Organic Chem Lab 8: Solventless Aldol Reaction PDF

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Organic Chem Lab 8: Solventless Aldol Reaction...

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Solventless Aldol Reaction

Abstract: The objective of this experiment is to prepare 2-(3,4-dimethoxybenzylidene-(indan-1-one) using solventless aldol reaction. Condensation of 3,4-Dimethoxybenzaldehyde and 1-Indanone took place to yield 40% 2-(3,4-dimethoxybenzylidene-(indan-1-one) which was characterized using Infrared Spectroscopy and by analyzing the melting point.

Introduction The Aldol reaction is a condensation reaction that takes place between carbonyl-containing compounds, in this experiment the two compounds used were 3,4-Dimethoxybenzaldehyde and 1-Indanone. The reaction takes place by a series of steps, the first of which is the conversion of one partner into the corresponding enol or enolate that is catalyzed by an acid or base. Acidic aldol reactions occur through an enol while basic aldol reactions occur via the enolate anion. In this experiment, a base-catalyzed aldol condensation is performed. In an aldol reaction, the enol or enolate anion undergoes a nucleophilic addition to the electrophilic carbonyl group of the second partner. In doing so, the nucleophilic carbonyl partner undergoes an alpha substitution reaction and the electrophilic carbonyl undergoes a nucleophilic addition reaction. The initial product of an aldol reaction is a beta-hydroxy aldehyde which can be dehydrated to form an alpha, beta-unsaturated products known as conjugated anals or enones respectively. Water is lost in the process of the aldol reaction which is why it is known as a condensation reaction. This reaction demonstrates some principles of Green Chemistry, also referred to as sustainable chemistry which is a branch of chemistry focused on the design of chemical products

and processes that reduce or eliminate unnecessary materials, waste generation, and hazards in the workplace. No solvent is used in this reaction, therefore no hazardous chemicals or waste products are being generated. Table1. Physical and Chemical Properties of Chemicals Used Throughout the Experiment Compound

Molecular Formula

Molecular Weight (g/mol)

Melting Point (°C)

Boiling Point (°C)

3,4-Dimethoxybenzaldeh yde

C9H10O

166.176

40-43

281

1-Indanone

C9H8O

132.16

38-40

243-245

Sodium Hydroxide

NaOH

39.997

318

1388

C18H16O

280.32

178-181

N/A

2-(3,4-dimethoxybenzylid ene-(indan-1-one)

Experimental Procedure 0.25 grams of 3,4-dimethoxybenzaldehyde and 0.20 grams of 1-indanone were transferred into a small test tube and were mixed together using a glass stirring rod until the mixture liquefied. After the mixture became liquefied, 0.05 grams of solid NaOH flakes were added into the test tube and mixed until the mixture became solid.. The mixture was then left to stand at room temperature for 15 minutes. Two milliliters of 10% aqueous HCl solution were added to the mixture. Litmus paper was used to make sure the solution was acidic. However, because the litmus paper did not initially turn red more aqueous HCl solution was added. The crude product was isolated using vacuum filtration. The solid was washed with 10 mL of cold water and then air dried for 10 minutes then weighed. The crude product was recrystallized with 20 mL of a hot

90% ethanol/10% water mixture. The recrystallized product was isolated using vacuum filtration. The recrystallized product was washed with 10 milliliters of cold 90% ethanol/10% water solution and then allowed to air dry. The recrystallized product was weighed and characterized using IR and the melting point.

