experiment 43

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CHEM 324 Organic Chemistry III Experiment 43 Effect of Reaction Conditions on the Condensation of Furfural with Cyclopentanone Jiani He 26380107 Performed on Thursday, October 4 th , 2023 and Thursday, October 19 th , 2023 Submitted on Thursday, October 26 th , 2023

Introduction Experiment 43 consisted of reacting cyclopentanone and furfural, also known as furfuraldehyde, under different conditions in order to obtain different products. Product A , a low-melting yellow solid, is extracted with diethyl ether after having formed under equimolar conditions, dissolved in diethyl ether and stirred vigorously in a sodium hydroxide aqueous solution. Thereafter extraction, the impure mixture is evaporated, distilled under vacuum and crystallized. Product B , a golden-orange crystal, is formed under excess furfural conditions in the presence of tricaprylmethylammonium chloride phase- transfer catalyst. Because this reaction is highly exothermic, the reaction mixture must be on ice during the reaction. Product B is vacuum filtrated and, as per the Teaching Assistant’s discretion, recrystallized with 2-butanone if necessary. The reaction between cyclopentanone and furfural proceeds via a Claisen-Schmidt condensation, which is between two different carbonyl species only gives desired product in high yield under specific conditions, for example, it requires one of the carbonyl compounds to be non-enolizable, and hence act as an electrophile 1 . The general scheme of the reaction is shown below. Figure 1. Claisen- Schmidt condensation for part A Also, the condensation varies depending on reaction parameter such as stoichiometry, temperature, and duration. In this case of CS condensation, if the nucleophilic carbonyl compound has two enolizable side, condensation will occur more than once, as such obtained different products. The scheme of reaction as shown below. Figure 2. condensation for part B.

In this experiment, the CS condensation is performed between the aromatic aldehyde (furfural) and an aliphatic ketone (cyclopentanone) under different conditions in order to produce an α, β- unsaturated carbonyl (Lab Manual, 2023). In the first scenario, where equimolar amounts of cyclopentanone and furfural are used, the reaction proceeds until 2-(2-furylmethylidene) cyclopentanone, or Product A , is formed. When excess furfural is present it entices the deprotonation of 2-(2-furylmethylidene) cyclopentanone which then proceeds to attack furfural and yield product B , or 2, 5-bis (2-furylmethylidene) cyclopentanone. Vacuum filtration, recrystallization and column chromatography were techniques employed in this experiment. While the first was used to isolate and dry the crude product, the latter two were used to purify the product. Recrystallization takes advantages of the difference in solubilities between the target product and impurities at different temperatures. While the compound to be purified dissolves well in the hot solvent and precipitates out as the solution cools, impurities remain dissolved regardless of the temperature, allowing for purification and isolation. Column chromatography involves eluting, with a suitable solvent, the crude product through a column packed with an appropriate stationary phase. Species present in solution interact differently with the stationary phase, this is exploited to separate the desired compound from the impurities. Characterization was accomplished by H NMR. Hydrogen atoms in different chemical environment response differently in the presence of an external magnetic field, leading to signals of different chemical shift, integration and multiplicity that can be used to obtain structural information regarding the product. The goal of the experiment is to explore the effects of conditions on the reaction outcome using the Claisen-Schmidt condensation as a platform. Experimental Data and Observations To a 125 mL Erlenmeyer flask with a magnetic stir bar, cyclopentanone (4.5 mL, 50 mmol) was dissolved in diethyl ether (25 mL). 0.10 M aqueous sodium hydroxide (45 mL, 4.5 mmol) was added. After cooling the mixture to 5 ℃ with an ice bath, freshly distilled furfural (4.2 mL, 50 mmol) was added while stirring. The flask was sealed with parafilm and the solution was vigorously stirred for 45 minutes at 5 ℃ . Diethyl ether was occasionally replenished. The solid was separated with vacuum filtration and washed with diethyl ether (2×10 mL). The solid was discarded and the filtrate was added to a separatory funnel for separation. The aqueous layer was extracted with diethyl ether (1 ×

