Class 3 Fractional Distillation Rules

1. Read all the rules on Class 1 distillations.

2. Do not confuse the condenser with the column. The column is wider, and has glass projections at the bottom to hold up the packing (see Figure 14).

3. Do not run water through the column jacket.

4. Occasionally, the column is used without any column packing.

5. Do not break off the projections that support the column packing.

6. If necessary, push a small wad of heavy metal wool (stainless steel, etc.) down to the bottom of the column to support small packing particles. Sometimes this wool is the entire packing.

7. Make sure that the packing will not fall into your distillation flask,

8. Lots of liquid will be held up on your packing, make sure that you have enough compound to start with, or it will all be lost in the packing.

9. Do not distill with too much liquid. Never fill the flask more than three fourths full.

10. For maximum yields, a chaser solvent should be used to push the compound that is left behind in the column on over into the condenser.

Special Note: Azeotropes

Certain liquids cannot be completely separated even by fractional distillation with the best equipment. These are the dreaded azeotropes, mixtures with a constant boiling point.

One common azeotrope is ethyl alcohol 96% water 4%. This combination can be boiled to dryness at one constant temperature. I cannot go into all the azeotropes you may run into during drug manufacture. So, before you attempt any formula, you must go to a science library and research all of the chemicals, solvents, reagents, etc., that are used in that particular formula and learn what can and cannot be used with what. Look in Chemical Abstracts, the Merck Index, or one of the many other fine reference books available.

For an example, let's say you want to chase some ethyl alcohol through your column packing. You notice that the boiling point of water is high enough to push or chase the lower boiling ethyl alcohol out of the column. Instead, they formed an azeotrope.

If an azeotrope boils off first, it is a minimum boiling azeotrope. The remaining liquids will not distill until all the azeotrope is gone. If the other liquids come over first, followed by the azeotrope, then you have a maximum boiling azeotrope.


1. There are two ways of generating steam for this distillation:

A. Leading steam directly into the system. This is a little more complicated and requires a water trap to keep excessive water from ruining the distillation (see Figure 15).

rubber tubing to connect glass tubing

Devices To Superheat Steam water / condenser rubber tubing to connect glass tubing water / condenser

Figure 15

to vacuum

Figure 15

B. Adding hot water to the distillation flask is also a simple way to generate steam also (see Figure 16).

extraction or separation funnel thermometer condenser



mantle — This is to make pressure or* hnt ^tw i

, <J equal in funnel plate ^ 4

Continue reading here: Figure

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