Fery
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1,3,5-trinitrobenzene preparation from trinitrotoluene
I inherited a little of TNT which I believe was used in a granite quarry. As I'm not interested in explosives the only one usage was a preparation of
1,3,5-trinitrobenzene from it.
Searching sciencemadness forum I found these helpful threads/posts including also few pictures as trinitrobenzene easily deprotonates into red colored
compounds:
https://www.sciencemadness.org/whisper/viewthread.php?tid=29...
https://www.sciencemadness.org/whisper/viewthread.php?tid=26...
https://www.sciencemadness.org/whisper/viewthread.php?tid=14...
https://www.sciencemadness.org/whisper/viewthread.php?tid=26...
https://www.sciencemadness.org/whisper/viewthread.php?tid=73...
https://www.sciencemadness.org/whisper/viewthread.php?tid=18...
The trinitrobenzene could be used for charge-transfer complexes with electron-rich arenes, or reduced to 1,3,5-triaminobenzene (precursor to
phloroglucinol, but I have enough of phloroglucinol). Maybe it could be also used as an indicator for strong bases?
I followed the orgsyn method at 1/20 scale
http://www.orgsyn.org/demo.aspx?prep=CV1P0543
http://www.orgsyn.org/Content/pdfs/procedures/CV1P0543.pdf
Attachment: CV1P0541.pdf (299kB)
This file has been downloaded 207 times
http://www.orgsyn.org/demo.aspx?prep=CV1P0541
http://www.orgsyn.org/Content/pdfs/procedures/CV1P0541.pdf
Attachment: CV1P0543.pdf (299kB)
This file has been downloaded 170 times
18,2 g TNT was weighed (80 mmol), unknown purity, industrial origin, very old, very likely used in quarries.
27,0 g Na2Cr2O7.2H2O (90 mmol) purity 99,5%
H2SO4 96% pure 180 g (weighed it on scale, should be 98 ml, volume not measured)
18,2 g TNT was crushed into smaller pieces (read further how fine it should be crushed) and transferred into 250 ml FBF. Magnetic stirbar was
inserted, the flask was put into an empty bath from plastic dish and this was placed on magnetic stirrer. 180 g 96% H2SO4 was added, thermometer
inserted and magnetic stirring commenced. 6,5 g of Na2Cr2O7.2H2O from total 27,0 g was slowly added during first 10 minutes at which T raised from 15
to 25 C in t+10 minutes and later to 50 C in t+15 minutes. At that moment 10 C cold water was added into bath, T in reaction flask fall to 45 C at
t+18 minutes. As T should be kept at 45-55 C during whole oxidation process the water bath was quickly siphoned out. A little of dichromate added in
small circa 2 g portions during whole oxidation. When T raised to 55 C a little of cold water was added into bath but now only circa 1 cm high layer
in the bath (level of reactants in the flask circa 5 cm). T during reaction was kept at 45-55 C, when fall to 45 C, 2 g portion of dichromate added.
Addition of dichromate lasted 1,5 h and water had to be repeatedly added into and drained from bath, T always kept at 45-55 C. During second half of
the addition the mixture frothed a little (? impurities in TNT ?) and become thick, but powerful stirrer and medium size stirbar were able to continue
stirring.
After the addition of whole dichromate, warm water was added into bath and reaction continued stirring at 45-55 C (thermometer submersed into
reaction mixture) for 2 hours, during which the water in bath was repeatedly replaced with fresh warm water (alternatively aluminium or glass bath and
heating could be used too).
The reaction mixture was poured onto 200 g of snow (better than crushed ice due to much smaller particles, note that every overheating could
decarboxylate the trinitrobenzoic acid) while stirring with inserted thermometer, final T 20 C. A little more of snow added (circa 25 g) so the final
T 0 C.
