Aldol Condensation - lab report PDF

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Aldol Condensation Writer: Ryuha Kim Reviewer: Dyllan Skinner Editor: Jude Jaber CH238-A8

Introduction The hydrogen atoms on the carbon adjacent to carbonyl carbon are called α hydrogen. Because of the inductive effect of the oxygen atom on the carbonyl group that acts as an electron-withdrawing group, the acidity of the compound increases. This causes the α hydrogen to be easily removed from α carbon. Carbanion is a enolate anion which can be formed by removing the α hydrogen from aldehydes or ketones. This carbanion acts as a nucleophile and can attack an electrophile. In an aldol reaction, enolate anion reacts with another aldehyde or ketone that acts as the electrophile. Enolate anion attacks partially positive carbonyl carbon on the electrophile in Sn2 fashion. This results in new carbon-carbon bond. Therefore, the aldol reaction is extensively used to lengthen the molecule. The final aldol product is called βHydroxy carbonyl compound. If the aldol product is not isolated and placed in a base for a long time, it loses water and forms double bond through condensation, which is the reason why aldol reaction is called aldol condensation. Finally, the α,β-Unsaturated carbonyl compound is formed. In this experiment, reaction between 1 mole of acetone and 2 moles of benzaldehyde will be performed to produce dibenzalacetone. Benzaldehyde has no α hydrogen atoms so it will act as electrophile while acetone is the nucleophile. This reaction will further dehydrate forming double bond and the final product is dibenzalacetone.

Figure 1. Mechanism of Aldol Reaction between 1 mole of acetone and 2 moles of benzaldehyde in the presence of NaOH to form Dibenzalacetone. Drawn with ChemSketch.

Table 1. Table of Reagents Compound Acetone Benzaldehyde Dibenzalacetone : Cis, cis Cis, trans Trans, trans NaOH

Molecular Weight (g/mol) 58.08 106.12

Density (g/mL) 0.784 1.04

Melting Point (°C) -95 -26

Boiling Point (°C) 56 178.1

234.29

1.1

NA

130

234.29 234.29 39.997

1.1 1.1 2.13

60 110-111 318

NA NA 1388

Experimental In a 10mL Erlenmeyer flask, 0.1mL of acetone and 3mL of ethanolic NaOH solution were added and swirled for 3 minutes. 0.3mL of benzaldehyde and a spin bar were added and the flask was capped with the stopper and boiled for 31 minutes using hot plate. The solution appeared yellow. After about 31 minutes, the flask was removed from the hot plate. The yellow solid was filtered after formed by vacuum filtration using the 25mL side arm filter flask and a Hirsch funnel. The solid was washed with three 1mL portions of cold water. The final water wash was tested with pH paper to make certain it is nearly neutral. It was not neutral, so it was washed with water three times more and allowed to dry on the funnel. The melting point of final solid was recorded. Results Percent Yield = (Actual Yield/Theoretical Yield) x 100% Theoretical Yield: 0.1g acetone x (1 mol acetone/58.08g acetone) x (1 mol dibenzalacetone/ 1 mol acetone) x (234.29g dibenzalacetone/1 mol dibenzalacetone) = 0.403g

Actual Yield: 0.348g Percent Yield = (0.348g/0.403g) x 100% = 86.35% Observed Melting Point: 84°C Discussion The purpose of this experiment was to carry out an aldol condensation to produce dibenzalacetone and determine which of the three possible isomers of dibenzalacetone (cis,cis, cis,trans, and trans,trans) is the major product. The recorded melting point was 84°C, which is close to cis, trans (Z,E) dibenzalacetone with melting point of 60°C. Therefore, the final product was cis, trans (Z,E) dibenzalacetone. The recorded melting point was about 20°C higher, because it contained the other isomer of dibenzalacetone as well. The calculated percent yield is 86.35%. This means that the 86.35% of the acetone has been successfully converted to dibenzalacetone in this aldol reaction. Conclusion In this aldol condensation, 1 mole of acetone and 2 moles of benzaldehyde were reacted with each other to produce dibenzalacetone in the presence of NaOH. Strong base was used to remove the alpha hydrogens of acetone which acted as the electrophile that attacked 2 moles of benzaldehyde. The product underwent to condensation and formed cis, trans (Z,E) dibenzalacetone with melting point 84°C.

Reference 1. Ashenhurst, J., Mukherjee, Mukherjee, S., Ashenhurst, J., Basu, R., Sarmistha, . . . Smu. (2011, December 13). Home. Retrieved from https://www.masterorganicchemistry.com/2011/12/13/evaluating-resonance-forms-3where-to-put-the-negative-charge/ Questions 1. The Dibenzalacetone in the E, E conformation would be recognized as the major product. In the E, E conformation it is seen that it is the most stable form of dibenzalacetone as there is the least amount of steric hindrance present.

2. The attacking of the nucleophile formed in the reaction of acetone and benzaldehyde on the carbonyl carbon of the benzaldehyde. This reaction occurs due to the electrophilic

character of the carbonyl carbon of the benzaldehyde. The electrophilic character is produced as there is a strong presence of the electron withdrawing benzene (also less sterically hindered). Therefore, the reaction will continue and occur in accompany of benzaldehyde instead of another acetone molecule. 3. If 2 moles of benzaldehyde react with 1 mole of acetone give 1 mole of dibenzalacetone. If only 1 mole of benzaldehyde is used, the resulting product is benzalacetone....