The above video is a general overview of a typical Schlenk line in our lab. The position of some of the ports/valves may differ from one Schlenk line to another but they are similar enough that this video of the Fumehood #1 Schlenk line should serve equally for all the lines in our lab.
GENERAL SCHLENK LINE USE
1. Preparing flasks for "Air-Free" use: The term "air-free" is used loosely, in our group at least, to indicate systems that do not contain any oxygen and often it is also assumed to mean water free as well, although the latter should be clarified before you perform a react and in your experimental write-ups to avoid confusion. One method to make a flask or other container ready for air-free work is to bring it into the glovebox but in general we will be using the Schlenk line for most air-free work. Below is the general methods for preparing flasks for air free work.
Initial Preparation of any flask for Schlenk line use: the glassware to be used must have been in the oven overnight prior to use so as to have it dry to begin with (i.e. water free). If you are using a magnet stirbar this should also be dried overnight, in general one just puts the desired stirbar in the flask in the oven. Remove the flask from the oven, immediately place a septum over the flask (DO NOT put the septum in oven - just get it from the drawer) and then bring it to the Schlenk line. Note, in consultation with Dr. Daley, at times you may be able to use a flask that has been in the oven for 3-4 h as long as it is subjected to a heating protocol on the Schlenk line before use (see Here). if you are start.
(a) Connecting flask to Schlenk line: the two most common types of flasks you will encounter are regular glassware (e.g. round-bottom flasks, pear-shaped flasks, or even 3 dram (20 mL) vials and other containers like that) and specialty "air-free" glassware (e.g. side-arm flasks and Schlenk tubes), which are both pictured below.
For non-side-arm glassware:
(i) Get a Luer-Lock to hose metal adaptor (also pictured below) and connect it to a hose of the Schlenk line.
(ii) Attach a stainless steel needle that has been dried in the over overnight, to the Luer-Lock adaptor. We have several sizes of needle (both diameter and length) so you will choose the most appropriate one to use. As example, for a small neck flask (14/20 neck) one would use a smaller diameter needle (higher gauge; 20 usually but possibly 22) so as not to make big puncture holes in relation to the septum size. For large neck flasks (24/40) one usually uses larger diameter needles (lower gauge; 18 usually but sometimes 16).
(iii) Open the Schlenk line stopcock adaptor to nitrogen gas, making sure the bubbler is still bubbling (i.e. still positive pressure in Schlenk line), and let it flush for 15 seconds or so to flush out the needle.
(iv) Stick the needle into the septum of the flask by pushing it through the septum while holding the needle close to the sharp-end. Holding it closer to the tip allows you to have more control over the needle and lessens the likelyhood that you will bend and/or break the needle.
(v) With the needle in the flask, turn the stopcock valve to the closed position of the Schlenk line (position handle parallel to the tabletop) and continue to turn it to open it to the vacuum line. Do this slowly.
(vi) Leave the flask under vacuum for, ~5-10 minutes, until the flask cools to room temperature.
The flask is now ready for the purge-fill cycles (see section (B) "Purge-Fill Cycling" below).
For side-arm glassware:
(i) Simply attach the side-arm connector to the hose of one of the Schlenk line ports. Make sure when attaching the side-arm connector to the hose that you DO NOT TWIST THE HOSE OVER THE GLASSWARE ARM!! The glass can easily shear with sharp edges being produced and thus it is a significant hazard for deep cuts. So please becareful and use an "up-down" movement of the hose with inline pushing or pulling to get the hose on or off the glassware, respectively.
(ii) With the side-arm stopcock in the closed position, open the Schlenk line stopcock adaptor to the vacuum line.
(iii) Slowly open the side-arm stopcock.
(iv) Leave the flask under vacuum for, ~5-10 minutes, until the flask cools to room temperature.
The flask is now ready for the purge-fill cycles (see section (B) "Purge-Fill Cycling" below).
(b) Purge-Fill Cycling: this is a method you will use continuously in the Daley group. It is the critical step to having "air-free" conditions on the Schlenk line. So, PLEASE MAKE SURE YOU DO THIS PROPERLY! I encourage you to look at the video at the bottom of this section for a refresher on the technique as well.
