Experiment #9- CHEM 2212

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University Of Georgia *

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2212

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Chemistry

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Feb 20, 2024

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I. Introduction The aldol condensation is a base catalyzed coupling reaction. It couples two carbonyl compounds, usually ketones or aldehydes. The reaction can occur between two of the same carbonyl compounds or two different carbonyl compounds. A catalytic amount of base is sued in the reaction to abstract an alpha carbanion. The carbanion is stabilized via resonance with the adjacent carbonyl. This creates an enolate intermediate. The second step of this reaction involves the enolate species reacting with a second equivalent of the material reacting with the propanol starting material. The alpha carbanion undergoes nucleophilic addition the electrophilic carbonyl of the aldehyde. The reaction is neutralized with water in order to protonate the alkoxide intermediate forming a beta hydroxy aldehyde. The final compound has both an alcohol and carbonyl group. In this experiment particularly only one carbonyl has alpha hydrogens and so acetone will be the only nucleophile for this reaction. The final product obtained will be the dehydrated product due to the stability of the conjugated system. II. Balanced Equation III. Reaction Mechanism H O H OH H O H O H O + O H O O H OH H O OH H OH H O IV. Table of Reagents

Reagent Structure Molecul ar weight Boiling point or meltin g point Densi ty Acetone O Acetone 58.08 g/mol BP: 56 0.791 g/mL p-Tolualdehyde O p-Tolualdehyde 120.15 g/mol BP:205 1.019 g/mL o-Tolualdehyde O o-Tolualdehyde 120.15 g.mol BP:200 1.039 g/mL 4- Methoxybenzalde hyde O O 4-Methoxybenzaldehyde 136.15 g/mol BP:248 1.12 g/mL Benzaldehyde O Benzaldehyde 106.12 g/mol BP: 178.1 1.04 g/mL Ethanol OH Ethanol 46.068 g/mol BP:78. 37 0.79 g/mL Sodium hydroxide Na + OH - Sodium hydroxide 39.997 g/mol MP: 318 (1E,4E)-1,5- diphenylpenta-1,4- dien-3-one O (1E,4E)-1,5-diphenylpenta-1,4-dien-3-one 294.4 g/mol MP: 110-11 (1E,4E)-1,5-di-o- tolylpenta-1,4- dien-3-one O (1E,4E)-1,5-di-o-tolylpenta-1,4-dien-3-one 262.3 g/mol MP; 98-100 (1E,4E)-1,5-di-p- tolylpenta-1,4- dien-3-one O (1E,4E)-1,5-di-p-tolylpenta-1,4-dien-3-one 262.3 g/mol MP:17 4-177

(1E,4E)-1,5-bis(4- methoxyphenyl)pe nta-1,4-dien-3-one O O O (1E,4E)-1,5-bis(4-methoxyphenyl)penta-1,4-dien 294.3 g/mol MP:12 8-132 V. Safety Information a. General Safety information i. Wear safety goggle, gloves and lab coat. ii. Ensure snorkel is working properly iii. Handle hot glassware carefully. b. Specific safety information Acetone- flammable, causes serious eye damage, can cause dizziness p-tolualdehyde- flammable, harmful if swallowed, can cause serious eye and skin irritation, may cause respiratory issues o-tolualdheyde- flammable, harmful if swallowed, can cause serious eye and skin irritation, may cause respiratory issues 4-Methoxybenzaldehyde- short and long term aquatic hazard Benzaldehyde- flammable, toxic if inhaled or ingested, can cause eye and skin irritation, toxic to respiratory system, harmful to aquatic life Ethanol- flammable, dp not inhale Sodium hydroxide- serious eye damage, corrosive to metals and skin (1E,4E)-1,5-diphenylpenta- 1,4-dien-3-one- harmful if swallowed, harmful to aquatic life (1E,4E)-1,4-di-o-tolylpenta-1,4-dien-3-one- harmful if swallowed, harmful to aquatic life (1E,4E)-1,5-di-p-tolylpenta-1,4-dien-3-one- harmful if swallowed, harmful to aquatic life (1E,4E)-1,5-bis(4-methoxyphenyl)penta- 1,4-dien-3-one- irritant VI. Experimental Procedure 1. Use 3 mL conical vial. Add 1.0 mL of ethanol, use 0.65 mL of aldehyde, and 0.20 mL of acetone. 2. Add three drops of sodium hydroxide to vial. 3. Cap and shake vial vigorously for several minutes. 4. Let reaction react at room temp for 15 min. 5. Shake vial at regular short intervals to ensure mixing. 6. Chill reaction mixture in ice bath after 15 min. 7. Use a mL of DI water to rinse reaction vessel. 8. Use suction filtration to separate crystals. 9. Use a mL of water and pour on top of crystals. 10. Repeat 3 more times. 11. Test pH of water coming out of funnel. Should be orangeish 12. Dry crystals with suction filtration for a couple of minutes. 13. Scrape crystals into 100 mL beaker.

