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Author: Subject: Picric acid: different instructions
Mephisto
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[*] posted on 5-1-2003 at 03:30
Picric acid: different instructions


I found large differences in the instructions for the synthesis of picric acid.

For Megalomania’s method you need 24 ml of phenol and 14 ml of concentrated sulfuric acid (only for the sulfonation). For the nitration you need 46 ml of 72% sulfuric acid and 175 ml of 70% nitric acid.

For the powerlabs-method, you had to take 31,25 ml of concentrated sulfuric acid for 25 grams of phenol. Then you need 47 ml 68% nitric acid. That’s nearly one quarter of the amount of the nitric acid, as in Megalomania’s method.

The differences in the relation between phenol sulfuric acid and nirtic acid are very irritating (also for the time of the sulfonation). As the sulfuric acid is a reagent and needed for dehyrdation, it is hard to calculate the right amount of it. URBANSKI describes a method with 4 moles of sulfuric acid for one mole of phenol, but this is quite more, as in the ohter intructions. Small amounts of nitric acid would lower the yield, but high amounts of it could oxidize and destroy the picric acid. So, has someone any idea of the right amounts?

Sorry for my ugly english.
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DeusExMachina
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[*] posted on 5-1-2003 at 08:38


"Picric acid:


Introduction:
Picric acid has a detonation velocity of 7480 m/s and has a melting point of 123 degrees Celsius. It's quite toxic and is absorbed through skin. Breathing the dust of the dry powder is also dangerous. Respirator and gloves should be worn when handling this explosive. Picric acid will form dangerously sensitive picrate salts if it is exposed to metals.

Materials:

125 aspirin tablets containing 325mg acetylsalicylic acid

220ml 98% sulphuric acid

77g potassium nitrate

500ml 99% isopropyl alcohol



Heres a picture of the chemicals needed to prepare picric acid. From left to right there’s potassium nitrate, sulphuric acid, 99% isopropyl alcohol, and aspirin (acetylsalicylic acid)







Procedure:
The first thing we must do is purify the aspirin and remove any fillers or binders in the pills. After this step, you'll have pure acetylsalicylic acid. We do this with isopropyl alcohol. This process must be done in a place with very good ventilation. When purifying aspirin, you must evaporate large amounts of alcohol. This is safe if done outside, but can be very dangerous if done without proper ventilation. Powder 125 aspirin tablets each containing 325mg of acetylsalicylic acid. Pour the powdered aspirin in a beaker and set it aside. In another beaker, warm 500ml of 99% isopropyl alcohol to 60 degrees Celsius in a simmering water bath. When the temperature of the alcohol reaches 60 degrees, remove it from the heat source and add the powdered aspirin. Vigorously stir for 2 minutes then filter the liquid through 2 coffee filters and keep the filtrate. Discard the aspirin impurities left in the coffee filter. Pour the alcohol/aspirin solution into a shallow dish and gently heat it in a hot water bath until all of the alcohol has evaporated leaving pure acetylsalicylic acid. On the right is a picture taken after the aspirin was added to the alcohol.



In another beaker, add the acetylsalicylic acid to 220ml of 98% sulphuric acid and heat it to 70 degrees Celsius on a simmering water bath. Hold the temperature at 70 degrees and stir until all of the acetylsalicylic acid has dissolved. After adding the acetylsalicylic acid, the solution usually turns black. I would have taken a pic of this change in colour, but my sulphuric acid is black so there was no colour change. Once all of the acetylsalicylic acid has dissolved, remove the beaker from the heat source. While vigorously stirring, add 77g of potassium nitrate over a period of 1 hour. Add a little more than a gram per minute, while constantly stirring. During potassium nitrate addition, nitrogen dioxide is given off. Do this step outside or somewhere with very good ventilation. When potassium nitrate is added, the colour of the solution changes from black to red/orange then back to black. When most of the potassium nitrate has been added, the colour of the solution in usually very dark red, although not always. To the left is a picture of the solution after a small amount of potassium nitrate was added.





