Sciencemadness Discussion Board - Picric acid: different instructions

Picric acid: different instructions

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Mephisto - 5-1-2003 at 03:30

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.
--------------------------
Mephisto

DeusExMachina - 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.

Rhadon - 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.

DeusExMachina - 5-1-2003 at 09:35

sorry about that.... just trying to help.

DeusExMachina - 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

madscientist - 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.

Mephisto - 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.

Nick F - 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!

Darkfire - 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?

CTR

trinitrotoluene - 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.

trinitrotoluene - 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.

Mephisto - 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.

a_bab - 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.

Rhadon - 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

a_bab - 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.

Mephisto - 6-1-2003 at 16:23

Thank you for the translation! That sounds respectable.

Irrelevant Topic

jacKy - 17-10-2004 at 05:05

Please do not post irrelevant links.

[Edited on 17-10-2004 by I am a fish]

Marvin - 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.

vulture - 17-10-2004 at 10:44

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

Mephisto - 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...

Smoer - 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

Mephisto - 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).

Smoer - 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]

Mephisto - 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.

Smoer - 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

Smoer - 13-11-2004 at 14:21

Thank you for the info and nice pics

.

But I still have a few questions:

Quote:

in kaltem dagegen kaum (0.81 g in 100 g 10 °C kaltem Wasser

Does this mean that in 100grams(=100ml)of water,only 0.81gram of Pa can be solved at 10°?
----------------------------------------------------
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

[Edited on 13-11-2004 by Smoer]

[Edited on 13-11-2004 by Smoer]

Mephisto - 13-11-2004 at 16:17

> Does this mean that in 100grams(=100ml)of water,only 0.81gram of Pa can be solved at 10°?

Yes. This information is from Urbanski (I), page 257.

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

To complete the sulfonation and nitration, heating is necessary. Although I tested this way twice, the time and temperature aren't only my own empirical realization. Since it's almost two years ago, when I write down my synthesis, I can't find today the original source of this information.

Smoer - 20-11-2004 at 08:52

So,I made picric acid

.

Synthese:
First I dissolved 8,4grams of ASA in 50 ml H2SO4 on a temperature between 80° en 90°.After that de solution turned black/brown.Then,I let it cool down to 30° and started adding 18grams of KNO3 to the mixture slowly.First the solution turned orange and after all the KNO3 was added it was red(took me about 40min to add all the KNO3.).I didn't let the temperature rise above 45°.
I heated the mixture up to 120° degrees for 20minutes.The mixture turned brown/yellow.Then I dumped the mixture in ice cold water and immediatly the solution turned yellow.I filtrated the solution and I think its a >70% yield

.

Pictures will follow.

Smoer - 11-12-2004 at 13:23

Hi,

Sorry for the dubble post....But does anyone knows were I can find the solubility of different Picrid Acid salts?(especially Sodium picrate).

BTW: PA yield is 50%

little dissapointed)

cheerz and thanks for answering.

[Edited on 11-12-2004 by Smoer]

Quince - 3-3-2005 at 21:26

I assume ammonium nitrate can be substituted for potassium/sodium, as in other nitrations?

Bert - 3-3-2005 at 22:06

Go here.. Yes, it will work. Sodium or potassium nitrates will work better.

Quince - 3-3-2005 at 23:31

When making a nitrate by neutralizing the easily obtainable weak HNO3 with a hydroxide, I remember I read somewhere that one of the common hydroxides formed water of crystallization, so it's suboptimal for that use. I can't remember if it was caclium or sodium (I have both hydroxides). Does anyone know which one it is?

froot - 4-3-2005 at 02:06

Bert, in my experience I've found that substituting KNO3 with NaNO3 in the PA synth doesnt seem to work. The 'product' is yellow but it completely dissolves in the in the water that's meant to precipitate the PA, whereas KNO3 works fine. The reason for this is beyond me so if anyone knows please enlighten me.

Quince - 4-3-2005 at 07:14

Oh shit! I just spent time making NaNO3 by neutralizing dilute HNO3 with NaOH, not to mention that I fucked up two batches since I poured H2O2 instead of the acid (the bottles are almost identical) before I figured out why the fucking thing kept bubbling...

