evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
|
|
Separation of nitrotoluene isomers from crude nitration product.
I'm looking to nitrate some toluene to the ortho isomer.
Standard expected crude product distribution ratio calls for 60% ortho, 37% para, and 3% meta isomers.
What is the most effective means of separation?
From what frogfot has on his website, a preliminary crystallization of the crude product at 0ยบ, followed by fractional distillation under reducted
pressure of 50% of the crude product, followed by another fractional crystallization, so on and so forth.
Anyone have any specific information that might be useful?
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
There have been several threads on this already.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
The o-nitrotoluene is a liquod and so chilling the initial mixture to a few degrees above its mp will ppt most of the p-isomer and trivial qty of
m-isomer.
The fractionation under vacuum purifies the o-isomer. The trick is to do the fractionation carefully and properly and to stop when the temp at
stillhead indicates some p-isomer is starting to come over.
Then you start freezing out the p-isomer from what is left in the pot, adding the solid to the first recovery of -isomer. Usually only 2-3 such
procedures will be sufficient and then you can fractionate your crude o-isomer. Unite the two distillates and you should have pretty pure
o-nitrotoluene at about the yield you mentioned.
The crude p-nitrotoluene containing a little m-isomer can be recrystallized till it gives a lit. mp. It is not really worth trying to recover the
small amt of m-isomer from the mother liquor unless you are working on a larger scale.
CAUTION:
Your nitration should never be allowed to exceeed 30 C of you might have some dinitrotoluenes or even TNT in the product. In that case the
fractionation (especially if done at atmosphere) is HIGHLY dangerous and can explode. Try to stay under 25 C at all times. And do the fractionation in
vacuo as a precaution anyway.
|
|
|
vulture
Forum Gatekeeper
Posts: 3330
Registered: 25-5-2002
Location: France
Member Is Offline
Mood: No Mood
|
|
Enough threads on this one already. Closed.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