Non-side-arm glassware:
(i) Connect the glassware to the Schlenk line and put it under vacuum as described in Part (a) "Connecting flask to Schlenk line" above.
(ii) Turn the Schlenk line stopcock to the closed position (parallel to tabletop) and then SLOWLY turn it to the open position to the nitrogen manifold.
(iii) Watch the bubbler; when the valve is opened, the bubbling will cease or its bubbling rate will decrease while the nitrogen fills the evacuated hose and attached glassware. The bubbling should return to its normal rate within a 5-30 seconds depending on the size of the flask. At this point the hose is under a nitrogen atmosphere at atmospheric pressure. Going slowly will also make sure you do not disrupt the contents of the glassware (specifically if the contents are dry solids that can swirl up in the nitrogen gas stream entering the flask and potentially go up into the septum or other inconvenient places in the glassware). If you notice the oil is being sucked back up the bubbler, quickly close the valve as there is insufficient nitrogen flow. Partially close the bubbler valve to increase the flow/pressure of nitrogen and then open the side-arm valve as before. Wait until the bubbling returns to its normal level.
(iv) Turn the stopcock of the Schlenk line to the closed position and then turn it SLOWLY to the open vacuum position. Open it slowly so as not to disrupt the contents of the glassware (specifically if you have a solution, as bumping can occur). Open it only partially and wait to ensure the contents of the glassware are not disrupted. After about 5-10 seconds you can open the stopcock fully if no disruption is observed. Leave the flask open to vacuum for 5-15 minutes (5 minutes for smaller glassware through to 15 minutes for larger glassware). Leaving it longer (ideally 20 minutes) is not a bad thing but these times will make it reasonable for one to perform a reaction in a reasonable amount of time available to most undergraduates.
(v) Repeat steps (ii) through (iv) at a minimum of TWO more times, ideally FOUR more times.
(vi) Finish the cycle procedure by returning the glassware to a nitrogen atmosphere by repeating steps (ii) and (iii). The system is now air-free!
Side-arm glassware:
(i) Connect the glassware to the Schlenk line and put it under vacuum as described in Part (a) "Connecting flask to Schlenk line" above.
(ii) Close the side-arm valve.
(iii) Turn the Schlenk line stopcock to the closed position (parallel to tabletop) and then slowly turn it to the open position to the nitrogen manifold.
(iv) Watch the bubbler; when the valve is opened, the bubbling will cease or its bubbling rate will decrease while the nitrogen fills the evacuated hose up to your side-arm valve. The bubbling should return to its normal rate within a few seconds. At this point the hose is under a nitrogen atmosphere at atmospheric pressure.
(v) Now slowly open the side-arm valve slightly until the rate of bubbling decreases (or ceases). Going slowly will also make sure you do not disrupt the contents of the glassware (specifically if the contents are dry solids that can swirl up in the nitrogen gas stream entering the flask and potentially go up into the septum or other inconvenient places in the glassware). If you notice the oil is being sucked back up the bubbler, quickly close the valve as there is insufficient nitrogen flow. Partially close the bubbler valve to increase the flow/pressure of nitrogen and then open the side-arm valve as before. Wait until the bubbling returns to its normal level.
(vi) Close the valve to the side-arm glassware (once the bubbler has returned to its normal bubble rate the system is at atmospheric pressure and there is no need to ait any longer before proceeding to the next step).
(vii) Turn the valve of the Schlenk line to the closed position and then turn it to the vacuum position, slowly.
(viii) Slowly open the valve to the side-arm so as not to disrupt the contents of the glassware (specifically if you have a solution, as bumping can occur). Open it only partially and wait to ensure the contents of the glassware are not disrupted. After about 5-10 seconds you can open the valve fully if no disruption is observed. Leave the glassware open to vacuum for 3-10 minutes (3 minutes for smaller glassware through to 10 minutes for larger glassware). Leaving it longer (ideally 15 minutes) is not a bad thing but these times will make it reasonable for one to perform a reaction in a reasonable amount of time available to most undergraduates.
(ix) Repeat steps (ii) through (viii) at a minimum of TWO more times, ideally FOUR more times.
(x) Finish the cycle procedure by returning the side-arm glassware to nitrogen atmosphere by repeating steps (ii) through (v). The system is now air-free!
