Purification of Isoprene
Figure 1: A short path apparatus
Figure 2: A reaction vessel for cleaning Isoprene
Figure 3: A flask for storing and measuring Isoprene
Separate attachment
Figure 4: A round bottom flask
Step 1: Materials required and apparatus set up
-Schlenk line with a short path attachment (figure 1)
-A round bottom flask with required amount of Isoprene and a stir bar (figure 4)
-Reaction vessel (figure 2)
-Storage vessels (figure 3)
-Liquid nitrogen Dewar
-Water bath (Temp. not higher than 40˚C)
- N-Butyl Lithium
-A gas-tight syringe
-Butane Torch
PPE REQUIRED: LAB COAT, FACE SHIELD, FACE MASK, SAFETY GOGGLES, HAND
GLOVES, CLOSE TOE SHOES
Step 2: Freeze-Pump-Thaw
1. Fill beaker (figure 4) with desired amount of Isoprene and a stir bar
2. Use vacuum grease and attach a Schlenk line adapter to the beaker
3. Attach this to short path on Shlenk Link (figure 1), using valve (1)
4. Use a blank glass flange in valve (2) to seal Schlenk Line
5. Using an expandable stand put the Isoprene in a liquid nitrogen bath
6. Wait until it freezes completely
7. Vacuum out the air in the beaker. When opening valve (1), check to make sure there are no
bubbles forming or the pressure reader doesn’t show pressure increase over time. If this is the case,
close the valve and freeze longer.
8. When steady state is achieved, close valve (1) (At least <50 millitorr)
9. Remove the liquid nitrogen bath, and after waiting about 5 minutes, place the Isoprene in a
Luke warm water bath
10. While melting the Isoprene, make sure to stir vessel to remove all dissolved gas
11. After all Isoprene is melted, repeat steps 5-10 twice more. (3 times total), atlast keep the
valve of this vessel closed.
12. Attach a reaction vessel (Shown in figure 2) to valve (2).
13. Vacuum this new vessel, and then flush with argon (5 PSI is good). Repeat 3 times.
14. Vacuum again, and use a butane torch to heat up the glass and remove water residue.
15. After vessel has cooled down, use STEP 3
16. After this, place the vessel in a liquid nitrogen bath.
17. Slowly open valve (1). Make sure Isoprene is not boiling out of control or splashing out of the
beaker. If so, close the valve and try opening slower, or less.
Step 3: Cleaning with N-Butyl Lithium
N-Butyl Lithium is an extremely powerful oxidizer. Take care not to expose to air or heat.
When Isoprene is being cleaned with N-Butyl lithium, the vessel cannot exceed 5˚C or it
will explode violently. Before starting reaction make sure there is enough ice on hand to
keep the reaction at 0˚C. Also, use caution with the Shlenk line when cleaning. Opening a
valve to atmosphere during the cleaning stage can have catastrophic consequences.
Use secondary PPE when handling N-Butyl Lithium such as a face shield, and extreme
caution.
Mixture of N butyl Lithium and Isoprene should always stay at 0˚C
1. Now open the Argon valve on the schlenk line and open the RB vessel secondary valve to
flush Argon at high pressures. Make absolutely sure that argon is flowing and no air can get
into the beaker. With this open proceed to next step.
