Lab E Aldol Updated PDF

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Aldol lab...

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Lab E: Aldol Condensation: Synthesis of 2,3,4,5Tetraphenylcyclopentadienone The ability to form carbon-carbon bonds is an important technique in organic chemistry. In the Grignard Lab, we formed C-C bonds by synthesizing triphenylmethanol from a Grignard Reagent. This week, we will employ a different method, the aldol condensation, to synthesize tetraphenylcyclopentadienone. The techniques used in this lab are ones with which you have become familiar throughout this course. By this point in the session, you should be able to read an experimental and go into lab having figured out the amounts of reagent and types of glassware that you need to use. Be sure you come to class prepared. In this reaction, a C-H bond in diphenylacetone is deprotonated, forming a carbon nucleophile that can then add to a ketone. The resulting alcohol may then be dehydrated. We will be performing a double aldol condensation with diphenylacetone and benzil using KOH as a catalyst. The resulting product, 2,3,4,5tetraphenylcyclopentadienone, is a highly colored molecule.

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Experimentally, it is necessary to use a solvent that will be able to solubilize both the base (in our case KOH) and the organic substrates (benzil and diphenylacetone). Furthermore, it is necessary that the solvent have a high enough boiling point that the reaction will occur at a reasonable rate at the reflux temperature. For this reaction, ethanol fulfills those criteria. Tetraphenyl cyclopentadienone (1): Benzil (2.0 grams, 1.0 equiv) and diphenylacetone (1.0 equiv) were dissolved in ethanol (40 mL) and KOH (0.45 g) was added. The mixture was refluxed 15-30 min until everything was dissolved. After cooling to 5 ºC, the crystals were collected by vacuum filtration, washed with ethanol (3×5 mL) and dried to give the product as dark purple crystals.

Before lab in your notebook: You need a title, a graphical drawing of the reaction, and a reagents table. The reagents table should include benzil, diphenyl acetone, and KOH (mass, molecular weight, mmoles, equivalents). You need to include the hazards of KOH, and the boiling point of ethanol.

Prelab Questions to be answered in your notebook: • What size flask should you use? What type of flask should you use? • What would happen if you started timing your reaction before the mixture was actually refluxing? • What color do you think the washing will be? What color will the crystals be? The following data MUST be recorded in your notebook. • The theoretical yield of tetraphenyl cyclopentadienone • The mass of tetraphenyl cyclopentadienone • The percent yield tetraphenyl cyclopentadienone. Study Questions (not to be answered in your notebook): • In this lab, KOH is used to deprotonate a C-H bond. Generally speaking, H atoms bound to carbons are not considered very acidic. Why is this C-H bond acidic enough to be deprotonated by KOH? • What causes color in organic compounds? • If your compound appears purple, approximately what wavelength of light does it absorb? • Does the equilibrium between KOH and diphenylacetone favor the deprotonated form?...