Nickdul
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Facile, Efficient nitration of Phenol to 2,4-dinitrophenol
Hi all,
I recently came upon the following paper (attached):
Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 10, pp. 1577−1580
"Synthesis of 2,4-Dinitrophenol"
DOI: 10.1134/S1070427212100163
Abstract—New highly selective method is suggested for synthesis of 2,4-dinitrophenol by nitration of phenol with nitric acid in an aqueous-alcoholic
medium at the boiling point of the reaction mixture. The yield of 2,4-dinitrophenol is as high as 80%.
EXPERIMENTAL
We used for synthesis freshly distilled crystalline
phenol, concentrated nitric acid of chemically pure grade
(concentration 65%), and rectified ethanol (ethanol
content 95.3%).
2,4-Dinitrophenol. A 2.5-g portion of phenol and
an aqueous-ethanolic solution of nitric acid, prepared
from 12.5 mL of concentrated nitric acid and 50 mL of
ethanol, was mixed in a round-bottomed flask.
The reaction mixture was heated in an installation
with a reflux for 0.5–2 h. Then, approximately 50 mL
of a liquid was obtained by vacuum distillation. The
residue was transferred to a cup. The product crystallized
as yellow crystals. The crystals were washed with cold
water and dried in a vacuum-desiccator.
Yield: 4.7-8 g (>95%)
Disregarding the "transferred to a cup" nonsense, the procedure seems straightforward and as soon as I get back to my lab, I'd try to do it (with the
overarching goal of salicylic acid - phenol - 2,4-DNP - 2,4-diaminophenol HCL).
Until then, if someone could come up with a precedent synthesis or mechanism (EtNO3, nitronium ion? seems too little acid)
Thanks, looking forward to ideas 
Attachment: khabarov2012.pdf (175kB)
This file has been downloaded 830 times
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mnick12
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Uhhhhhh, there must be something wrong here or the article is complete bs.
Using a mixture of ethanol and nitric acid as a nitrating mixture, especially with heating, seems like a great way to have a nice lab fire/explosion.
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careysub
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That's what the paper claims. Does look like dubious reaction conditions - maybe you do get your product if explosion does not result? And the
experimental is awfully sketchy for what is supposed to be the sole breakthrough of their paper. Nothing on nitric oxide evolution, safety
considerations, variations, etc. It even makes it seem like you might be keeping nitric acid-ethanol mixture on hand.
Oh yeah, check out this YouTube video:
https://www.youtube.com/watch?v=uFwiZYfEsuY
This is 2 mL ethanol/4 mL conc. nitric acid simply added together and look at what happens at about 2:30.
If instead of adding 2 mL of ethanol they had added 15 mL, they would have had the recommended nitration mixture from this paper (but only 1/3 that
described in the experimental). Think about how you would like to try refluxing that for a few hours.
[Edited on 7-12-2015 by careysub]
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AvBaeyer
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I have to agree with Careysub. This paper is very suspect. I sure would not try it.
AvB
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macckone
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Given the 65% nitric and the large amount of ethanol, this is probably not going to explode. Given the large amount of ethanol, a runaway is equally
unlikely. One thing to keep in mind is that countries differ in regard to safety. Russia tends to shrug off safety concerns. Now back to the
reaction, at the end point there should be most of the ethanol evaporated off with about a 50:50 mix of water and product. This is the most likely
point for an accident as you have a heated solution of dinitrophenol. I would guess a water bath is used. And the ethanol should evaporate off with
most of the water remaining. It is an interesting reaction if it works. I would guess it actually does and the primary danger is overheating the
dinitrophenol if a water bath is not used. The transfer to a cup would be to encourage evaporation, ie. An evaporating dish. This compound is
reasonably safe when wet but dangerous when dry. Don't overheat or heat to dryness.
Ps. The concentration of nitric acid is 16% of solution with the added water, it should be less dangerous than 10% nital.
[Edited on 7-12-2015 by macckone]
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Nickdul
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Heh, I've known not to heat nitric acid and ethanol, and I did see that youtube video once I recognized it is a safety hazard.