After the potassium nitrate addition, let the solution cool to room temperature then cool it to 5 degrees in an ice bath. Once the liquid has been cooled to 5 degrees, you should have a suspension thick with picric acid crystals. On the right is a picture of the picric acid suspension after being cooled. In another beaker, add 500g of ice to 200ml of water. While stirring the ice/water, slowly add the picric acid solution. Wait 15 minutes for the picric acid to settle at the bottom of the beaker, then pour off 500ml of the liquid and add another 250ml of water. Filter the liquid through 2 coffee filters and discard the filtrate. The yellow solid left in the coffee filter is picric acid. In another beaker, bring 200ml of water to a boil. When the water starts boiling, remove it from the heat source and add the picric acid and stir for 5 minutes. Cool the picric acid solution to 5 degrees by using an ice bath and then filter off the picric acid using 2 coffee filters. Now you have reasonably pure picric acid. "

once I get my KNO3 and H2SO4 I'm going to try this method.
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Rhadon
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[*] posted on 5-1-2003 at 09:33


DeusExMachina, I'm sure you posted this procedure with good intent, but Mephisto did neither want to start from acetylsalicylic acid nor did he he want another synthesis at all: He just wanted to know what would be the best amounts of phenol, sulfuric and nitric acid one could do a picric acid synthesis with.
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DeusExMachina
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[*] posted on 5-1-2003 at 09:35


sorry about that.... just trying to help. :(
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DeusExMachina
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[*] posted on 5-1-2003 at 09:37


damn this edit button! I guess I should have rea the post more carefully. I'll look for what you need right now
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madscientist
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[*] posted on 5-1-2003 at 10:26


I would definitely go with the Powerlabs synthesis. Any procedure that measures phenol in milliliters is not very good. With the Powerlabs synthesis, I suppose you could use the same amount of nitric acid, but more concentrated, to cause the nitration to proceed more smoothly.



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Mephisto
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[*] posted on 5-1-2003 at 11:07


Thank you, madscientist. But in the technical process, the sulfunated product is diluted with water, because of the high oxidizing effect of the concentrated nitric acid. So I think, I shouldn't use concentrated nitric acid.

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Nick F
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[*] posted on 5-1-2003 at 11:13


I don't see anything wrong with measuring phenol by volume, since it melts at 43*C it'd be easy to melt it and pour it. Also, I find it has a habit of solidifying in its jar, and melting it is the best way to get it out.
Although if this is what he meant he really should have said so, I agree that measuring a solid in mL is obviously no good!
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[*] posted on 5-1-2003 at 21:27


I dont think isoprophyl alchohal is a good idea to use, i didnt work right when i used it.

Why do you need nitric acid? Isnt mixed acid good enought?

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[*] posted on 5-1-2003 at 23:15


If you want to make larger amounts of it then there is a different method. You will have to make it from Benzene. I think the method is on megolmainas site.But I will go with Brainfevers method. Aspirin pills contain different amnouts of ASA so I guess brainfevers method is better off If you dont know how much ASA is in there.



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[*] posted on 5-1-2003 at 23:21


Sorry for the double post.
Ok I can see why Isprophyl alcohol dosen't work.I can tried to extract the ASA with 70% Isprophyl alcohol before but when I boiled it away my ASA turned to acetic acid. I guess the reason why Isprophyl alcohol dosen't work is because it contains water.water will cause you Pheno of ASA to change to something else I think Acetic acid. And I guess If yuo can calculate it might work. But maybe its better off to use the method where yuo use asprin pills.




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Mephisto
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[*] posted on 6-1-2003 at 04:04


All in all that’s fine but I’m interested in the phenol+H2SO4+HNO3 method, not in the catalytic process nor in the ASA method. I know the procedure, only the right amounts are unknown for me. Maybe, I try at first the powerlabs-method, so I wouldn’t waste much nitric acid.

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a_bab
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[*] posted on 6-1-2003 at 04:40


Try this one. It's a russian method for labs.

94 grams of phenol (1 mole) should be heated at 100 degrees C and add 300 g of H2SO4 monohydrate under agitation. Heat the mix for 1 hour at 100-110 degrees C, then cool it down to 0 degrees C. Under exterior cooling (less than 0 degrees C) and energical agitation, add drop by drop a mix formed of 220 grams (3,5 moles) of HNO3 of 98 % and 220 grams of H2SO4 monohydrate. After all the sulfonitric mix has been added, left the mix at the room temperature overnight and then heat it at max. 45 degrees C, for an hour with agitation. Because the reaction is not finished at 45 degrees, 50 ml from the reaction mass is taken out and heated on a sand bath at 110-125 degrees C. In the heated mass the rest of the mix is added drop by drop under energycal agitation. Afterwards is should kept at 120 degrees and some water should be added until the H2SO4 will be 40 % concentrated (about 700 ml of water). If the reaction was conducted in good conditions a small quantity of NO2 will be released. TNP which will crystalize on cooling and it's not soluble in H2SO4 40 % will be filtered, and washed with cold water. The total amount of TNP obtained it'll be around 210 grams.

