This experiment was performed to show how a ketone and an aldehyde could be added together through the aldol condensation. This type of reaction proceeds through the creation of a resonance-stabilized enolate ion from one of the carbonyl groups. The enolate ion can then act as a strong nucleophile and add to another carbonyl group.
It is extremely important that one of the carbonyl groups has an acidic alpha hydrogen one adjacent to a carbonyl group so that the enolate ion can be formed. Aldol products can be formed through either acidic or basic conditions and since they are usually exothermic the reaction will be driven to completion. In this experiment, you will run an aldol condensation between an aldehyde and a ketone and then the product of the reaction precipitates out of solution and can be collected by filtration.
The crude product is normally purified by recrystallization. Weigh your product and determine percent yield. What reactant is your percent yield based on?
Determine the melting point and compare to the literature value. Table 1 and 2 Table 1. If contacted, remove with plenty of water. In a medium size tube, mix 2mL of benzaldehyde with 15 drops of acetone, and leave it at room temperature for 5 minutes.
Then, add the mixture to the ethanol-NaOH solution in small portions and stir with magnetic stirrer if available for 30 minutes. Chill the solution in an ice-water bath. Collect the yellow crystals by suction filtration and hand-dry them by pressing them between dry paper towels. Determine the weight of the dibenzalacetone product, its melting point, and the percent yield.
Return the product to your instructor. NOTE- The amounts of the reagents used in this reaction are very important to ensure the correct product forms. The dissolution is exothermic and the contents of the Erlenmeyer will get warm. Allow the solution to cool before using it. In a 50 ml Erlenmeyer flask weigh out accurately 0. Mix and swirl occasionally for fifteen minutes.
A yellow, flocculent precipitate should form. Filter the solid product by vacuum using your spatula to transfer as much of the solid as possible to the Buchner funnel. Take a TLC at the end of the period. Add 2 mL of H2O into the tube to wash the crystals and remove using a pipette. Repeat 3 times. Run an IR to determine the quality of the product. This could be an indication of low product quality and the presence of impurities in the crystals of the product.
Taking Rf values during the performance of the experiment helps track the progress of the reaction and determine the ending point of reaction. The fact that the Rf value increased from the beginning to the end of the experiment indicates the occurance of the reaction since the product dibenzalacetone is less polar than the reactants acetone and benzaldehyde. The IR spectrum indicates the presence of the desired product. The strong peak at cm-1 is an indication of the presence of the carbonyl functional group.
The peak at cm-1 is an indication of the presence of the double bonds in the product, and the next weak signals are indicators of the presence of aromatic rings.Return the product to your instructor. The following equation is an example of an Aldol beta-hydroxyketones readily eliminate water to form enones. Since we are working with conjugated aldehydes, the resulting condensation: Aldol condensations are important in synthesis synthesis, providing a good way to form carbon-carbon bonds. Using aldol or crossed aldol synthesis, suggest a synthesis. Ethyl acetate is flammable. Determine the melting point and compare to the literature.
Advanced Organic Chemistry 5th ed. Under the reaction conditions in the experiment, two equivalents of aldehyde will react. Recrystallize your product from ethyl acetate using a water bath and hot plate to heat the solvent. NOTE- The amounts of the reagents used in this reaction are very important to ensure the correct product forms. Compound Mol. Berichte der Deutschen Chemischen Gesellschaft in German.
This would give an end product of benzalacetone instead of dibenzalacetone. Introduction Like the Grignard reaction, the Aldol Condensation is an extremely useful carbon-carbon bond-forming reaction in organic chemistry. This is of course quite different than the chemistry of normal alcohols. Annalen der Chemie und Pharmacie in German.
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Allow the solution to cool slowly to room temperature and then cool in an ice bath. Why do you imagine that you obtained the trans isomer as the major, or even sole, product? Draw the structure of the cis and trans isomers of the compound that you prepared.