I tried to find the Russian original of the paper and compare it to the translation, but the closest I found was that the authors submitted a patent
(attached). Thе procedure is the same, although it is unclear whether they only strip the ethanol/acid mixture by vacuum distillation, or if they
also distill the 2,4-dinitrophenol over. Funny thing, they outline a bunch other synthetic routes and find faults in them, so if they are to be
believed, their method is the best
[Edited on 7-12-2015 by Nickdul]
Attachment: RU2488575C1.pdf (340kB)
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[Edited on 7-12-2015 by Nickdul]
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Boffis
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Actually, when you think about the proposed method it's not as bad as if sounds initially. This is probably a nitrosation-oxidation process and these
are well established as a means of nitrating phenols. In essence the partial reduction of some of the nitric acid to lower N oxides brings about
nitrosation to 2,4 dinitrosophenol which is then oxidized by the excess nitric acid to the nitro compound.
[Edited on 7-12-2015 by Boffis]
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Nickdul
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Boffis, thanks for chiming in on this. Indeed, I have seen several preparative methods involving a nitroso- intermediate. Also, a "conventional" mixed
acid nitration synthesis from a Russian synthetic manual claims 65% yield after purification (acid-base recrystallization)
see attached
[Edited on 8-12-2015 by Nickdul]
Attachment: GolodnPraktOrgKhim_1976_p376.pdf (58kB)
This file has been downloaded 679 times
[Edited on 8-12-2015 by Nickdul]
Attachment: US3933926.pdf (685kB)
This file has been downloaded 637 times
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CuReUS
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I can't comment on the mechanism in the russian paper,but see this paper, they claim a 98% yield
https://www.thieme-connect.com/products/ejournals/abstract/1...
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Nickdul
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Zolfigol, M. A., Madrakian, E., & Ghaemi, E. (2003). Trichloroisocyanuric Acid/NaNO 2 /wet SiO 2 as an Efficient System for the Selective
Dinitration of Phenols under Solvent-free Conditions. Synlett, (14), 2222–2224. http://doi.org/10.1055/s-2003-42063
Another one on my list then
Attachment: s-2003-42063.pdf (42kB)
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Fantasma4500
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so the article suggests lower than actual 65% HNO3 to be used? i have long ago succesfully made benzyl nitrite using catalytic amount of NaNO2 along
with 5% HNO3 and benzyl alcohol, the benzyl nitrate broke down forming benzaldehyde. the alcohol could be playing a role in forming NOx which would
then efficiently react with the phenol, the TCCA + NaNO2 i'd say suggests that there is something about NOx being useful for making DNP
of what i find its suggested that DNP is a "powerful explosive", relative to TNP how much would that be? it leaves 3 carbon atoms after complete
decomposition, 80% yield is quite great for something that doesnt even require sulfuric acid and has doable stability
what im more interested in is - what are the alkali salts like? sodium picrate is a weak primary, so what about diphenolates? with such great yields i
think were missing out on some very potent compounds
maybe the heavymetal diphenolates would be interesting, and if this all turns out mundane maybe DNP would serve as high yield precursor for TNP?
phenol is as easy as salicylic acid destructively distilled, and possibly this can be catalyzed with an mixture of copper salts
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Chemi Pharma
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All these papers @Nickdul brought to the thread have been already discussed here at the 2,4 DNP thread. See: http://www.sciencemadness.org/talk/viewthread.php?tid=15006&...
The same concern expressed here about mixing ethanol and 65% HNO3, were discussed at that thread. Something needed to think about is the fact the
presence of phenol in the reaction mix as a substrate will atenuate every possible runway. The NOx will react in situ with phenol and we will not see
the large brown fumes of NO2 escaping from the vessel as we can see in the you tube video @careysub indicated to us, but just ethanol, water and a
little NO2 vapors evoluting instead.
