-Evan’s aldol reaction(post lab)

EXPERIMENTAL PROCEDURE
Note: All glassware and stirring bars are dried in an oven overnight (100–120 °C) prior to use.
Representative example of a reaction apparatus setup
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1. Start by preheating an oil bath or heating block to 95 °C.
2. Add a small stirring bar and (S)-valinol (1 g, x mmol) into a 5 mL round bottom flask.
3. Add potassium carbonate (x g, 0.1 equiv).
4. Add diethyl carbonate (x mL, 2 equiv).
5. Ensure that there is minimal solid reagent at the ground glass joint area. Wipe clean
with a Kimwipe if necessary.
6. Place a Hickman distillation head on the round bottom flask and attach a water
condenser.
7. Seal the top of the water condenser with a rubber septum.
8. Purge *
the reaction system with nitrogen gas for ~2 min and maintain an inert
atmosphere.
9. Using an oil bath or a heating block, heat the reaction mixture to reflux. Monitor the
temperature of the oil bath or heating block, which should be set between 95–100 °C.
The heating source should not exceed 100 °C.
10. Ethanol will condense in the Hickman head.
11. Using a Pasteur pipette, remove ethanol (EtOH) occasionally and measure its weight to
determine when the reaction is complete.
12. Pay attention to the volume in the round bottom flask and do not let it boil dry. Add more
diethyl carbonate if necessary and record this in your lab notebook.
13. Monitor the reaction by TLC every 20 min. Try developing the TLC with 100% ethyl
acetate (EtOAc) and a 1:1 mixture of acetone/hexanes. Modify the solvent system to
obtain an Rf ~ 0.3 for the product.
14. When EtOH evolution ceases or when TLC indicates complete consumption of the
starting material (this should take approximately 1 h from the time of heating), allow the
reaction mixture to cool to room temperature.
15. Dilute the product mixture with dichloromethane (~2 mL) and transfer the content to a
10 mL test tube. Rinse the round bottom flask with additional dichloromethane (~1 mL)
and transfer this to the test tube. This is the organic phase (aka organic layer/portion).
16. Wash the organic phase with brine solution (~1.5 mL or approximately half the volume
of the organic layer), using the Pasteur pipette as a mini separatory funnel.
Combine and set the aqueous phases aside for now. Do not discard until you have
confirmed that the desired product is in the organic phase.
17. Dry the organic phase with anhydrous sodium sulfate and filter the solution into a clean,
tared vial.
18. Concentrate the solution on a rotary evaporator (rotovap). Note the appearance and
record the yield of the product.
19. Recrystallize the product from hot 1:2 hexanes/EtOAc and collect the crystals by
vacuum filtration. (If time permits, instead of using a mixture of 1:2 hexanes/EtOAc,
recrystallize by first dissolving the crude product in a minimum volume of hot EtOAc,
and dropwise add hot hexanes until the mixture becomes cloudy. Then cool the mixture
– first to room temperature and then in an ice bath).
20. Record the 1H and 13C NMR spectra, IR spectrum, as well as the melting point of the
crystals.