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15 mL). The ether solution was washed with saturated sodium chloride (1×30 mL) before being dried over anhydrous sodium sulfate. The ether was left evaporated over a week before column chromatography with DCM: hexane : EtOAc (4:4:2) and silica gel was performed for the purification of the product. Rotary evaporation was employed to remove the solvent. The product was not weighed, and its H NMR spectrum was recorded in deuterated chloroform. To a 125 mL Erlenmeyer flask with a magnetic stir bar, cyclopentanone (0.90 mL, 10 mmol) was dissolved in diethyl ether (10 mL). 0.10 M aqueous sodium hydroxide (12.0 mL, 1.2 mmol) and aliquat 336 (6 drops) were added. After cooling to 5 ℃ with an ice bath, freshly distilled furfural (2.0 mL, 24 mmol) was added under vigorous stirring. The ice bath was then removed and the reaction was performed for 15 minutes under strong stirring followed by 10 minutes of less vigorous stirring. The precipitate was separated with vacuum filtration and washed with diethyl ether (2×10 mL). The crude mass was recorded before 1 g of the solid was recrystallized using butanone. The purified and dried product was weighed, and its H NMR spectrum was recorded. No melting point test was performed. For part A, neither vacuum distillation nor mixed-solvent recrystallization was performed. Product A Product B Clear yellow liquid. Upon addition of furfural, the yellow became opaque. Precipitation was observed after 20mins After the week in which the solution mixture evaporated, it was viscous in consistency and reddish in color. In the column, there was the yellow band (the product) and an orange band higher up which contained other molecules from the reaction mixture. At first, the reaction mixture was oily black and creamy-yellow. As it was mixed, it turned brown/yellow with a solid yellow precipitate in it. Final mass: N/A Final Mass: 1.903 g Mechanism: To begin, the hydroxide ion in solution from sodium hydroxide deprotonates one of the alpha hydrogens from the cyclopentanone. This yields an enolate resonance stabilized ion. This enolate then proceeds to attacking the carbonyl of the furfural. Due to the enolate being a stable carbonyl and a hard nucleophile it favors the attack on the carbonyl of the furfural, a hard electrophile, rather than on the double bond than is conjugated with the carbonyl because the double bond is instead a soft electrophile and is conjugated (stabilized).

Thereafter, the intermediate is protonated by the aqueous solution and undergoes a second deprotonation of an alpha hydrogen by the hydroxide ions in the solution in order to form a trisubstituted carbanion that is resonance stabilized. The following and final step is an E1cb mechanism where the hydroxy group gets eliminated to allow formation of an α, β-unsaturated carbonyl, Product A . The second reaction performed used a Phase-Transfer Catalyst. The role of the catalyst in this reaction is unclear but hypothesized to carry hydroxide ions from the aqueous phase to the organic phase where the ions can help generate enolates that react with the furfural (Lab Manual, 2023). The second reaction follows the same steps that it took to form Product A above. Due to the excess amount of furfural, additional deprotonations of the Product A structure can continue on and attack the furfural to create Product B .

Thereafter, protonation of the negatively charged oxygen will create a β-hydroxy carbonyl. Subsequently, deprotonation of the last alpha hydrogen by a hydroxide group from the solution will form a trisubstituted resonance stabilized carbonyl. Lastly, a second E1cb mechanism occurs to form the second α, β-unsaturated carbonyl within the final molecule after the OH group is forced to leave. Results and Calculations Since cyclopentanone is the limiting reagent for the formation of product B and has a one-to- one ratio of the initial amount with the final product, it is used to calculate the theoretical yield. Product A %yield: N/A Theoretical yield of product A: 50 mmol cyclopentanone = 50 mmol product A 50 mmol product A× 1 mol 1000 mmol × 162.2 g / mol = 8.11 g

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Since the product A obtained as liquid, there’s no theoretical yield applied. Product B %yield: 79.2% Theoretical yield of product B: 10 mmol cyclopentanone = 10 mmol product B 10 mmol product B× 1 mol 1000 mmol × 240.3 g / mol = 2.403 g product B%yield = experimental yield theoretical yield × 100 = 1.903 g 2.403 g × 100 = 123.35% = 79.2% Label Integration value Chemica l Shift Approximate result Number of hydrogen atoms Multiplicity Identity B 0.7 2.07 2 2 d A C 2.01 2.40 2 2 t B D 2.10 2.99 2 2 td C I 0.94 6.52 1 1 dd D K 0.96 6.70 1 1 d E L 0.93 7.17 1 1 t F N 1.00 7.57 1 1 d G Table 1 - Analysis of H NMR of Product A. Label Integration value Chemica l Shift Approximate result Number of hydrogen atoms Multiplicity Identity A 4.00 3.08 2 4 s A B 1.94 6.54 1 2 dd B C 1.96 6.70 1 2 d C D 1.69 7.35 1 2 s D E 1.93 7.59 1 2 d E Table 2 - Analysis of H NMR of Product B.

The melting pint test was not performed and thus the data is not available. Discussion For Product A, there are ten hydrogens in the overall structure. In the H NMR, there are seven signals labelled from A to G on the H NMR Spectrum and as seen in Table 1. For Product B, there are twelve hydrogens in the overall structure. In the H NMR, there are five signals labelled from A to E on the H NMR Spectrum and as seen in Table 2. Chemical shifts from 0 to 2ppm usually belong to methyl, methylene or methine groups. Signals from 1.8ppm to 3.1ppm belong to hydrogens that are on carbons that are adjacent to a double bond, a triple bond, a sulfur atom, a nitrogen atom, an aromatic ring or a carbonyl. Signals from 2.8ppm to 4.9ppm belong to hydrogens bound to halogen or oxygen bound carbons. Signals from 4.7ppm to 7.0ppm belong to hydrogens directly bound to a C=C. With this information, and the concept of shielding and deshielding, hydrogen atoms were assigned to each signal. Due to the conjugated systems in both molecules, all signals are slightly or highly deshielded. In other words, all hydrogens are shifted downfield. The closer a hydrogen is to the conjugated system, a double bond or an oxygen atom, the more deshielded it is and as such the more downfield its signal will be. To continue, the reactions occurred in diethyl ether in order to assure proper protonation and deprotonations occurred. For Product A, addition of aqueous sodium hydroxide would have started the deprotonation of the cyclopentanone. Cooling the reaction mixture was done in order to slow down the rate of reaction perhaps so that upon addition of recently distilled furfural the carbonyl attack was favored. The reaction is stirred in order to assure the reaction occurs homogenously throughout the mixture and kept on ice in order to avoid evaporation of any reagents or intermediates due to the reaction’s exothermic properties. The flask was parafilmed in order to keep any reagents and intermediates, especially diethyl ether, from escaping as well.