2. N-Butyl Lithium bottle should first be secured using a three-pronged holder.
3. Using another port on the Schlenk Line, attach a syringe for argon purge.
4. Open the lid of the N-Butyl Lithium, and place the syringe inside, but not in the liquid.
5. Let purge for 30 seconds.
6. Place clean gas tight syringe in bottle without plunger, but not in liquid and let purge for 2030 seconds.
7. Insert plunger and push all the way in
8. Put the syringe tip in N-Butyl Lithium and take an excess amount
9. Carefully turn syringe upside down with the tip still in the bottle
10. Push on the syringe to remove the air bubbles and get the desired amount of Di-Butyl
Magnesium
11. Carefully remove the syringe from the bottle, and if you have a lab partner have them close
the bottle
12. With the argon on constantly, Put syringe tip in the open part of the beaker, and slowly add
N-Butyl Lithium, then close secondary valve on vessel
13. Close the Argon supply on schelnk line and open the vessel to vacuum
14. Meanwhile, close the bottle. Place it back in desiccator, and put the argon syringe inside the
desiccator with the lid cracked open purge for several minutes, then place it back in the
chemical fridge
15. Wait till the Pressure reads <50 millitorr, close the valve for the short path and then do
Isoprene distillation from old vessel to this new vessel
16. For this, place the RB vessel with N-Butyl Lithium in LN dewar and open the valve for RB
vessel with Isoprene in it.
17. For faster distillation, put the RB vessel with Isoprene in luke warm water bath and do not
heat
18. Then, close the valve, thaw it and place it Ice bath and stir it
19. Let it react for 2 hours, making sure to keep the vessel at 0˚C with an ice bath
20. Repeat the purification step with N-Butyl Lithium for one more time
21. When you distill it for second cleaning, make sure the RB vessel with N-Butyl Lithium and
Isoprene is in ice bath while doing distillation.
22. After second cleaning, place a clean graduated cylinder (figure 3) with Shlenk line adapter in
valve (1). Make sure it is large enough to hold all of the Isoprene. Also, make note of the
weight of the vessel before attaching it to the Shlenk Line.
23. Using the same technique as before, vacuum valve (1), purge with argon, repeat, then
vacuum and torch. Pressure should be below 70 millitorr for each cycle.
24. After cylinder is cool, place in liquid nitrogen.
25. After several minutes, open valve (1), then valve (2).
26. As with before, make sure Isoprene is not boiling out of control, or splashing out of the
beaker.
27. When no Isoprene is left, clean the empty beaker with the same technique as in steps 27-28.
28. Place the Isoprene directly into the freezer. Label with date created, who created it, and how
much it is.
Step 4: Vacuum Distillation
Do not heat Isoprene. You may use room-temperature water, but only shortly. Keep Isoprene in freezer
when not in use.
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2.
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7.
Place the cleaned Isoprene in valve (1), and an appropriate vessel (figure 3) in valve (2).
Use vacuum, purge, torch method to clean 2nd vessel and short path.
After cooling, Place valve (2) in a liquid nitrogen bath.
Slowly open valve (2), then valve (1).
Make sure Isoprene is not boiling violently or splashing out of the vessel.
When the amount desired has been collected, close both valves.
Place Isoprene reservoir back in chemical freezer.
Tip: The measurements on graduated cylinders are not accurate. The most accurate way to measure
Isoprene is weighing before / after.
To make small adjustments or get a precise amount, use vacuum distillation in reverse. Fill the smaller
vessel with excess Isoprene. Then, place the larger container in a liquid nitrogen bath, and leave the
smaller one to room temperature. Because you can see the Isoprene level in the vessel you need a
precise amount in, it is easier to stop at a desired amount.
Step 5: Cleaning spent vessels
N-Butyl Lithium Neutralization:
CAUTION: This whole process should take at least 10 minutes. DO NOT RUSH
Be sure all valves are closed and remove the empty di-butyl magnesium flask
Pour tetrahydrofuran (THF) into spout at top of flask
Gently open the valve, the THF will get pulled into the flask as a result of its evacuated state
Close the valve as soon as all THF is injected and swirl contents
Place more THF in spout and gently open the valve again to inject and then close the valve and swirl
Continue this cycle until the flask has achieved atmospheric pressure
Now with the top valve open add THF in copious amounts, remembering to swirl
(~10 mL THF / 1 mL di-butyl magnesium solution used)
After THF has neutralized the di-butyl magnesium; add Isopropanol, then Ethanol, then Methanol, then
Water, and finally Weak Acid. DO NOT RUSH, di-butyl magnesium is potentially explosive with
water/air if it not properly neutralized.