Flash Evaporation to remove methylene chloride and

1
Flash Evaporation to remove methylene chloride and
Chemistry 227 Laboratory

• The recovery of the Aniline from Extraction.

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At this point, you should be able to account for
the following items.

• If you have all three of the above items,
• You are ready for the FLASH EVAPORATION.
• (p. 135-6 in Zubricks)

3
Start setting up with a good sturdy ring stand.

• If the rod is loose, tighten it before you begin
  so your set-up wont WOBBLE

4
Place the burneron the stand.

• Be sure your burner has a needle valve to adjust
  gas flow, and a rotating barrel to control
  air-flow.

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Now, add the iron ring

• Leave 2 to 3 inches for the flame.

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The wire gauzeis next.

• The wire gauze should have a ceramic center.
  Dont worry if there is hole in it.

7
A beaker serves as a hot water bath.

• Select a large beaker with sufficient capacity
• for your
• 50 mL RB flask.

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Clamp your 50 mL RB flask in the water bath

• Place the flask as far into the water as possible.

9
Attach the three-way adapter atop the flask.

• (The adapter is commonly called the still head.)

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CLAMP the condenser to anotherring stand.

• Do NOT trust a rubber band to hold that 60.00
  piece of glassware!

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Arrange an Erlen-meyer flask in an ice slurry
for your receiver.

• You may want to clamp the receive onto another
  ring stand.

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Attach water hoses to the condenser

• Water always
• enters from the LOWER end of the water jacket.

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Place the sep funnel on top of the still head.

• No need for a stopper but be sure the stopcock
  is CLOSED!

14
Remove the spent magnesium sulfate from the
aniline- in- methylene chloride solution.

• Wash with small portions of methylene chloride
  collecting all of the filtrate.

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Make sure the stopcock is CLOSED.(Dont be one
of those who will forget!)

• THEN, transfer the filtrate into the sep funnel.

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Now, light the burner and adjust to a good hot
flame.

• Bring the water in the beaker to near boiling.

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Then, adjust the burner to a smaller flame.

• The object is to keep the water bath hot.

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Open the stopcock SLIGHTLY and allow slow steady
drops to fall onto the hot flask.

• Methylene chloride (bp 40o) boils over (in a
  flash?) as the high boiling aniline (bp 185o)
  remains behind.

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To save some time, while the Flash Evaporation is
going on, you could filter the magnesium sulfate
from your p-dichlorobenzene and evaporate off
the methylene chloride.

• For this purpose, a number of small hot plates
  have been borrowed from the Frosh lab and are
  placed near your lab stations.

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Some are small, 4 x 4 inch hot plates, and some
are larger, and can accommodate several beakers.
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Finally, only aniline remains in the RB flask.

• Discard the methylene chloride in the receptacle
  provided for it -- and prepare to collect the
  aniline.

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Collecting the Aniline
Recovering the Aniline from Extraction.

• by distillation through an AIR-COOLED condenser.

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Turn off the burner flame.

• Remove the ice bath and receiver. Discard the
  methylene chloride in the receptacle provided.

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Drain the water from the water jacket.

• Remove the hoses from the condenser

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Remove the sep funnel from the still head.

• Loosen the blue retainng nut and return the sep
  funnel to the box from which you got it.

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You no longer need the water bath.

• Remove it and return the large beaker to the
  cabinet from which you got it.

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Lower the RB flask to sit firmly on the wire
gauze.LEAVE NO AIR SPACE!

• Lower the condenser assembly and re-attach it
  firmly to the still head.
• NO WATER HOSES!

28
Place the thermo-meter assembly into the still
head.

• The thermo-meter bulb should be just below the
  side- arm of the still head.

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Pre-weigh and label two DRY 50-mL Erlen-meyer
flasks.

• The first is to catch the forerun the second
  is to catch the final product (aniline).

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With a good, hot flame, distill the contents in
the RB flask.

• Switch receivers as the temper-ature climbs
  rapidly toward 180 degrees.

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Collect the aniline that boils at 180- 185
degrees.

• Never distill to a dry flask. When dark droplets
  spatter and char in the RB flask, you will have
  difficulty cleaning it!

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Part F- recovering the neutral compound

• Remove the spent MgSO4 by gravity filtration.

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UNDER THE HOOD, evaporate to near-dryness on a
hotplate.

• Cooling the residue should leave crude, solid
  p-dichlorobenzene.

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Transfer the residue into a larger RB flask, and
steam distill the mixture as before.

• Collect the distillate in an ice-cooled receiver.
• Recover the product on Buchner with suction.

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THIS CONCLUDES THE EXPERIMENT ON EXTRACTIONS

• Complete your laboratory report form, and prepare
  to turn in your two solid products. Keep the
  aniline.