UnintentionalChaos - 15-6-2014 at 20:29
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]
Bert - 15-6-2014 at 21:28
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.
Rosco Bodine - 16-6-2014 at 08:26
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.
<iframe sandbox width="640" height="360" src="//www.youtube.com/embed/aznod0Ij43g?rel=0" frameborder="0" allowfullscreen></iframe>
dimroth - 8-7-2014 at 02:36
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.