I am searching for reactor set-up that can maintain inert atmosphere, and found that many organic synthesis labs use Schlenk line. But organic synthesis is not main thing of my lab, so there is some difficulties (especially for vacuum pump) for setting up Schlenk line. Therefore I have searched for method that doesn't use vacuum pump, and I found this video.


There are some questions.

  1. At 0:44, he pushes the red rubber-like thing to the oil bubbler and call it 'pipette bulb'. Pipette bulbs I know is two kinds. (see images below)

enter image description here

Is that second one? It seems a little bit different. And what is the role of pipette filler? Does it just let the gas to go to the oil?

  1. At 1:01, he push Pasteur pipette to the adapter. What is that adapter? When I search for 'Pasteur pipette adapter', I found this.

enter image description here

It seems similar, but it doesn't have white screw-like thing.

  1. At 2:06, he says that the end of the pipette should be under the surface of the liquid. I usually conduct synthesis in 10~100 mg scale, with about 10 mL of solvent. So it is hard for Pasteur pipette to reach the surface of liquid. Should I just find a smaller flask? (I usually use 250 mL three-necked flask)

  2. At 2:06 he starts purging and at 2:35 he ends purging. How can I determine when to end the purging?

  3. At 2:47, he removes the tube from adapter and connect it to the pipette bulb. Then is he supplying the inert gas to the oil bubbler continuously?


(Check again if your lab has not a Schlenk line or if one may be purchased, manufactured (your local glass blower), acquired (ebay-like second hand), or shared with your befriended group across the aisle. Because it is a tool equally used in inorganic chemistry, catalysis, etc. Then read a guide like this one to have some general idea, and get an instruction in person by an chemist more experienced with the design you will work with.)

The video omits one approach consisting of mounting the air dry glass ware in first place, to thoroughly dry the setup with a heat gun (a powerful hair dryer), and to allow the setup to cool to room temperature while being purged by inert gas. The drying is more efficient if the setup is evacuated and if proceeding from the inlet of the inert gas to the venting outlet. If the setup includes a condenser, then no water is allowed in the coil of the condenser during the drying. If you have the option, argon may create a blanket on top of your reaction (thus, you may save some volume of inert gas), while the cheaper nitrogen by relative density goes off to the exhaust. Note, nitrogen equally may react with some metals (e.g., Li, Mg).

After this to your questions:

  1. He briefly closes one branch of the T either with a stopper, or rubber bulb. Don't use the Peleus sphere shown on the left hand side. The oil in the bubbler is a visual for the pressure inside the setup, and a safety valve should the pressure in the setup increase too much.

  2. The left-hand side of the adapter shown by you looks more like a silicon tubing, than glass. Look for a thermometer adapter / inlet like the following:

    enter image description here

    (adapted from here)

    Below the cap you find an o-ring. With loosened cap, push the Pasteur pipette through, then tight the cap gently and mount the adapter. But in many cases, a normal knee-shaped adapter may work fine to connect your setup with the inert gas, too.

  3. One word: scale. Except if you really need to work at low concentrations (say below $\approx \pu{1 mol/L}$), use a smaller flask. For safety (e.g., sudden evolution of gas, foam) and comfort (intentional quench of the reaction, start of workup), it is nice to use about 40% of the flask's volume by the volume of reaction. Thus, consider a smaller flask e.g., $\pu{25 mL}$. This equally reduces the space needed in the hood, eases drying the setup, monitoring temperature, etc.

  4. If there is no flow indicator for the inert gas, connect a hose with the inert gas supply and a Pasteur pipette and set up once a pneumatic trough. This gives you an estimate how much time is needed to replace x-amount of gas in the setup if no vacuum was applied earlier. If you evacuated the setup (pump-thaw cycles, requires gentle greasing the joints), then the bubbler indicates when you reached normal pressure in the setup.

  5. I can not recommend this change of the setup. Mounting the inert inlet on one wing of the T, across the exhaust, no longer guarantees protection by the inert gas. Instead, it will flow the path of least resistance regardless what happens below the reflux condenser and round bottom flask.

    Instead, 1) keep the inlet remote from the exhaust of the setup, 2) maintain a very low but steady flow rate to prevent air and humidity from entering the reaction flask. If you don't aim to distill-off solvent (especially at reduced pressure), then you don't constantly blow nitrogen / argon into your reaction (it is not a fish tank). You do not want to waste of inert gas, nor evaporate your solvent of reaction during the reaction.

  • $\begingroup$ Thank you for detailed answer. May I ask some more questions? 1) As I calculated, the concentration in my reaction volume is about 0.03 M. You mentioned that 'except I work at low concentration' I had better use a smaller flask. Then in this situation, I have to use a flask bigger than 25 mL? Is that okay to use 100 mL or 250 mL? 2) I'll consider with lab seniors to set up Schlenk line. But first, is it okay to use setup without vacuum like the video I uploaded, despite some low quality than Schlenk line? $\endgroup$
    – Krang Lee
    Jul 30 at 1:46
  • $\begingroup$ 3) Honestly, when I search for other Schlenk line videos, I don't understand heating glasswares (some heated with torch) is of importance. Is this procedure very essential and important? 4) Why does the constant flow of inert gas let the solvent to evaporate? (I don't understand the principle) Is it okay to remove the flow once the inside of the flask reach normal pressure? I thought that constant flow is necessary because anyway top of the reflux condensor is open to the air. Is this removal of constant flow same procedure when I use Schlenk line? (actually when I took over this synthesis, $\endgroup$
    – Krang Lee
    Jul 30 at 1:51
  • $\begingroup$ senior supplied constant flow of inert gas to the septum, for 24 hours of reaction time) I think that inert atmosphere can be broken for 24h or more reactions. $\endgroup$
    – Krang Lee
    Jul 30 at 1:55
  • $\begingroup$ 5) I have flow indicator with cc/min unit. Then I don't need pneumatic trough? How much flow should I set up and how can I know if inside the flask reached normal pressure using bubbler? (sorry for too elementary question) $\endgroup$
    – Krang Lee
    Jul 30 at 2:13
  • 1
    $\begingroup$ @KrangLee Continuation in the chat room The Periodic Table. $\endgroup$
    – Buttonwood
    Jul 31 at 16:15

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