenzalacetone.0 6 Organic Chemistry with Vernier . May cause respiratory tract irritation. Skin and eye irritant. www.5 M sodium hydroxide solution by adding 100 g of solid sodium hydroxide to enough distilled water for 1 L of solution. 6. Store in dedicated flammables cabinet. The hazard information reference is: Sigma-Aldrich Co. Ethanol: Fire risk (flash point 14. Prepare the 2. skin burns are possible. Moderately toxic by ingestion and inhalation. is 110–112°C. fatigue. Moderately toxic by inhalation or ingestion. Flammable. 7. 789 (25°C) SAMPLE RESULT Melting temperature graph of dibenzalacetone.07 Density (g/mL) 1.3 Molar mass (g/mol) 106.08 46. Organic Chemistry with Vernier 7 .044 (20°C) 0.12 58.Synthesis of Dibenzalacetone by Aldol Condensation Compound benzaldehyde acetone ethanol Chemical formula C7H6O C3H6O CH4O Boiling temperature range (°C) 178–179 56 78.791 (25°C) 0.