kemikallyimbalanced
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Vac Distillation Problem
When I'm vac distilling it's very hard for me to change flasks. What is the best way to do this? The flasks only come off with great effort even when
the vac is off. This might be cause by setting up the glass at an imporper angle but I'm not sure. Is it even ok to shut the vac off and on with all
the glass still connected?
[Edited on 31-3-2007 by kemikallyimbalanced]
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chemrox
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In order to change flasks you must release the vacuum. You should have a trap in the system consisting of a sidearm flask with a two hole stopper and
glass tubes. The sidearm goes to the vacuum and the longer tube goes to the glassware. The shorter tube should have a short rubber hose with a
clamp on it. This is where the vacuum is released.
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evil_lurker
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Or if your working with small amounts buy a "cow" type reciever... then all you have to do is rotate it to cut your fractions.
If your working with larger amounts, you need a "perkin triangle" which will let you change out recievers by releasing vacuum on them yet keeping
vaccum steady in the system.
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kemikallyimbalanced
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That perkin triangle looks like some hardcore shit and I bet it costs a ton. I remember reading in Zubricks manual that he had some way of removing
flasks easily during vacum distillation but I cant recall what he said. I do have a custom made trap but I may have it set up wrong. Chemrox could you
put up a diagram of this setup or have a link to one? Thanks
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chemrox
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diagram
I can't do it where I am right now but tomorrow I can make a crude jpg of it or shoot a picture of mine. Meanwhile please see if the Organic Chem
Lab Survival manual has been posted in references .. it probably has a good diagram of the setup.
I like the cow idea but I haven't had the bucks to buy one and haven't found one on ebay or LabEx (but I haven't lookedf recently either.)
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chemrox
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Please bear in mind this is not an ideal solution. You interrupt the distillation and when you resume it you have to restore the vacuum and heat. A
Perkin set up would be ideal .. a cow is good too, if as the man says, the quantities are appropriate.
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bio2
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To change receivers without any added components simply
shut off the heat, slowly bleed off the vacuum then quickly
change receiver flask then slowly reapply the vacuum over
a couple of minutes until it is near the same as before then
reapply the heat and proceed to collect the next fraction.
Watch carefully for bumping when the vacuum is reapplied
and use the stirring speed to control the boil-up rate.
You may also have to wait a few minutes when the heat
is turned off to prevent superheating hence the slow
re-application of the heat.
It works well enough once you get the hang of it.
[Edited on by bio2]
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chemrox
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Yes but he needs a trap in the line from the flask to the pump; for several reasons .. including being able to bleed off the vacuum.
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