I thought that the NH4+ ion behaved similarly to K+ in a lot of solutions, so wouldn't NH4NO3 be a better substitute for KNO3?

BTW, I read one of Rosco's posts at roguesci.org, and he suggests making dets with base of picric acid, primary of [4 (basic lead picrate-lead nitrate-lead azide).12 lead azide), and initiator of lead nitrato-bis basic lead picrate. To make this one needs lead nitrate and sodium azide. Where do I buy these two or how do I synthesize them?

[Edited on 4-3-2005 by Quince]

Quince - 5-3-2005 at 00:27

So just to be clear, Megalomania's method uses about three times too much acid?

Edit: I had already mixed the H2SO4 and ASA before I realized it was too much acid, so I just continued with that mix. The color began lightening right away when I started NaNO3 addition (I made the nitrate yesterday, and it had already increased weight by 25% by absorbing water I guess), going from dark reddish-brown to orange. The temperature stayed below 45*C during the ten minute addition, but there was still some undissolved solid. I heated in the microwave to 120*C, which dissolved the solid completely and turned the solution to yellow. There's a good deal of bubbling and acid vapors coming off, and maybe a bit of NOx (hard to tell). It's cooling outside now. I thought the mixture was supposed to turn black again... BTW, my guess is that Megalomania specifies this much acid since it's easier to dissolve the ASA and nitrate in it.

Edit: plenty of precipitate when dumped into cold water, but it went right through the coffee filter. WTF? All I have to show for this are some yellow stains, which especially sucks because I had to synthesize the nitrate too -- basically a heartbreaking disappointment...

PowerLabs says the dinitro- and mononitrophenols are more soluble in water, so perhaps my mix didn't nitrate enough. Or, perhaps it's due to the too much H2SO4 from Megalomania's instructions, making for too much liquid overall, thus more of the PA dissolving. Or it has to do with that I used NaNO3. Has anyone here used this salt instead of the potassium with success in this procedure?

[Edited on 5-3-2005 by Quince]

Bert - 5-3-2005 at 11:59

If you didn't throw away the batch- Chill the filtrate liquid that went through your filter to near freezing. You will see the precipitate re-form. Use several coffee filters in a stack. Don't wash the filtrate with more than a bare minimum of ice cold water. Pre-chill the equipment so it doesn't warm up your mixture to the point that the picric acid can dissolve.

How small was your experiment?

Powerlabs is not a very good source for proper ratios. Sodium nitrate works just fine. Trust Mega.

[Edited on 5-3-2005 by Bert]

[Edited on 5-3-2005 by Bert]

Quince - 5-3-2005 at 13:35

Quote:

If you didn't throw away the batch

I had second thoughts halfway through purging, but...down the sink it went.

My size was 10 tablets. I used acetone instead of alcohol, as in my first try with 99% isopropanol, heating it to evaporate faster made some of the alcohol react with something in the tablets and resulted in some sticky gummy shit.

Is the heating Mephisto writes to 120*C really necessary? Megalomania's procedure doesn't mention it, nor does Brainfever's.

As to which procedure, in an earlier post here the admin says to trust the PowerLabs instead. I'm confused by contradictory recommendations.

[Edited on 5-3-2005 by Quince]

Bert - 5-3-2005 at 13:59

That batch size is so small that you would have very little left after inefficiencies and losses, and could easily have the whole remaining batch dissolve in the water at the end of the procedure with a minor positive error in measurement of the water and/or a slightly too warm water temp. Heating is necessary. Read the whole PA thread on E&W and carefully note who claims to have what yields with which procedure. I should perhaps have said E&W, not Mega

Tiny batch sizes have their place, assuming one is set up to measure accurately. Microtek size batches require microtek precision... Just ask Microtek..

J_O_H_N_Q - 6-3-2005 at 21:24

Why don't you just work it out stochiometrically for yourself?
That way you know it'll be accurate because you didn't just take someone who you've never met before's word on it.