Nevermind the mistakes as I translated this on the fly.
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[*] posted on 6-1-2003 at 09:49


This method may have high yields but unfortunately it uses 98% HNO3. If ~70% HNO3 can be used instead I'd use the latter without any doubt, because it's so much easier to get / doesn't need to be concentrated at first.

Additionally, such highly concentrated HNO3 is already reserved for RDX synthesis :D
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[*] posted on 6-1-2003 at 15:11


This is the original method but using 70 % HNO3 should work assuming that you'll use more sulfuric acid.
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Mephisto
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[*] posted on 6-1-2003 at 16:23


Thank you for the translation! That sounds respectable.
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[*] posted on 17-10-2004 at 05:05
Irrelevant Topic


Please do not post irrelevant links.


[Edited on 17-10-2004 by I am a fish]
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[*] posted on 17-10-2004 at 07:43


Probably worth pointing out even at this late stage that technical phenol containing a little water is actually a liquid.

I also notice that the powerlabs synthesis contains a little less nitric acid than would be theoretically required for complete production of picric acid. Not a comforting sign as we'd normally expect this to be in excess even for pure nitric acid and somewhat larger excess for 70%.

For people that want to use 70% acid, I would be inclined to use the method in Davis.
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[*] posted on 17-10-2004 at 10:44


There's a standard method for nitrating phenols in Organikum too.



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Mephisto
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[*] posted on 17-10-2004 at 11:09


In the end, I decided to use the method from Gattermann ('Die Praxis des organischen Chemikers'; ebook available on the ftp). This method uses nitric acid with a density of 1.41 g/cm³ (≈ 68-70%). It worked fine for me, although I used phenol with 10% water in it.

That's actually 21 moths ago, how time passes...




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[*] posted on 12-11-2004 at 12:08


Could someone please give me the right intructions for PA with the KNO3+H2SO4 method.

Has someone tested the method of DeusExMachina or Brainfever??If so,wich of them is best?

Thank you for helping
Smoer
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Mephisto
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[*] posted on 12-11-2004 at 13:17


I also carried out the ASA+KNO3+H2SO4 method successfully.

Since you're from Belgium, it's slightly possible, that you understand a little bit German. If so, you will find the right instructions here (method B). If not, I can translate it for you (tomorrow).




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[*] posted on 12-11-2004 at 13:27


You don't need to translate it but thanks:cool:.

So,I have only 8,4grams of ASA so I should use 46ml H2SO4(50ml to be sure) and 16grams of KNO3 if I use the synth of DeusExMachina .

If I use your synth I should use 42ml of H2SO4 and 15grams of KNO3.

heres not much difference between the 2 so prolly it doesn't mather wich synth I use?or does it?

cheerz

[Edited on 12-11-2004 by Smoer]
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Mephisto
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[*] posted on 12-11-2004 at 15:04


Smoer: Yes, it doesn't matter which of both methods you use. It doesn't harm to take a little bit more (H2SO4+KNO3).

And here some old pics of my synthesis.


1. Dissolved ASA in sulfuric acid
2. Adding KNO3 to the mixture (to much at once would cause nitrous fumes)
3. After adding the whole amount of KNO3
4. After 10 minutes at 120°C



Precipitated picric acid in 1.5 L water.




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[*] posted on 13-11-2004 at 14:21


Thank you for the info and nice pics;).

But I still have a few questions:
The synth in this topic says you have to heat the ASA+H2SO4 at 70°,then add the KNO3 en let it cool down to 5°.

But your(Mephisto's) synth says you have to heat it at 90°,then add the KNO3(temp below 45°) and then heat it for 15 min at 120°.

So what is the best way en why is heating necessairy(because brainfever doesn't heat it).

Thank you for answering.

cheerz
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