constructive
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Distillation of Perchloroethylene
Hi sciencemadness! I am long time reader, first time poster. I learned a lot of stuff from this site, and i find it a real gold for a hobby chemists.
My chemistry knowledge is on the beginner level, so i try to read, read and read, try to find a answer my self [because a lot of it is probably
answered], and trying not to bother anyone if i am not in a such a big need.
This time i have a couple of questions, for you guys. Please if you know the answers help this baby buddy  .
I learned to distill a couple of weeks ago. I try it with H2O, then Acetone. Everything worked perfect, and i was VERY pleased about my new-learned
[and so useful] technique. With the distillation i will recycle used solvents, save money and save environment  ...
My apparatus is couple of RB flask's with distillation head [distillation curve or pipe], and 40mm liebig condenser.
With my chemistry experiements i use a Tetra/Perchloroethylene, so i need. to distill it to purify it. The only drawback is that i have around 150ml
and i guard it as a eyes in my head  .
Last night i try it to distill a 100ml of it. I assemble the apparatus, connected RBF [100ml] with distill. head, and connected head on the liebig
condenser. I don't have a grease, but i read numerous times before my distillation experiment, on the net and here, and got the conclusion that if you
distill on atmospheric pressure [without vacuum, + or - pressure] that generally you don't need the grease. Even if it need it, i don't have ANY
option to find it.
On the exit of liebigg is the flask to catch the distillate, in the ice bath. The water pump pumping the cold water through condenser, the RBF is in
the sand bath, and i started to raise the temperature on my stove.
Before the PCE started to boil i smelled it above the apparatus. I didn't worry too much, but when the distillate started to drop, i smelled the
distill head and i could smell the PCE.
I aborted the experiment, and started to think a little about the situation, and then i had 2 question on which i didn't had the answer. This are the
questions:
1) My apparatus has the ground glass joints which are connected and secured with zip-ties. I thought that i can walk away without grease, but i saw
that this is not the case. I used the PTFE tape on male joints, started to wrap upper part of it, then the joint itself, at an angle [to succeed to
not overlap the tape, and put the stress on the glass when it is hot, because PTFE tape when overlap can brake the glass when it is hot], but tape
wick the condensed tetra, upper from the joint on the glass. Can i wrap the ONE circle on the upper part of the ground glass joint, and with that
close the gap between the joints itself? Or do you have some better idea what to do?
2) Is it tetrachloroethylene so poisonous when hot or vapors of it? I can't stop thinking about it... I stopped the distillation as soon as i smelled
it, but i am afraid to start it again, even if i close the gap between joints... Is my fear justified or it is my paranoia?
Thanks everyone who help this self-learning, soon to be chemist ! And let the
force be with you! Thanks guys in advance...
P.S. sorry for my bad english it is not my native.
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MrHomeScientist
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It can be dangerous to use Teflon tape in ground glass joints, so I've heard numerous times. They make specially-made sleeves for joints, but those
are very expensive. I use DANCO Silicone Faucet Grease for my ground glass joints. Check your local hardware store. Just a couple dollars, and it will last me forever.
Grease should give you a better seal, too. Theoretically you should only need to grease the joints before the condenser (since everything should be
liquid after then), but I grease everything for security and easy of disassembly.
Having never heard of tetrachloroethylene before, I have no advice on that topic.
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Magpie
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By applying silicone grease to your joints you will eliminate most all of the fugitive vapors. But you may still smell some. I recommend you distill
outside or in a fume hood.
Here's information on tetrachloroethylene. I can buy this as a brake cleaner. I think it is also used for dry cleaning clothes.
https://en.wikipedia.org/wiki/Tetrachloroethylene
The single most important condition for a successful synthesis is good mixing - Nicodem
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Metacelsus
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Yes, definitely try to seal everything and use good ventilation. If you read the link Magpie posted, you'll see that PCE is not something you want to
be exposed to if you can help it.
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Praxichys
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Be careful where you use grease. I have found that perchloroethylene is great at dissolving Dow Corning high-vacuum grease. Only use a small amount
near the top of the joint (nearest to the outside). Press the joints together and rotate back and forth a few times to distribute the grease before
clamping.
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Magpie
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I routinely use Dow Corning's high vacuum grease - but you are right some reagents dissolve it. Dichloromethane, chloroform, and carbon tetrachloride
dissolve it, IIRC. One of my OC instructors would harangue his students not to use too much grease. But I've found that you do need to use enough so
that the joint will freely rotate. You can also see through the joint to see if you have good coverage.
For chlorinations I have been using Krytox grease (an ether). Yes, it is expensive but it only takes a little and it saves frustrating cleanups of
the joints due to chlorinated silicone white gunk. I don't know if it is soluble in the chlorinated solvents like silicone grease.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Praxichys
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Yes, I can confirm chloroform and dichloromethane dissolve it, as well as isopropyl nitrite.
The main problem is that you won't know there is a tiny amount of grease in the solvent until you go to dry some compound that has the solvent on it,
and it ends up a clumpy mess from the traces of re-concentrated grease. It may be better in some instances to leave everything downstream of the still
head to be made gas-tight by condensed liquid. Save the grease for sealing joints that are expected to be hotter than the BP of the solvent, since the
solvent vapors won't carry it.
Also, wow that Krytox is expensive. The best I can find is a half ounce (don't know if by weight or volume...) for $30. I guess as long as it was
saved for exotics, the price isn't terrible. I filled a 5ml syringe with the Dow Corning stuff for easy dispensing and it has taken me a year to
nearly finish it.
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Magpie
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Amazon has it for $15/0.5 oz:
http://www.amazon.com/DuPont-Krytox-Grease-Pure-Additives/dp...
The single most important condition for a successful synthesis is good mixing - Nicodem
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