When separating, the product is first filtered in order to get rid of any precipitates. The flask must be clean in order to assure that no side reactions occur, for example if acetone was present. The filtrate is kept for further separation while the solid on the filter is discarded. The filtrate is placed in a separatory funnel to undergo extraction with diethyl ether and washing with aqueous sodium chloride. The final liquid is dried with calcium chloride in order to get rid of any residual water or aqueous traces. The solution is left to evaporate for a week. Thereafter, column purification is performed instead of vacuum distillation. This might be because column purification takes less time than the vacuum distillation and gives a better purer yield of product. The column was wet packed with silica, the mixed eluant as mobile phase. Sand was used to ensure the silica gel would not be disrupted, cotton at the bottom of the column to ensure that the sand and the stationary phase would not fall through. Each species of sample interact different time with the stationary and mobile phases which leads to the different retention time in the column then separated and purified final product. To finish the elutant of yellow color was evaporated on a rotary evaporator in order to purify the solution to a larger degree, getting rid of any remaining starting material and residual ether as well as the columns solvent. Since no vacuum distillation was performed, recrystallization was not required. As such, the mass and H NMR were then collected. For Product B, 10 mmol of cyclopentanone was added with diethyl ether. Then the sodium hydroxide, and the phase-transfer catalyst were added, and the mixture was cooled to 5°C which means the polycondensation product was favored. Then the present of catalyst aliquat 336, which also favored the heavier product. And the base OH-, as well as the enolate of cyclopentanone remain in the aqueous phase as they are negative charged hence not dissolved in ether, as such, The phase-transfer catalyst sped up the accessibility of hydroxide ions and as such the reaction was much faster than without the catalyst as experienced when synthesizing product A. In addition, due to the exothermic properties of the reaction evaporation was very likely. As such, the flask was parafilmed to prevent escape of reagents, solvents and any molecules. Vigorous stirring was used in order to assure the mixture was homogenously being reacted. Product B was isolated form the mixture with vacuum filtration. The solid was washed with diethyl ether in order to assure any impurities ended up in the filtrate. It was then air dried to assure all traces of water left. The product was recrystallized based on different solubility between target product and impurities, the desired product can be recrystallized in ice-water bath while the impurities remained in solvent, which lead to the product getting purer and obtained 79.2% yield. Thereafter, the mass and the H NMR of the product are recorded.

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Conclusion This experiment consisted of synthesizing two products by controlling the conditions of the reactions. To make product A, 2-(2-furylmethylidene) cyclopentanone, equimolar conditions were adopted as well as long reaction time. To make product B, 2, 5-bis (2-furylmethylidene) cyclopentanone, excess furfural was used as well as a phase-transfer catalyst to shorten reaction time. In both reactions, ice baths were used in order to minimize loss of product through evaporation due to the reaction’s exothermic properties. There’s no mass recorded since product A obtained as liquid while product B had a much greater %yield (79.2%). In addition, the peaks for product A H NMR: δ 7.57(d, 1H); 7.17(t, 1H); 6.70(d, 1H); 6.52(dd, 1H); 2.99(td, 2H); 2.40(t, 2H); 2.07(d, 2H) while the peaks for product B H NMR: δ 7.59(s, 2H); 7.35(s, 2H); 6.70(d, 2H); 6.54(dd, 2H); 3.08(s, 4H). This experiment can be improved upon by cooling the reactants to the desired 5/10°C before mixing them together. This would decrease the overall temperature of the mixture and prevent loss of product through evaporation. Also, using Teflon instead of parafilm might be advantageous due to Teflon’s inertness to other chemicals and due to parafilm’s ability to dissolve when in contact with diethyl ether. References Klein, D. Organic Chemistry , 2 nd ed. John Wiley & Sons, NJ; p. 973-976. Hunt, I.; N.D.; Chapter 13: Spectroscopy. http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch13/ch13-nmr-3b.html (Accessed October23 rd , 2023) Chemistry 324 Laboratory Manual Organic III: Organic Reactions ; Concordia University: Montreal, QC, August 2023; pp. 63-70 & 221-229. Socratic. 2015. Shielding and Deshielding. https://socratic.org/questions/what-is-shielding-and- deshielding-in-nmr-can-you-give-me-an-example (Accessed October 23 rd , 2018) Wang, W.; Ji, X.; Ge, H.; Li, Z.; Tian, G.; Shao, X.; Zhang, Q.; 2017. Synthesis of C15 and C10 fuel precurssors with cyclopentanone and furfural derived from hemicellulose. https://pubs.rsc.org/-/content/articlepdf/2017/ra/c7ra02396k