Results

Yield Report Weight of 3,4-dimethoxybenzaldehyde

0.25 g

Moles of 3,4-dimethoxybenzaldehyde

0.00150 mol

Weight of 1-indanone

0.20 g

Moles of 1-indanone

0.00151 mol

Weight of sodium hydroxide

0.05 g

Moles of sodium hydroxide

0.00125 mol

Theoretical yield of 2-(3,4-dimethoxybenzylidene-(indan-1-one)

0.00150mol

Theoretical yield of 2-(3,4-dimethoxybenzylidene-(indan-1-one)

0.4217g

Weight of crude 2-(3,4-dimethoxybenzylidene-(indan-1-one) obtained

0.42g

Actual yield of recrystallized 2-(3,4-dimethoxybenzylidene-(indan-1-one)

0.17 g

Percent yield of 2-(3,4-dimethoxybenzylidene-(indan-1-one)

40%

Melting point of recrystallized 2-(3,4-dimethoxybenzylidene-(indan-1-one)

174.1 - 176.9 ℃

Yield Calculations 0.25g 3,4-dimethoxybenzaldehyde x

1 mol 3,4−dimethoxybenzaldehyde = 1.667 g/mol 3,4−dimethoxybenzaldehyde

3,4-dimethoxybenzaldehyde 0.20g 1-indanone x

1 mol 1−indanone 132.16g /mol 1−indanone

= 0.00151 mol 1-indanone

∴ 3,4-dimethoxybenzaldehyde is the limiting reagent Theoretical yield of 2-(3,4-dimethoxybenzylidene-(indan-1-one)= 0.00150 mol x

280.32g 2−(3,4−DM BA)−(I −1−one) = 1 mol 2−(3,4− DM BA)−(I−1−one)

Percent yield of crude product:

0.42g 0.4217g

0.4217g

x 100 = 99.5%

0.00150

Percent yield of recrystallized product:

0.17g 0.4217g

x 100 = 40%

IR Results  - Peak observed at 2953.90 cm-1  .This peak is indicative of sp3 and sp2 C-H stretching  - Peak observed at 1689.49 cm-1  .This peak is indicative of the ketone functional group.

- Peak observed at 1592.51 cm-1  . This peak is indicative of the aromatic ring Discussion: The objective of this experiment is to prepare 2-(3,4-dimethoxybenzylidene(indan-1-one) using solventless aldol reaction. By analyzing the melting point of the obtained product and using infrared spectroscopy we were able to confirm the successful formation of 2-(3,4-dimethoxybenzylidene-(indan-1-one). The peaks obtained on the IR spectra correspond to the structural components of 2-(3,4-dimethoxybenzylidene-(indan-1-one). A peak at around 2900-3000 cm-1 is indicative of sp3 and sp2 C-H stretching, a peak at around 1700 cm-1is indicative of a ketone functional group, and a peak at around 1500-1600 cm-1, indicative of the aromatic ring. The peaks seen at 2953.90 cm-1  , 1689.49 cm-1  and 1592.51 cm-1  respectively correspond to these expected characteristics. The melting point of the product obtained fell within the range of the expected melting point. The expected point of 2-(3,4-dimethoxybenzylidene-(indan-1-one) was 175-177 and the observed melting point of the product fell within the range of 174.1 - 176.9 ℃ which is not a very broad range is also very close to the expected value confirming the purity of the obtained 2-(3,4-dimethoxybenzylidene-(indan-1-one).

The 3,4-dimethoxybenzaldehyde, which was determined to be the limiting reagent, was used to determine a theoretical yield of 0.4217 g of product. The actual yield of the crude product was determined to be 0.4 g, thus resulting in a percent yield of 99.5%. The yield of the recrystallized 2-(3,4-dimethoxybenzylidene-(indan-1-one) however was 0.17g to give a percent yield of 40%. This low yield can be due to a number of factors; some of the product may have been lost during the transfer from the test tube into the vacuum filtration apparatus or due to possible human error.

Conclusion: The results obtained support that the product formed 2-(3,4-dimethoxybenzylidene (indan-1-one), was obtained from solventless aldol reaction. Although the yield of the product was lower than expected, IR and melting point analysis was able to confirm the successful formation of 2-(3,4-dimethoxybenzylidene-(indan-1-one),

References 1. Libretexts. Aldol Condensation. Chemistry LibreTexts. Libretexts. Accessed November 2019. 2. Roberts, R.M. et al. “Experimental Organic Chemistry” Howard University Edition, Academx Publishing Services, 2014-2015. Pages 187-195....