Nobody here didn't ever try to make mercury fulminate from mercury as substrate, 95% ethanol and 65% nitric acid? I did. Several times. It's the same
thing. No runaway at all, just a mild reaction, even heating the mix to kick off .
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Melgar
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You should theoretically be able to use n-butanol instead of ethanol, which seems like it'd be a lot safer. The problem with ethanol is that it's
oxidized into acetaldehyde, which can undergo a haloform-like reaction with nitrous acid (which forms after nitric acid oxidizes something). Since
the runaway only seems to occur with alpha-methyl carbonyl groups (similar to the haloform reaction) you should theoretically be able to avoid it by
using a longer-chain alcohol that isn't oxidized into an alpha-methyl carbonyl compound.
This is just a theory I've had, but woelen said something about similarities between hypochlorous and nitrous acids and it got me thinking about other
similarities.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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ChireadanPL
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Sorry for digging such an old thread, but I did this synthesis out of pure curiosity, and maybe somebody will be interested.
I used the method covered in "Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 10, pp. 1577−1580
"Synthesis of 2,4-Dinitrophenol", with some minor changes. Because in my amateur setting i do not have reflux or vacuum distillation setup for such a
small scale (i have it only for 1dm3 round bottomed flask), adn I certainly didn't want to mulltiply the scale of unknown and potentially explosive
reaction i did some modifications.
Reagents used were:
Ethanol 96%, pure p.a.
Nitric acid 65%, pure p.a.
Phenol, pure (99% assay min)
Sodium hydroxide, pure p.a.
Hydrochloric acid, pure p.a.
50ml of ethanol and stir bar were put into 250ml erlenmeyer flask with thermometer standing on magnetic stirrer. With vigorous stirring 12,5ml of 65%
HNO3 were added dropwise, as in preparation of ordinary nital for metallographic etching (I'm a metallurgist). This is slightly exothermic, smell of
acetaldehyde, and some white nitric oxides fumes arise. Solution was then cooled to room temperature. With continous VIGOROUS stirring 2,5g of
crystalline phenol were dumped in. As soon as the phenol dissolves, the solution becomes slightly pink-reddish. Since i do not have reflux condenser
for such a small flask i've installed a short glass tube wrapped with cloth soaked in cold water in top of the erlenmeyer flask to limit evaporation,
and turned on the heating. The mixture was heated with continuous stirring for about 20 minutes between 60 deg C and boiling point which is about 78
deg C (b.p. of ethanol). The solution becomes reddish brown, and strong aromatic smell is evident even under the fume hood. Since i could not vacuum
distill, glass tube was removed, and solution was evaporated. When there is about 25ml left in the flask some nitrogen dioxide comes off. When there
is about 15ml left solution rapidly separates into two phases, aequous and red oily layer at the bottom. Solution was then cooled in water bath, and
after cooling when the bottom of the flask is scratched with glass stirring rod, the red oily phase crystallizes. Contents were gravity filtered on G2
schott funnel, and washed with cold water yielding orange-red paste, the red color does not go away despite washing. Then, as in paper, 100ml of 1M
NaOH was prepared, and the paste was dumped to the NaOH solution. With heating and stirring the paste dissolves yielding very deep red-brown
solution, which looks like a very strong tea. Everything dissolves at about 65 deg C. Mixture was then cooled to about 30 degC, and hydrochloric acid
was added dropwise, which causes yellow crystals to crash out of the solution. This was vacuum filtered (with only very slight vacuum) on G3 schott
funnel, and washed with cold water.
Final product is about one and a half teaspoon of flaky yellow crystals which i believe to be 2,4-dinitrophenol. I did not weigh it, since I didn't
want to dry the potentially explosive compunds. Product is soluble in ethanol, giving strongly yellow solution, which stains very strongly.
I do not encourage anybody to try this method, as I do not know, if it can lead to explosion. Sorry for my very bad english.
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Tsjerk
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Nice write-up. I wouldn't worry too much about the explosive properties of the di-nitro compound as long as you keep it away from metals. Even the
tri-nitro is a secondary explosive when pure. But better save than sorry of course.
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