Question

NaBH4(Sodium Borohydride) Reduction of Ketone (Organic Chemistry Lab)

Questions

1. Explain the reaction mechanism and why each reagent was used.

2. Explain the need for 2 different drying agents

3. Use IR stretches and melting point determination to explain your results.

4. Report sources of error.

Experiment Procedure

1. Assemble the reaction apparatus as shown in Figure 14.2a, consisting of a 3.0 mL conical vial charged with 4-t- butylcyclohexanone (amount calculated in pre-lab) and methanol (100 μL). Attach the air condenser and after shaking the vial to dissolve the ketone, add the borohydride solution through the condenser (300 μL from an Eppendorf pipette).

2. Allow the solution to stand at room temperature for 10 minutes.

3. Chill dilute HCl (0.5 mL, 1 N, measured with your “calibrated” Pasteur pipette) in a small vial. Add this cold acid to the reaction mixture by Pasteur pipette.

4. Extract the reaction solution three times with methylene chloride (0.5 mL each time). After each addition of methylene chloride, cap the vial, shake gently, carefully vent when opening the cap and combine the organic portions in a separate vial.

5. Using a Pasteur pipette, transfer the combined organic portion to a vial containing 200 mg Na2SO4. After stirring this pre-dried solution,

   transfer by pipette to a filter pipette containing a cotton plug and anhydrous magnesium sulfate (500 mg) (see Figure 15-2b) suspended over a tared 1 dram vial. Rinse the vial with additional methylene chloride (0.5 mL) and pass this solution through the drying filter. Dispose of the pipette column in the solid waste container.

6. Evaporate the solvent using the rotary evaporator (p.46). Reweigh your vial to get the mass of the product and determine the melting point of the product. Dispose of the tube in the solid waste container.

7. Add some of the solid sample (10 mg) to a GC vial labeled in marker with your name, sample and section number. Add methylene chloride (1 mL), cap and swirl to dissolve the product. Place your vial in the first available slot in the GC tray, record your name and sample on the GC signup sheet. [Record the tray number in your notebook.]

8. Turn in the rest of the neat product to the TA for IR analysis.

Experiment Results

IR spectra

CD 3500 3000 1000 2500 Wavenumber (cm-1) 2000 1500

Melting point Determination (mp of product ( 4-t- butylcyclohexanol =62-70℃)

experimental product m.p=60-61℃

Answer 1

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