Video Here
2. "Air-Free" solution transfers: this technique is used very frequently to add solvent and/or reagent solutions into reaction flasks. One could concieve of using syringes to tranfer solutions but in general, syringes are not used in the Daley lab, except at time for reagents that are liquids at room temperature, when small amounts of solvent are required, or if very precise amounts are required. The method used in the Daley lab is the "Cannula Transfer" method, where stainless steel cannula (essentially metal tubes) are connected between flasks and the solution is PUSHED through the cannula from one flask to the other. To push the solution through, we have a higher pressure of the inert gas in the glassware that contains the solution to be transfered relative to the flask receiving the solution. We DO NOT PULL/SUCK the solution through the cannula by using vacuum on the receiving flask to pull the solution through the cannula from the transfer flask. The reason is simply that one has far less fine-tune control over the rate, etc. of flow of the solution using vacuum whereas one can rather easily control the flow rate, etc. by fine-tuning the inert gas pressure from the Schlenk line using the bubbler controller. Below is the protocol for performing simple solution transfers.
Qualitative Solution Transfers (exact volume is not critical):
(i) Get a double-deflected point (i.e. sharp ends), appropriate sized cannula (length and diameter) that has been in the oven overnight. For large solution volume transfers use larger diameter cannula (smaller gauge; typically 18 gauge for greater than 10 mL; 16 gauge should be considered if >250 mL of solution is to be transfered - specially if quick addition is desired). For smaller solution volumes use smaller diameter cannula (larger gauge; 20 gauge typically; 22 gauge is usually only used for transfer to very narrow tubes like NMR tubes).
(ii) Increase the pressure of inert gas flowing to the transfer flask by increasing the flow rate of the bubbler. To do this, one partially closes the bubbler to the atmosphere by turning the valve on the bubbler (top) clockwise. IMPORTANT - NEVER SEAL THE BUBBLER COMPLETEY! The bubbler must always be bubbling, if you close the valve completely you cannot gauge the pressure of the inert gas in the Schlenk line, which could become dangerously high and cause the Schlenk line stopcocks to fly out of their ports or even potentially have the Schlenk line manifold explode! Increase the rate to about 4-5 bubbles per second to start. You may be required to increase it if the solution does not transfer but start low and then slowly increase to decrease any risk of accident/injury.
(iii) Put one end of the cannula into the transfer flask (but not into the solution) and let the gas flush through the cannula for 15-30 seconds to remove oxygen from the tube.
(iv) Put the other end of the cannula into the receiving flask.
(v) Close the receiving flask to the Schlenk line (e.g. if side-arm flask - close the stopcock on the side-arm; if round bottom flask with needle to Schlenk line - close the stopcock directly on Schlenk line). This isolates the receiving flask and allows one to more easily manipulate its pressure.
(vi) Put an "Exit Needle" into the receiving flask septum. An "Exit Needle" is defined as a disposable needle. The needle diameter size (gauge) should be chosen such that it is smaller than the cannula used to connect the flasks (usually 2 gauge larger: e.g. 18 gauge cannula - use 20 gauge Exit Needle). Now the receiving flask remains under air-free conditions by the continuous flow of inert gas coming through the cannula attached to the transfer flask yet the excess pressure is allowed to escape through the Exit Needle.
(vii) Push the end of the cannula in the transfer flask into the solution, below the surface of the solution, and wait 10-20 seconds. If the solution does not begin to transfer, it is likely you will need to increase the flow-rate of the inert gas by further closing the bubbler (but again - DO NOT COMPLETELY CLOSE OFF THE BUBBLER. Make only small changes to the flow rate at one time and be sure to wait 20-30 seconds after adjusting the rate to see the result. The pressure builds up slowly so if you do not wait enough time after adjusting the flow rate, the system may not have reached its equilibrium pressure and you could potentially over-pressurized the line/flasks. So be careful!
(viii) Once the amount of solution desired has been transfered, pull the cannula out of the remaining solution in the transfer flask.
(ix) Remove the Exit Needle from the receiving flask.
(x) Open the recieing flask to the inert gas from the Schlenk line.
(xi) Remove the cannula from the flasks.
