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:

filtration
solvent removal
rotary evaporation
vacuum distillation

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 disposal 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.)

Click on the thumbnail for a larger picture of the vacuum system. 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.

Procedure

Connect to the vacuum system 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 the switch is on.)

Open the vacuum outlet. There 3 several types of outlets; two types you turn counterclockwise to open, one you turn the lever to the vertical position. Check the pictures for details.
Be careful that you do not over-turn an outlet. If over-turned, they can be ruined.

You should hear the vacuum hiss.

If you do not have good vacuum at your outlet, check first that the pump is on. Then, check the other 7 outlets on your system: if they are all open and either in use or just open and not being used, 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.

Water Aspirators

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

They waste water, since you have to run the water at full blast to create a good vacuum.
Volatile solvents are carried out from your flask and through the aspirator to the water that is running down the sink - this means you are contaminating the waste water with organic solvents.
Aspirators often back water up into your glassware, whether it is a filtering flask or an evaporating flask.

However, all that said, often the mechanical vacuum system just doesn't provide enough vacuum if all 8 students are using it at one time and using it for vacuum filtration (as opposed to solvent removal) and/or leaving a vacuum outlet open or 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, if:

you are filtering a solution employing a non-volatile solvent (e.g., water)
you use a water trap if you are using the water aspirator for solvent removal, and the solvent is non-volatile

Procedure

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.
Only use this set-up if your solvent is non-volatile/non-hazardous. If your solvent is something like methylene chloride, it will be drawn out of the flask and end up in the water being flushed down the drain through the water aspirator. This is not good for the Boulder water treatment system.

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.
Only use this set-up if your solvent is non-volatile, such as water.

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Connect to the vacuum system 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 the switch is on.)
Open the vacuum outlet. There 3 several types of outlets; two types you turn counterclockwise to open, one you turn the lever to the vertical position. Check the pictures for details. Be careful that you do not over-turn an outlet. If over-turned, they can be ruined.
You should hear the vacuum hiss.
If you do not have good vacuum at your outlet, check first that the pump is on. Then, check the other 7 outlets on your system: if they are all open and either in use or just open and not being used, 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.

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. Only use this set-up if your solvent is non-volatile/non-hazardous. If your solvent is something like methylene chloride, it will be drawn out of the flask and end up in the water being flushed down the drain through the water aspirator. This is not good for the Boulder water treatment system.
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. Only use this set-up if your solvent is non-volatile, such as water.