Class 2 Vacuum Distillation Rules

1. Learn all the rules on Class 1 distillation.

2. The thermometer can be replaced with an inlet tube. If your flask has the provisions for both a thermometer and an inlet tube, then by all means also leave the thermometer in the reaction. The inlet tube should always be used to prevent the bad bumping that goes along with vacuum distillations. Boiling stones are useless.

3. Inlet tubes should have capillaries so small that the vacuum is not reduced. An inert gas like nitrogen should be introduced through the inlet tube if the compounds decompose in air.

4. Control of the heating is very important! After applying the vacuum, increase the heat very slowly.

5. Apply the vacuum before the heat. Never apply the vacuum to any hot substance. If you can apply enough vacuum to a liquid you can boil it without heat (a fact of physics),

6. During a vacuum distillation, it is not unusual to collect a pure compound over a 10-20° temperature range.

7. Try to keep your vacuum pressures equal. Buy or make a nano-meter to measure reduced pressure (see Figure 13).

8. A Claisen adapter can be added to allow use of both inlet tube and thermometer. If you must decide between the two then pick the inlet tube.

vacuum / adjusting vacuum / adjusting

Figure 13 and 14

Continue reading here: Class 3 Fractional Distillation Rules

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