Quantitative Solution Transfers (complete solution volume transfer is critical):
(i) Get a single-deflected point / blunt end (i.e. sharp ended and blunt ended), appropriate sized cannula (length and diameter) that has been in the oven overnight. For large solution volume transfers use larger diameter cannula (smaller gauge; typically 18 gauge for greater than 10 mL). For smaller solution volumes use smaller diameter cannula (larger gauge; 20 gauge typically; 22 gauge is usually only used for transfer to very narrow tubes like NMR tubes).
(ii) Increase the pressure of inert gas flowing to the transfer flask by increasing the flow rate of the bubbler. To do this, one partially closes the bubbler to the atmosphere by turning the valve on the bubbler (top) clockwise. IMPORTANT - NEVER SEAL THE BUBBLER COMPLETEY! The bubbler must always be bubbling, if you close the valve completely you cannot gauge the pressure of the inert gas in the Schlenk line, which could become dangerously high and cause the Schlenk line stopcocks to fly out of their ports or even potentially have the Schlenk line manifold explode! Increase the rate to about 4-5 bubbles per second to start. You may be required to increase it if the solution does not transfer but start low and then slowly increase to decrease any risk of accident/injury.
(iii) Put one blunt end of the cannula into the transfer flask (but not into the solution) and let the gas flush through the cannula for 15-30 seconds to remove oxygen from the tube.If there are not holes in the septum to the flask you will first need to use the deflected/sharp end to puncture the septum and then put the blunt end through the newly made hole.
(iv) Put the other, deflected-end, of the cannula into the receiving flask.
(v) Close the receiving flask to the Schlenk line (e.g. if side-arm flask - close the stopcock on the side-arm; if round bottom flask with needle to Schlenk line - close the stopcock directly on Schlenk line). This isolates the receiving flask and allows one to more easily manipulate its pressure.
(vi) Put an "Exit Needle" into the receiving flask septum. An "Exit Needle" is defined as a disposable needle. The needle diameter size (gauge) should be chosen such that it is smaller than the cannula used to connect the flasks (usually 2 gauge larger: e.g. 18 gauge cannula - use 20 gauge Exit Needle). Now the receiving flask remains under air-free conditions by the continuous flow of inert gas coming through the cannula attached to the transfer flask yet the excess pressure is allowed to escape through the Exit Needle.
(vii) Push the blunt end of the cannula in the transfer flask to the bottom of the flask, below the solution, and wait 10-20 seconds. If the solution does not begin to transfer, it is likely you will need to increase the flow-rate of the inert gas by further closing the bubbler (but again - DO NOT COMPLETELY CLOSE OFF THE BUBBLER. Make only small changes to the flow rate at one time and be sure to wait 20-30 seconds after adjusting the rate to see the result. The pressure builds up slowly so if you do not wait enough time after adjusting the flow rate, the system may not have reached its equilibrium pressure and you could potentially over-pressurized the line/flasks. So be careful!
(viii) Wait until all the solution transfers over. You may have to more the blunt-end of the cannula around the flask to get the last reminants of the solution.
(ix) For best results, transfer a small quatity of solvent used for reaction (same solvent used in transfer flask) to the transfer flask via cannula from a third flask that has only fresh solvent in it (see Qualitative Solution Transfers protocol above).
(x) Stir the solvent in the transfer flask, or simply swirl the flask, to wash the sides of the flask to get any leftover reagent into the solution.
(xi) Transfer the wash solution into the receiving flask as before (steps (vii) and (viii)).
(xii) Repeat steps (ix) through (xi) two more times.
(xiii) Remove the Exit Needle from the receiving flask.
(xiv) Open the recieing flask to the inert gas from the Schlenk line.
(xv) Remove the cannula from the flasks.
3. Solvent evaporation: this technique is used very frequently to strip of the solvent from a reaction mixture or a filtrate solution, as examples. The method is very straight-forward with the main key being the correct setup of the glassware, traps, etc. As such, the setup is pictured, labeled, below for one's reference.
(i) Get a double-deflected point (i.e. sharp ends), appropriate sized cannula (length and diameter) that has been in the oven overnight. For large solution volume transfers use larger diameter cannula (smaller gauge; typically 18 gauge for greater than 10 mL;