Quince - 6-3-2005 at 22:33

Quote:

That way you know it'll be accurate because you didn't just take someone who you've never met before's word on it.

By that logic: Do you really know the view that the Earth is round is accurate? After all, what if you haven't met any astronaut that has seen it with his eyes?

Plus, my numbers are different from every procedure, so I'm missing something here:

According to PowerLabs, H2SO4 breaks down ASA to acetic and salicylic acids, but it doesn't say any H2SO4 is consumed, so I'm assuming it's just a catalyst. 1 mol ASA makes for 1 mol salicylic acid. This is sulfonated with 1 mol H2SO4, and then it takes 1 mol H2SO4 to make 1 mol HNO3 when NaNO3 or KNO3 is added. So, for 1 mol ASA that's 2 mol H2SO4. With H2SO4 being 1.87 g/mL, that gives with 95% acid about 110 mL for 180 g ASA (that's 554 tablets)! So, since my numbers are so far from everything else (or perhaps this javascript calculator is fucked, http://environmentalchemistry.com/yogi/reference/molar.html), I'm doing it wrong and I have no choice but to pick someone else's ratios.

[Edited on 7-3-2005 by Quince]

Mephisto - 7-3-2005 at 02:55

Quince: Your calculation will give an almost dry reaction-mixture. To avoid the formation of solids in the mixture, the surplus of sulfuric acid is used. Megalomania exaggerates this a little bit. 50 g of ASA in 250 ml of sulfuric acid is a fine ratio.

Here the translation of this method from www.LambdaSyn.tk (German):
******
Add 50 g of dry acetylsalicylic acid and 250 ml of concentrated sulfuric acid to a 600 ml beaker. Heat the mixture 10 minutes to 90 °C, to dissolve the acetylsalicylic acid. Let the mixture cool down and add 87.5 g of dry potassium nitrate or 74 g of sodium nitrate. Add a few grams at a time then wait for the reaction to subside before adding more. During the addition the mixture will turn orange and nitrous gases (!) and CO2 will escape. At this point it should be avoided to let the temperature rise above 45 °C (foaming gets uncontrollable at higher temperatures). Heat the mixture after all nitrate is added and no more foam occurs 15 minutes to 120 °C to complete the reaction. Allow the mixture to cool to room temperature and pour it into 1500 ml of ice water to precipitate the picric acid. Filter the solution to collect the picric acid crystals and wash them with cold water to remove sulfuric acid traces.
******
This method was carried out successfully. If some is interested, there are some pics taken during the method (see attachment).

Attachment: 14pics.rar (467kB)
This file has been downloaded 1800 times

Quince - 7-3-2005 at 03:13

I'm going to try again then.

Has anyone here had success with NaNO3? No one has yet commented on froot's post above:

Quote:

Bert, in my experience I've found that substituting KNO3 with NaNO3 in the PA synth doesnt seem to work. The 'product' is yellow but it completely dissolves in the in the water that's meant to precipitate the PA, whereas KNO3 works fine. The reason for this is beyond me so if anyone knows please enlighten me.

Bert - 8-3-2005 at 09:09

Rosco Bodine quite specifically recommends Sodium nitrate in his procedure. Go do a search of his posts on E&W for the whole post. Picric acid archive file page 2

Once again: more searches = posting less (frequently!) previously answered questions

Cloner - 10-3-2005 at 07:54

The problem with using salts and not nitric is that the already viscous and nasty stuff gets even viscouser and nastier! Among salts, I think KNO3 is the worst choice in solubility. I just tried NH4NO3 and KNO3 and not NaNO3 but for these two salts it is most definitely true. Nitric acid is better, although it is also capable of producing a nasty viscous mass that forms bubbles which do not burst and just come out of the container.

Quince - 12-3-2005 at 19:48

I just used my DIY magnetic stirrer in its first synthesis, picric acid. There was no problem dissolving the nitrate (sodium). Also, I had no problem with sodium nitrate as someone else on this thread did. I used Rosco's procedure that someone linked to above, and even with my tiny scale of 5 g ASA I got about 70% of the stoichiometric yield.

