Flask Logo Organic Chemistry at CU Boulder

Vacuum Systems

The Organic Chemistry Teaching Labs are equipped with mechanical vacuum systems. A vacuum system produces a source of reduced pressure which is useful in many organic chemistry applications. In the teaching labs, the vacuum system is used for vacuum filtration, solvent removal, rotary evaporation, and vacuum distillations.

The vacuum systems we use are environmentally friendly, since the solvent vapors are trapped and collected. The mechanical diaphragm pumps are oil-free, eliminating the need to dispose of used, contaminated pump oil. Use of the vacuum systems precludes the use of water aspirators, reducing drastically the amount of water we use and preventing any contamination of waste water. The pumps are designed for chemistry applications: all parts that come into contact with chemicals are made of chemically resistant plastic materials. (For more information about these pumps, visit the VacuuBrand web site.)

The pump and condenser are shown above. We have two such systems in each lab room, which accommodate 16 of the 20 possible students. If your workspace does not have a vacuum system outlet, you will either have to use the water aspirator as a vacuum source or move to an unused vacuum system outlet when you need it.

To use the vacuum system, connect your glassware to the outlet with vacuum tubing. Make sure that the vacuum system is on: check with your TA, or see if the pump at your bench section is plugged in and switched on. You should hear the vacuum hiss. If you do not have good vacuum at your outlet, check the other 7 outlets on your system: if they are all open, your vacuum will not work very well. When you are done, turn off the vacuum outlet, then disconnect the tubing. Do not leave your outlet open when not in use.
There are several types of outlets in use. If you have one with a lever, then turn the lever to the vertical position to open it. The knob should already be open and you should not have to adjust it.
If you have an outlet without a lever, turn it counterclockwise to open it. Be careful that you do not over-turn an outlet. If over-turned, they can be ruined. There is a tiny pin inside which can get off track, making it impossible to open or close the outlet and causing the outlet to leak.

Water Aspirators

Water aspirators also provide a source of vacuum. While convenient, the use of water aspirators is discouraged for several reasons:

However, the mechanical vacuum system just doesn't provide enough vacuum if all 8 students are using it or if an outlet is damaged. During lab, things get busy and hectic, and the TA just doesn't have time to figure out who is wasting vacuum or what is broken. Therefore, you can use the water aspirators, as long as you are filtering a solution employing a non-volatile solvent (e.g., water) and you use a water trap.

This is where the water aspirator is located. Connect to the water aspirator with a piece of vacuum tubing, not Tygon tubing. To turn the water aspirator on, turn the faucet on full-blast.
This picture shows a water-trap placed before the flask, which is set up for a solvent-removal procedure. The water trap prevents water from the aspirator from being sucked into the solvent-removal flask - instead, if water is sucked into the system, it goes into the water trap.
The picture to the right shows a set-up for vacuum filtration. It can be used only if you are collecting the crystals and do not need the filtrate, since without a trap, you risk having water sucked into the side-arm flask.