evil_lurker - 27-4-2007 at 11:27
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 - 27-4-2007 at 12:06
There have been several threads on this already.
Sauron - 28-4-2007 at 00:50
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 - 28-4-2007 at 03:39
Enough threads on this one already. Closed.