One thing bothers me, though: when boiling down the liquid for the second crop of PA, I did not get any molten red precipitate of impurities, so I just let it crystallize at that point. I wonder if I have a lot of impurities left in that second crop because of that, in terms of anything that may increase sensitivity.

Rosco Bodine - 12-3-2005 at 23:25

No problem . Even with a batch that is 20 times the scale as your reaction ,
the residue of impurity would only amount to about a gram . The way this impurity
is separated out is to boil down the solution left from the first crystallization until a precipitate is observed in the boiling solution . Most of the precipitate is actually picric acid , but it carries with it most of any impurites which form a melt and settle as a globule of red material . This globule will solidify almost immediately as the heat is reduced ,
and will stick fast to the bottom of the vessel as the hot remaining solution is decanted . The decanted solution on cooling will precipitate clean light colored crystals of picric acid free from any " red goo " or impurities which would darken the color .

The second crop of crystals is only about
ten percent of the total yield , so unless
you are working with a fairly large batch ,
the second crystallization is hardly worth the effort .

As for the impurity causing sensitvity issues , probably not .
Any melt compositions of this sort are likely less sensitive than pure picric acid .

Sodium nitrate has been used on a medium industrial scale for batch nitrations producing picric acid in good yield , so it is a well proven method , even though the literature references may be obscure since that method was obsoleted by more modern methods nearly a hundred years ago . Even so , the primitive method can produce yields of 85-90% picric acid from recrystallized aspirin .

The_Davster - 12-3-2005 at 23:36

Has anyone ever gotten a picric acid that is bright yellow(more so than regular picric acid), forms no actuall crystals after recrystallization, does not stain filter paper severly yellow and most importantly burns incredibly fast? I used Mr. Cool's procedure, only 1/10th the scale. Only other difference was that it was crashed into cold water, not ice and water. Could it have formed potassium picrate somehow? It reminds me of potassium picrate when it burns.

Quince - 13-3-2005 at 00:13

One more thing...how do I get PA yellow stains off skin? I mostly used gloves, but at one point I forgot, and it was the worst one to do so -- squeezing out the filter. Washing with water and several solvents didn't do much, and my fingertips are still yellowish...

At least I'm not worried about licking them, as the stuff is incredibly bitter.

[Edited on 13-3-2005 by Quince]

Smoer - 13-3-2005 at 03:41

You can't wash it away...It will stay on your skin for about a week..

BrAiNFeVeR - 13-3-2005 at 04:20

Please bear in mind that at the time the picric acid synth at my site was made, I knew allmost nothing about chemistry.

I clearly state at the entry page that it is probably not the best way to get what you desire.

Now that I have cleared myself of all possible blame and waste of acetylsalicylic acid

I think I actually DID heat the H2SO4 and phenol to make the latter dissolve.

I don't quite remember where I got my procedure from, but I suspect a thread on the old E&W forum.

If I ever have time again

I'll redo all improper synths on my site, and filter it's contents a bit. (like that AP electric detonator ... that HAS to go!!)

Rosco Bodine - 13-3-2005 at 07:26

Picric acid is easily made but there are a few places where people may go wrong .

The sulfonation of phenol or acetylsalacylic acid is a heat driven reaction . The subsequent nitration of either sulfonate precursor is also a heat driven reaction .
Read that as meaning heating to 90 C or better at the end of such reactions for a half hour or more is needed for reasonable completion of those reactions .
The temperature is regulated by rate of addition and by the
level of supplemental heating . A heating bath is what is needed for picric acid nitration , not a cooling bath .

The nitration should be begun with the precursor mixture still relatively hot from the sulfonation , so that the nitration proceeds smoothly and maintains the temperature , consuming the nitration material at rate which follows closely the
rate the nitrate is being added . If the nitrate is added to a cool mixture , it accumulates and then as the temperature rises , a surge in the reaction rate and temperature occurs which is fed by the mass of unreacted nitrate which accumulated at the lower temperature .
So the prevention of a runaway is as simple as beginning the nitration
at a sufficient temperature and maintaining that smooth reaction temperature during the entire nitration . The introduction of each nitro group requires a higher temperature . A working range would probably be in the area of 70 C to 90 C as a minimum , and upwards to 80 to 120 C at the upper limit . That is the temperature " window " for the reaction to proceed smoothly at a decent rate and produce decent yields economically .