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14. Use warm ethanol to recrystallize the product. 15. Let cool on bench top and then put into ice bath. 16. Use suction filtration to isolate crystals. 17. Rinse flask with water. 18. Scrape product onto watch glass and dry product. 19. Weigh final product. 20. Find melting point value and identify unknown. In-Lab: VII. Data and Observations a. Unknown code: AC489918 b. Initial volume and weight of the aldehyde used: 0.65 mL c. Initial volume and weight of the acetone: 0.2 mL d. Volume of ethanolic sodium hydroxide solution used to catalyze: 3.0 mL e. Total reaction time: 30 min f. Volume of water used to rinse the crude product: 3.0 mL g. Volume of water used to neutralize the rection: 15.0 mL h. Volume of ethanol used to recrystallize: 10.0 mL i. Final weight: 0.002 g j. Once all starting materials were added to the reaction flask the solution turned a canary yellow. While shaking the vessel the liquid got darker and turned slightly orange. It took a very long time for solid to form in the vial and a low weight was recovered. The final product was a banana yellow solid. VIII. Results a. Limiting reagent calculation i. 95% ethanol 3.0 ml x (0.790g/ 1 ml) x (1 mol/ 46.07 g) x (1 mol product/ 1 mol ethanol) = 0.0514 mol ii. Aldehyde (limiting reagent) 0.65 mL x (1.019 g/1 mL) x (1 mol/ 120.15g) x (1 mol product/ 2 mol aldehyde) = 0.00276 mol iii. Acetone 0.2 mL x (0.791 g/ 1 mL) x (1 mol/ 58.08g) x (1 mol product/ 1 mol) = 0.00278 mol b. Percent yield calculation i. Theoretical yield: 0.723 g ii. Percent yield: (0.002/0.723) x 100 = 0.28%

c. Acetone IR Spectra The signal at 3004 cm-1 indicates the presence of sp3 carbons. The strong signal at 1710 cm-1 shows the presence of a carbonyl group. d. Final product Spectra The signal at 3100 cm-1 shows sp2 carbons while the signal at 2900 cm-1 indicates sp3 carbons. The signals at 3000 cm-1, 1590 cm-1, and 1450 cm-1 indicate the presence of a benzene ring.

The signal at 1650 cm-1 indicates a carbonyl group. e. Unknown Aldehyde: o-Tolualdehyde f. Final product: (1E,4E)-1,5-di-o-tolylpenta-1,4-dien-3-one Post-Lab: IX. Results This experiment resulted in a very low percent yield od 0.28%. This percent yield is likely due to not allowing the reaction to react long enough and thus go to completion. When filtering the crude product some of the final product was not solidified and therefore was lost in the waste beaker. The unknown aldehyde was found to be o-tolualdehyde and the final product was (1E,4E)-1,5-di-o-tolylpenta-1,4-dien-3-one. This was determined by analyzing the melting point range. Its melting point range is 98-100 degrees Celsius. The IR spectra’s both indicated the presence of a carbonyl which is to be expected. The acetone IR spectra did not have overtone signals meaning there was no benzene ring. X. Post-Lab Questions 1. p-chlorobenzaldehyde is incapable of undergoing an aldol reaction with itself, explain why. Be specific in your answer: p-chlorobenzaldehyde has o alpha hydrogens and therefore cannot undergo an aldol reaction with itself. At least one compound must have an alpha hydrogen for the base to remove to create the enol-keto tautomer that can lead to the elimination product. 2. Which of your reagents was present in excess? What was the exact molar ratio of your starting materials? Why was this particular ratio necessary? Draw the skeletal structure of the most likely aldol product formed when your specific starting materials are present in a 1:1 molar ratio: The reagent that was in excess was the aldehyde. There needed to be 2 mols of the aldehyde so it would react with the acetone twice, once with each side of the carbonyl. The final product if no excess aldehyde was used: O 3. Students were instructed to mix the benzaldehyde and acetone starting materials in their conical vials before adding the ethanolic sodium hydroxide solution. Why was this essential to the success of the reaction? What would have been the most likely product formed if the sodium hydroxide solution were added to the vial first, followed by acetone and then waiting a few minutes to add the benzaldehyde? Provide a balanced equation showing this reaction: The benzaldehyde and the acetone needed to react first because an acid/base reaction would have taken place between the sodium hydroxide and the acetone.

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4. Provide skeletal structures of the aldol products that form when the following compounds or mixtures of compounds are reacted under basic (NaOH) conditions: O + O O + O NaOH + O H2O + O Na O