Diol Preparation

Weigh 2.15 grams of sodium borohydride on a weigh boat. Bear in mind that sodium borohydride reacts violently with water and may cause serious burns. Handle it carefully.

Place a magnetic stir bar or "flea" in the beaker. Pour the sodium borohydride from the weigh boat into the beaker and transfer it to the fume hood. Perform the remainder of this experiment inside the fume hood for safety.

Place the beaker atop the stir plate. Measure 30 mL of the 95 percent ethanol and add it to the beaker. Stir the mixture gently until all of the sodium borohydride has dissolved.

Place the empty 50 mL Erlenmeyer flask on the scale and zero out the scale so it does not take the weight of the flask into account. Add 2,3-butanedione to the flask until you have 8.61 grams. The 2,3-butanedione is a liquid at room temperature, so you will need to use a Pasteur pipette to transfer it into the flask on the scale.

Fill a plastic bucket with ice and place it in the fume hood near your apparatus. Set up the ring stand and clamp. Connect your thermometer to the clamp so the tip of the thermometer is suspended in the solution in the beaker. Make sure the thermometer tip is not in contact with the magnetic stir bar.

Turn the magnetic stir plate back on to keep the solution mixed. Make sure the thermometer is positioned so that its tip does not come into contact with the stir bar.

Using a Pasteur pipette, add the 2,3-butanedione to the solution a drop at a time. Keep a close eye on the temperature. Do not allow the temperature to creep above 50 degrees Celsius. You want the temperature to stay between 30 and 50 degrees. If you find the temperature has soared a too high, remove the beaker and cool it in an ice bath.

Continue this process until all of the 2,3-butanedione has been added. You should see a white precipitate forming in the beaker.

Allow the beaker to cool for about 15 minutes. Keep the magnetic stir bar on during this time.

Add ~15 mL of the hydrochloric acid to the beaker. Be aware that hydrochloric acid is highly caustic and can cause severe burns or injury.

Let the mixture to sit for a minute, then place it on the hot plate. Heat the mixture to a gentle boil and keep it at that temperature until it separates out into two horizontal layers.

Turn off the hot plate and transfer the beaker to an ice bath to cool it down. Once it's cooled, check the separatory funnel to make sure the stopcock is closed. Remove the stopper in the top and pour the mixture into the separatory funnel.

Rinse the beaker with ~20 mL of diethyl ether and pour this rinse into the separatory funnel. (Note that diethyl ether is EXTREMELY flammable.)

Place the stopper in the top of the funnel. Hold it with both hands, using one hand to keep the stopper in place. Gently tilt it back and forth. Now tilt it backward so the stem points upward. Open the stopcock to release any pressure inside the funnel. It's extremely important not to allow excess pressure to build up since this could cause the stopper to come out. Close the stopcock again and shake the funnel back and forth (more vigorously this time). Tilt it back again and open the stopcock to release pressure. Repeat this procedure until you've shaken it for a total of about 30 seconds.

Allow the two layers to separate. Make sure the stopcock is closed and place the separatory funnel back on the ring on the ring stand. Place a 100 mL beaker beneath the funnel and open the stopcock a little to allow the water layer to drain out. Close the stopcock as soon as all the water has drained out -- you want to keep the diethyl ether layer.

Place the other 50 mL Erlenmeyer flask beneath the separatory funnel and drain the ether layer into it. Pour the aqueous layer back into the funnel and add another ~20 mL of diethyl ether. Repeat Step 14 to mix the two layers, then allow them to separate.

Release the water layer back into the 100 mL beaker. Drain the diethyl ether layer into the 50 mL flask that already contains the first diethyl ether fraction. Pour the diethyl ether back into the separatory funnel (use a glass funnel if needed) and add ~10 mL of water. Repeat step 14 to mix the two layers, then allow them to separate. Drain the water layer into the beaker containing the first water layer. Drain the remaining diethyl ether back into the 50 mL flask.

Add ~100 mg of anhydrous sodium sulfate to the 50 mL Erlenmeyer flask and allow it to sit for 10 minutes.

Decant the diethyl ether into a clean 100 mL beaker and place it on the hot plate inside the fume hood. Heat the solution slightly by turning the hot plate on a low setting. Do NOT overheat -- diethyl ether boils at 34 degrees C. The hot plate should be kept at a very low setting because diethyl ether poses a serious fire hazard. Once the solution has ceased to boil and all the diethyl ether has been boiled off, the remaining liquid is your product.

Clean up your workspace in accordance with your lab guidelines.