Question

In the second laboratory experiment (Day 2), the depolymerization of polyethylene terephthalate (PET) to the monomer terephthalic acid involves hydrolysis-type chemistry. A mechanism for this conversion is shown in Figure 8. The reaction employs potassium hydroxide, which undergoes nucleophilic addition to the PET polymer. The resulting tetrahedral intermediate can collapse with proton transfer to generate an alcohol byproduct and form a new carboxylic acid species. Under the basic reaction conditions, the resulting carboxylic acid undergoes deprotonation to give the corresponding carboxylate anion. The remaining esters can undergo hydrolysis in a similar manner to disrupt the polymer network. Eventually, with an acidic workup, terephthalic acid is obtained. он hydroxide nucleophilic attack Collapse of tetrahedral intermediate PET carboxylate anion он он Deprotonation Repeat to degrade polymer; electrophilic ester remains can further react with hydroxide nucleophile then, acidic workup erephthalic acid Figure 8. Mechanism for depolymerization reaction performed (Day 2 experiment)

2. Reaction Workup: After 30 minutes of heating and stirring at 130 °C, carefully remove your vial from the heat source and allow it to cool to room temperature in your hood. After cooling, add 5 mL of deionized water to your reaction mixture and allow the mixture to stir for 1 minute at room temperature. Note: most solids in your flask should dissolve, unless there remain some unreacted PET pieces . Pour the contents of your scintillation vial into a 60 mL separatory funnel. Rinse the scintillation vial with 5 additional mL of water to facilitate quantitative transfer of product. Gently mix the contents, cap the separatory funnel, and then shake / vent reiteratively. Allow the layers to settle and collect the bottom (aqueous) layer in an Erlenmeyer flask. Leave the organic layer in the separatory funnel and extract it again with 10 mL water. Combine the aqueous layers

Question:

5. (3 points) You will be doing an aqueous workup with pentanol as the organic solvent. Identify each layer of the extraction (organic or aqueous). Which layer (top or bottom) do you expect will contain your product?

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