Aldol Condensation Synthesis of Dibenzalacetone PDF

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Aldol Condensation Synthesis of Dibenzalacetone 2020 Summer Term: CH 238 – G5-6 July 2, 2020 TA: Miranda Trentle

Lead Author: Ghaida Almamari Reviewer: Jorge Bonnet Editor: Alyssa Peppers

Introduction: One of the most common method used to form carbon-carbon double bond is Aldol condensing. The word “Aldol” came from the first part of the word “Aldehyde” and the last part from the word “Alcohol”. Aldol condensing reaction refers to organic reaction where an aldehyde with α-hydrogen react with base to form β-hydroxy aldehyde [1]. In this experiment, one mole of acetone will react with two moles of benzaldehyde with presence of NaOH to form dibenzalacetone [2]. During Aldol condensing reaction there is a possibility that Cannizaro reaction occurs, if the OH- attack to benzaldehyde rather than the enolate anion formed from acetone [3]. Below is an expiation the mechanism of Aldol condensing reaction.

Figure 1: Hydrogen atom on a carbon in carbonyl compound are easily removed by a base to form carbon anion

Figure 2: Anion attacking to partially positive carbonyl carbon in the aldehyde or a ketone to form a new carbon-carbon bond.

Figure 3: A mole of H2O is lost and the α,β-unsaturated carbonyl compound formed in Aldol Condensation reaction.

Figure 4: 1 mole of acetone will react with 2 moles of benzaldehyde with presence of NaOH to form dibenzalacetone

Compound Acetone Benzaldehyde Dibenzalacetone

Table 1: Reagent Table Density (kg/m³) MW(g/mol) 784 58.08 670 106.12 234.29

BP(C°) 56 178.1 130

MP(C°) -95 -26 111

Result: Below are the results for the condensing acetone and benzaldehyde forming dibenzalacetone. Mass of watch glass = 32.655 g Mass of watch glass and product = 32.732 g mass of the product =32.732-32.655=0.077 g Melting point range: 94-97°C Moles of benzaldehyde used = 0.1 mol Moles of acetone used = 0.05 mol Moles of dibenzalacetone produced = Moles of acetone used = 0.05 mol Theoretical weight of dibenzalacetone produced = 0.05 mol * 234.29 g mol-1= 11.7145 g Percentage yield of dibenzalacetone = 9.5587 g / 11.7145 g × 100 % = 81.60 %

Figure 5: FTIR of dibenzalacetone:

Figure 6: Aromatic region of pure Dibenzalacetone with coupling constants

Figure 7: Pure Dibenzalacetone

Discussion: Condensation is joining two molecular by losing a small molecular; water usually. Aldol condensing is the condensation of acetone and benzaldehyde forming dibenzalacetone. As shown in Result recorded melting point is 94-97°C, which is closer to the Trans-Trans dibenzalacetone 110-111°C, and the small differences could be caused by impurities like forming the minor products which have melting point around 25-60°C.The NMR spectrum confirm that the product is trans-trans dibenzalacetone, by the location of double bond. Conclusion: From this experiment, it can be concluded that by reacting one mole of acetone and two mole of benzaldehyde, three dibenzalacetone isomers is formed. The recorded melting point is 94-97°C, which is closer to the Trans-Trans dibenzalacetone. This experiment could be labelled as “successful” due forming dibenzalacetone successfully. Impurities could cause the verity of the recorded melting point 94-97°C to the original melting point 110-111°C. Question: 1) Draw all three possible isomers of dibenzalacetone. Which one is likely the major product and why?

The first one is more likely to be the major product because the double bond are in E, which is the most stable form (less steric).

2) In the synthesis as described, why does the enolate of acetone react with benzaldehyde rather than another molecule of acetone? Think about the reaction stoichiometry. Aldehyde carbonyl is more reactive than the ketone carbonyl and the entoleted will not react with the acetone until all benzaldehyde reacts.

3) A student carries out the synthesis but instead of reacting 2 moles of benzaldehyde with 1 mole of acetone, they react 1 mole of benzaldehyde with 2 moles of acetone. What product is most likely to form? Same product, but product yield is reduced because of the 2 mole of acetone reacts with one mole of benzaldehyde. For 1 mole=(1*1)/2=1/2=0.5, 0.5 mole of acetone reacts producing 0.5 mole of product. 2-0.5=1.5 mole acetone left.

References:

1- Admin. Aldol Condensation - Mechanism, Crossed Aldol Condensation, FAQs https://byjus.com/chemistry/aldol-condensation/ Access July 2.2020 2- Nikles, Jacqueline A. Aldol Condensation Synthesis of Dibenzalacetone. University of Alabama at Birmingham, Birmingham, AL. Access July 4.2020 https://uab.instructure.com/courses/1527303/files/63508358?module_item_id=15586968

3- Nikles, Jacqueline A. Pre-Lab Lecture Aldol Condensation. University of Alabama at Birmingham, Birmingham, AL. Access July 4.2020. https://www.google.com/search? client=safari&rls=en&q=Pre-Lab+Lecture+Aldol+Condensation&ie=UTF-8&oe=UTF-8...