|Please note: (from top) use of clips to hold apparatus together, position of the thermometer, and the clamp holding the round bottom flask in place.||Please note: from left: use of clamp to hold collection flask, white tubing is where water goes in, red tubing is where water goes out.|
Distillation is probably the most common technique for purifying organic liquids. In simple distillation, a liquid is boiled and the vapors work through the apparatus until they reach the condenser where they are cooled and reliquify. Liquids are separated based upon their differences in boiling point. Two important things to note: 1) the tip of the thermometer must be correctly positioned slightly below the center of the condenser to accurately reflect the temperature of the vapors (see above left) and 2) the water supply should be connected to the lower port in the condenser and the drainage tube connected to the upper (in the picture on the right the right tube is connected to the water supply and the red tube is a drainage tube). Also be sure to use the thin-walled tubing and not the heavy walled vacuum tubing. Be very careful that your water lines do not come in direct contact with your hot plate, as the lines could melt resulting in a flood. Be sure to clamp both the round bottom boiling flask and the collection tube. Knocking over your collection tube at the end of the experiment if VERY frustrating. Below is a diagram of assembly: Generally, boiling stones will be added to the boiling flask to ensure even boiling. It is also wise to use some type of clamps to connect the various pieces of the distillation apparatus together. For low boiling liquids, enough heat may be provided simply by resting your flask on the hot plate (as shown above). You can also insulate your boiling flask and Claisen adaptor with aluminum foil. For higher boiling liquids it may be necessary to use an oil or sand bath to reach higher temperatures. The individual pieces of glassware needed for a simple distillation are diagrammed below.
Be sure to use the blue clips to attach the vacuum adaptor and
the Claisen tube and the distillation adaptor.
The setup for a fractional distillation is very similar to that for simple distillation. The only difference is the addition of a fractional distillation column, usually packed with some material of high surface area that produces a more efficient separation than the simple distillation. The same advice regarding the thermometer placement, clamping, and hook-up of the water tubes in the simple distillation also apply to the fractional distillation. As this apparatus is larger, practice additional caution to be sure that no glassware is broken or product loss. The choice whether to use the simple or the fractional setup will depend on the compounds that you are trying to separate. Obviously, the simple distillation setup is simpler and the distillation generally will be quicker than the fractional. However, the fractional setup is more efficient at separating liquids with fairly similar boiling points and at times is required.
|On the left, note that the tube
connected to the spigot is connected to the lower part of the
condenser, while the drainage tube is connected to the higher part. Also, note the position of the thermometer.
|Please note the use of clamps to secure the round bottom flask and the collection flask.|
Pictured on the left is the fractional distillation apparatus. A closer shot is on the right. Notice that the only difference between this apparatus and the simple distillation apparatus is that here, the fractional distillation column has been placed between the boiling flask and the distillation head. As in the simple distillation apparatus, not that the white tubing is connected to the water supply and the red tubing is the drainage tube. Also notice the position of the thermometer, blue clips, and clamps. A diagram of the apparatus is below.
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