Filtered on sinter. 20,6 g wet crude product obtained. Air dried. The product 1,3,5-trinitrobenzoic acid still not completely dry the next day,
weighed 17,8 g (there is no need to dry the crude product).
Circa 3 g of 2-3 mm pieces of TNT stayed in bottom of reaction flask - crushing TNT at the beginning into more fine particles is highly recommended.
It seems that crushing TNT into mixture of dust with also too big pieces circa 3 mm at the beginning was not enough and it had to be crushed to only
fine particles completely as these 3 mm pieces stayed unreacted (3 g of these pieces recovered from 18 g of reactant).
15 % NaOH solution was prepared by dissolving 4,0 g NaOH in 26 ml H2O and cooled down to 0 C.
Crude product (trinitrobenzoic acid) was partially dissolved in 100 ml water and warmed to 35 C. It was then neutralized with 15% NaOH solution at 35
C (thermometer inside) dropwise by pipette and stirring in cold water bath, circa 1/3 of the NaOH consumed when color changed to red, then immediately
2 drops of acetic acid added and color reverted back to yellow. The thermometer was submersed into the neutralized mixture during whole time as
overheating could decarboxylate the acid. Too low temperature is also undesirable as then the solubility of the acid is low.
The mixture was gravity filtered through filter paper into 250 ml FBF. 3,5 ml acetic acid added into the filtrate. Condenser attached and flask
carefully slowly heated (CO2 effervescence) and then refluxed for 3 hours.
Cooled in cold water bath while stirring by hand until product solidified. Gravity filtered on filter paper, air dried.
Crude 1,3,5-trinitrobenze product obtained in yield 7,3 g.
Product dissolved in 5,7 g acetic acid under reflux (yeah too much soluble in this solvent).
Cooled outside (winter 0 C temperature) at which also acetic acid crystallized so it was necessary to repeat the reflux and then cooled only to room
temperature 20 C.
Solubility seems to be approximately 30-40 g of trinitrobenzene in 100 g of acetic acid at 20 C.
Crystals vacuum filtered on sinter, washed with little of acetic acid, sucked to dryness. Air dried. The color of the product was not satisfactory (a
mixture of paler crystals with darker pieces).
Into the mother liquor was repeatedly (5x) added circa 1 ml of water at which substantial amount of impure trinitrobenzene recovered.
So maybe it could be recrystallized from diluted acetic acid but this was not tried. Solubility in diluted acetic acid should be lower and the diluted
acid (maybe 90, or 80, or 70% ???) should not crystallize at 0 C so cooling to lower temperatures could crystallize more of the product from the
solvent.
So far 5,0 g of trinitrobenzene obtained and some recovered from acetic acid mother liquor.
The 5,0 g trinitrobenzene was recrystallized from 40 g methanol (weight on scale, volume was not measured) - dissolved at reflux temperature, cooled
to 0 C outside (winter temperature), vacuum filtered on sinter at 0 C outside, washed with little of 0 C cold methanol on sinter, sucked to dryness.
Air dried for 2 days, second day the weight did not decrease anymore.
Yield 3,3 g.
m.p. 121,5-123 C (lit. 123.2 °C)
Recovered crop from acetic acid mother liquor was dissolved in methanol mother liquor and volume reduced to half by evaporation on hot plate. After
cooling down to 0 C, totally 2,4 g impure crop obtained which was recrystallized from 20 g methanol. 1,6 g trinitrotoluene obtained with somewhat
discoloration, but m.p. was still good, this crop seemed to be still pure enough (just a little discolored).
photos will follow soon
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Fery
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reactants
TNT + H2SO4, note the TNT had to be crushed to smaller pieces
  
