UnintentionalChaos
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Bad chemistry in Pentryl Prep
While I have never before, to my knowledge, contributed to this subforum, I'd like to take a moment and point out a significant error in the
"published" prep of pentryl by user Axt.
The prep is available here: http://www.sciencemadness.org/member_publications/pentryl.pd...
While I could point out some more minor issues, I'd like to draw attention specifically to the preparation of N-(2-hydroxyethyl)-2,4-dinitroaniline
(Referred to in the writeup as 2,4-dinitrophenylaminoethanol).
Axt uses equimolar amounts of 2,4-dinitrochlorobenzene and "2-aminoethanol." The latter was "purified" by boiling this product: http://tinyurl.com/n3k398g until it reached the boiling point of the desired component. The component "Polyoxyethylene lauryl ether" would be far
less volatile than the 2-aminoethanol due to it's vastly higher molecular weight.
Also, there is a complete disregard for the volatility with steam (different from azeotrope) that is highly likely with 2-aminoethanol. Without
fractional distillation, you simply boil away a fair bit of the desired product with the water.
As the "purified" 2-aminoethanol surely had all of the original Polyoxyethylene lauryl ether present, and Axt used a quantity appropriate for
high-purity 2-aminoethanol, it is no wonder that yield was disappointing and a significant amount of (supposedly)
N,N-bis-(2,4-dinitrophenyl)-2-hydroxyethylamine resulted. Way more than a 1:1 ratio of 2,4-dinitrochlorobenzene to 2-aminoethanol was used. Ideally,
an excess of 2-aminoethanol would be used to discourage formation of N,N-bis-(2,4-dinitrophenyl)-2-hydroxyethylamine in favor of the desired product.
[Edited on 6-17-14 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Bert
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Mood: " I think we are all going to die. I think that love is an illusion. We are flawed, my darling".
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As far as the OTC sourcing of the monoethanolamine, I had wondered about the choice to distill this from the BBQ cleaning mixture- In USA at least,
it's freely sold as a pure(ish) technical chemical to hobbyist PC board makers.
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2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
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Rosco Bodine
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A little less than perfect, bad process chemistry now and then is inevitable from a bad bad bad bad boy  even if he isn't Australian. We all have our brain fart moments where we aren't 100%, and hope to survive to live and
learn. There is plenty of examples of error in the authoritative, peer reviewed literature, so there is a plenty enough of bad chemistry or minor
imperfection error to go around. All anyone has to do is be paying attention and look for it.
Keep a red marker handy. Then rely more on your corrected version of what is true. That could be good for a lot more things than just chemistry.
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dimroth
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Since I've conducted before mentioned reaction of 2,4-dinitrochlorobenzene with ethanolamine following the procedure of Axt couple of days ago, I may
have something to add.
Ethanolamine that I used was lab grade but nevertheless I had to purify it by simple distillation since it was old and brown colored. It however, did
not distill exactly at 170°C but came at the broad range of about 150-170°C. It was slightly yellow, later fractions were leaning toward
orange-brown (which distilled at about 170°C). I haven’t found that ethanolamine forms azeotrope with water and during distillation there was no
sharp rise in temp. but just steady rise. The amount of reagents for synthesis of N-(2-hydroxyethyl)-2,4-dinitroaniline were exactly as Axt used.
Results were similar. I obtained 17,66 g (55%) of product and 4,39 g of “bis” byproduct. There are 0,01116 mol of bis compound and I used 0,1402
mol od dinitrochlorobenzene which leaves 0,1290 mol for actual product. Regarding the actual amount of DNCB (0,1290 mol) that reacted with
ethanolamine, I then get 60% yield. In the next trials I will surely add an excess of ethanolamine so as to get minimum amount of byproduct. But as
you can see even if one uses much purer ethanolamine there’s still not a significant difference regarding the yield. OTC version using BBQ cleaner
ethanolamine stays a viable option, for sure.
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