MG 1026 Schlenk Line Operation
Author: James M. McCormick
Last Update: February 20, 2009
Introduction
A schematic diagram of the Schlenk line in MG 1026 is shown in Fig. 1. At the present time it is not truly a Schlenk line because we have no pump attached to the vacuum manifold and we have no mercury bubbler. However, we can still use it to work under a nominally oxygen-free atmosphere by purging the nitrogen manifold, and anything attached to it via the stopcocks, with a stream of nitrogen gas from the cylinder.
Figure 1. Schematic diagram of the Schlenk line in MG 1026.
Operation
The keys to safe operation of a Schlenk line are 1) always know what the pressure is and never exceed the safe pressure limit, 2) never continue to admit gas to the system when you are not sure where the gas is going, 3) never have the flow rate so fast that mineral oil is blown out of a bubbler into the system or into the hood, and 4) use two hands to turn the glass stopcocks on the manifold.
The following assumes that you will be starting up the line when there is no nitrogen gas flow through the system.
1) Check that the stopcocks, the inlet control valve, the regulator needle valve and the tank valve are all closed. Do not tighten the inlet control needle valve or the regulator needle valve more than finger tight. Use two hands to close the stopcocks. If the stopcocks feel dry or are hard to turn, remove them and apply a light coating of high vacuum silicone grease. Reassemble the stopcocks and carefully turn several times to distribute the grease; repeat process as necessary being careful not to fill the stopcock inlets and outlet with grease. Do not grease any of the valves.
2) Open the tank valve. The needle on the tank pressure gauge should rise to indicate the pressure in the tank. If the tank does not have enough nitrogen for your experiment, please change the tank.
3) Verify that the outlet pressure gauge reads less than about 15 psi. This should have been set by the last user and not changed. However, it can be reset using the regulator pressure controller. IMPORTANT! Do not use the regulator pressure controller to adjust the flow through the system!
4) Open the regulator need valve. One to two turns should be sufficient.
5) Open the inlet control needle valve slowly and carefully to start flow through the system, which is indicated by bubbles of nitrogen in the inlet bubbler and bubbles of nitrogen escaping through the exhaust bubbler. A flow rate of about a bubble a second should be sufficient at this point. Use only the inlet control needle valve to change the flow of nitrogen through the manifold! IMPORTANT! If you see bubbles in the inlet bubbler, but none in the exhaust bubbler, immediately check for open stopcocks. If you see no open stopcocks, shut down the flow, carefully open a stopcock to vent the manifold and carefully check the system.
6) With a flow of about a bubble per second in the inlet and exhaust bubblers, purge the line with nitrogen. This will take about 20 min, or more. If you can’t wait that long, you can increase the flow rate as long as you don’t blow mineral oil out of either bubbler (persons doing this will have the chore of cleaning the manifold and will carry a shame that will be passed down even unto the seventh generation). If you turn the flow up, you must remember to turn it down.
7) Once the manifold is flushed you can open the appropriate stopcock to flush your system which will be attached to one of the ports on the manifold via red rubber vacuum tubing. There are several ways to do this.
•Attach the vacuum tubing to your system (via a gas inlet adapter), but leave the system open in some way so that you can blow nitrogen through the system. If you choose this method, you will need to increase the nitrogen flow, but remember to turn it down once you’ve closed the system.
•One could also attach a mineral oil bubbler, or a bubbler containing a different liquid, to the system (again using a gas inlet adapter) and just continue flowing nitrogen at a normal rate.
•Another way to purge your system is to attach a glass tube (or Pasteur pipette) to the hose and simply insert it into the system through an open port. This is a useful way to quickly to remove most of the air from your system. It takes about 10-20 min to remove most of the air (depending on your solvent), and reduces oxygen present in the solvent to a level that is low enough for most work, but it can evaporate a good deal of solvent.
8) When your system has been purged with nitrogen (this may take anywhere from a few minutes to 20 minutes), you can close it. Don’t forget to turn down the nitrogen flow immediately after you do this! As long as there is nitrogen flow through the manifold (bubbles at both the inlet and exhaust bubblers), your system will be under nitrogen. Note that as long as the exhaust bubbler is open to the air the system is not closed!
•If you will be connecting/disconnecting things from your system during the course of your experiment, turn up the nitrogen flow while making the change using the inlet control needle valve. Remember to turn down the flow again once you are finished making the change.
•If you will be heating your system under nitrogen, set the flow rate (1 or 2 bubbles per second is usually sufficient) before starting to heat and do not change the flow rate during reflux. Take care when refluxing that you do not blow your reaction up into the manifold. People who do this will share the same fate as those who blow mineral oil out of the bubblers.
9) When your experiment is finished, close the stopcock to your system (use two hands) and remove it from the line. If someone else will be using the line shortly after you, you can leave it with all the stopcocks closed and a nitrogen flow of 1 bubble per second. If nobody will be using the line, close (in order) the inlet control needle valve, the regulator needle valve and the tank valve. Remember to close the inlet control needle valve and the regulator needle valve no more than finger tight. Do not change the regulator pressure control valve.