the T during oxidation should be kept in 45-55 C using cooling water bath and the rate of addition of dichromate
  
the reaction at the end become thick and frothy, it was then poured onto snow
 
1,3,5 trinitrobenzoic acid precipitated and the mixture was then further cooled down to 0 C by addition of little of snow
  
the acidic solution was then filtered on sinter and washed with ice cold water to remove traces of Cr3+, note the Cr3+ is green and after washing it
out the washings become yellow perhaps due to trinitrobenzoic acid coloration, do not wash more than necessary, but wash out all Cr3+ (green color,
testing by precipitation with diluted cold NaOH solution, trinitrobenzoic acid reaction with cold solution of NaOH does not produce precipitate, at
elevated temperature it decomposes to almost white product unlike Cr3+) - I forgot to mention that in my initial post
100 ml of water was added to 1,3,5-trinitrobenzoic acid and heated to 35 C in warm water bath (do not overheat as then the acid decarboxylates, do not
let too cold as then the acid solubility is low), always keep inserted thermometer
the neutralization, 1 last drop of 15% NaOH is capable to change color to red, note do not add more than that last drop!!!, stir the mixture well
during whole time and cool down if necessary so the neutralization is performed at 35 C (low temp = low solubility of acid, high temp =
decarboxylation of the acid)
then quickly add 2 drops of acetic acid at which the color reverts back to yellow, leaving the previous red color for long time allegedly has bad
impact on the quality of the product
 
gravity filtered, only little captured on filter paper
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Fery
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decarboxylation under very weak reflux, then full reflux for 3 hours
after cooling down the 1,3,5 trinitrobenzene solidified and was filtered out, then air dried to the next day
 
crystallization from acetic acid
 
some impure product recovered from acetic acid mother liquor
crystallization of the main crop from methanol
  
impure product recovered from acetic acid mother liquor dissolved in methanol mother liquor, evaporated to half of its volume, crystallized on
cooling, filtered, then crystallization from 20 g of methanol, here the final crystallization from 20 g of methanol
comparison of main crop (pale yellow, left beaker on 1st and 2nd picture where photo taken against sunlight, right beaker on 3rd picture where photo
taken with sunlight from the back) and second crop (a little darker, but still good m.p.)
  
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Texium
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Very nice work! Be careful with that product though, as 1,3,5-trinitrobenzene is more explosive than TNT and can detonate from shock in solid
crystalline form like you have. Take care not to grind it or handle it roughly.
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Fery
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Hi Texium, thank you, I did not know that it is so much sensitive. I always thought that it requires primary initiator like Pb(N3)2 or Hg fulmitate to
detonate. Btw for crushing TNT I used common pliers from hand tools shop, as the TNT was in bigger pieces of few grams. But apparently I did not crush
TNT thoroughly enough. Very likely I had to sieve the crushed TNT through fine sieve (at most 1 mm) and crush again all pieces bigger than 1 mm.
Do you know any interesting usage of trinitrobenzene? I mean in chemistry (organic, analytic etc), not as an explosive. So far I saw only its
deprotonated form (that picture with red color during neutralization).
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Texium
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I don’t know. Besides reducing it to the corresponding triamino compound, which would give you some handles to work with, I don’t see it having
many synthetic uses. It’s so strongly deactivated that it would likely be completely inert towards electrophilic substitution. The fact that it is
easily deprotonated is interesting though. You may be able to use that to your advantage by trapping the anion somehow. I’ll do a SciFinder search
later to see if anyone has done something like that before.
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Boffis
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Well done Fery; another nice practical write-up of an often discussed but rarely practiced reaction. I was actually planning to try this myself and
your details with help me greatly. My target is not TNB but 4,6-dinitroanthranilic acid. My plan is to oxide the starting compound to the acid as you
have done and then try o-selective reduction of the sodium salt with sodium sulphide and sodium bicarbonate (as a buffer) in a similar fashion to the
preparation of picramic acid. I have not seen a reference to this use of sulphide reduction so the procedure is speculative.
Nice work, keep it up.
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Fery
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Hi Boffis, that could work. Just keep the 2,4,6 trinitrobenzoic acid always below 55 C otherwise it decarboxylates to 1,3,5-trinitrobenzene (you can
easily filtrate the insoluble trinitobenzene off, but that reduces yield).
Also near the end of the addition of dichromate the mixture becomes quite thick.
Here they used hydrazine + cat. FeCl3 for the reaction -NO2 -> -NH2
https://sci-hub.ee/10.1134/s1070428002120254
Attachment: s1070428002120254.pdf (482kB)
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Boffis
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Whoo Fery, that's a useful find! Save me a lot of experimentation. Many thanks.
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