Acetophenone and benzaldehyde were then each added

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Acetophenone and benzaldehyde were then each added into the reaction mixture and stirred by way of a stir plate and a magnetic stir bar, this in order to augment the number of interactions between molecules and by extension, maximize product formation. The reaction mixture was then subsequently cooled in an ice bath in order to induce crystallization, which works based on the fact that the amount of solute that can be dissolved scales with temperature. As a result, at cooler temperatures, the solution is saturated at a much lower concentration of solute. The solute which could no longer be held in solution, in this case crude benzalacetophenone, was then recovered in the form of crystals via suction filtration, which exploits the size difference between the crystals and the molecules forming the liquid solution and in turn allows for the crystals to be recovered in the Buchner funnel. At this point a first TLC and melting point analysis were completed in order to serve as comparison points against more pure crystals isolated shortly thereafter. The process of recrystallizing the retrieved crude product was then undertaken. This involved first dissolving the product in boiling ethanol. As mentioned above, this allowed for the maximum amount of solute to be dissolved because solubility scales with temperature. The solution was then cooled, first at room temperature and then afterward in an ice bath to induce precipitation. Suction filtration was then used again, and a small sample of the isolated crystals were then taken for TLC and melting point analysis.
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Part B of this experiment explored the haloform reaction. This reaction involves a methyl ketone reacting with a halogen (Cl 2 , Br 2 , or I 2 ) in the presence of NaOH to yield a haloform and a carboxylate. Similar to the aldol reaction studied above, this reaction also begins with a hydroxide acting as a strong base, which initiates the mechanism by deprotonating an - hydrogen from the methyl ketone. Once again, the reason this hydrogen is acid is due to the fact that the conjugate base formed is stabilized by way of resonance. As a result, we from the enolate ion. This in turn reacts with our halogen and yields a product where we’ve simply replaced an -hydrogen with the given halogen present in solution. This process then repeats itself until all alpha-hydrogens have been replaced as described. Haloform reactions form the basis of the iodoform test which was commonly used in history as a chemical test to determine the presence of a methyl ketone, or a secondary alcohol oxidizable to a methyl ketone.
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  • Fall '10
  • FLYNN
  • Chemistry, Sodium hydroxide, Aldehyde, Aldol Product

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