The higher temperatures are for the folks who can provide good stirring
and temperature control . The lower range is safer for manual swirling . Longer reaction times and slower additions are needed for the manually done reaction .

The fumes produced by the nitration are deadly poisonous and extreme caution
should be observed to provide some sort
of * steady * ventilation to carry the fumes away . If such ventilation cannot be provided , then the reaction should not be done until that necessity is met .

Otherwise , the " surprise " for the oversight or carelessness will be
much more serious than some stained fingers . The insidious nature of the fumes is that you won't even realize the exposure in real time as it occurs , but 12 to 24 hours later , when the unforgiving learning experience is an unexpected visit from the grim reaper chuckling to himself about how yeah here's another one who just didn't get it . This is one of those perils where " once is enough " ,
no second chances , so respect it for what it is . Accord these sort of nitration reactions with the same seriousness as you would have if poking around with test probes in an exposed circuit panel known to be energized , no slips nor distractions are permitted .

A good test is to put a lighted stick of
incense near the reaction vessel so you
can observe the streamer of smoke as a
telltale for the draft across your work area . If you can smell the incense ,
then you need to get better ventilation
or back away from that area .

The amount of sulfuric acid on Brainfever's site is more than double what is needed even for a mixture that could be swirled manually , and although it probably doesn't decrease the yield it is just a waste of acid .

Quince - 13-3-2005 at 10:48

Quote:

The fumes produced by the nitration are deadly poisonous and extreme caution should be observed to provide some sort of * steady * ventilation to carry the fumes away.

Actually, I did the nitration inside, except for the heating for 3 minutes at 115*C, which I did outside. No brown NO2 was observed, however there certainly were fumes and I no doubt breathed in some amount. Hasn't been 24 hours yet, but I think, given the very small size of my batch, I should be fine.

Are these fumes any different from any other nitration procedure? Is there anything else than NOx gasses and HNO3 vapors that's a problem?

I was more worried about the picric acid on my fingers getting absorbed through the skin, as I read that it's very toxic. Time to steal some more nitrile gloves from the doctor's office...

[Edited on 13-3-2005 by Quince]

Rosco Bodine - 13-3-2005 at 16:48

I stand by what I said about the nitrous fumes . You can play the roulette on this
and one of these times the ball will fall where you hadn't figured . Maybe the
headstone could be engraved ,

" I should still be alive because it was only a small batch , but here I lay feeding the worms anyway . What was I thinking ! "

The_Davster - 13-3-2005 at 16:56

The damage from nitric acid/nitrous fumes does the damage to the lungs heal over time or is it accumulative?

I have had a few lungfulls of these gasses (mainly nitric acid fumes) recently.

Rosco Bodine - 13-3-2005 at 17:25

Maybe you got a whiff or two of air containing a bit of the fumes , but no way did you get a few lungfuls of the stuff ,
because if you did , you wouldn't be telling your own story except in a posthumous publication . There's a few other gases that can do similar damage
from one good breath of the concentrated
fumes , but most of the fatalities are actually from low level exposure which causes no immediate alarm , so a person just keeps breathing the poison until they
have gotten a fatal exposure without realizing it at the time . It's like radiation ,
too much in a certain time window and you are done .

Inhaling a bit of ammonia can be antidotal if you get to it soon enough , but of course only low level there because ammonia is toxic too , just a whole lot less so than the nitrous fumes .

[Edited on 14-3-2005 by Rosco Bodine]

Mr. Wizard - 13-3-2005 at 18:49

Regarding the healing of the lungs, the damage is cumulative, and the lungs do not regenerate. You may pass through an acute inflammation with chemical pneumonia, edema , or fluid in your lungs, and feel better after it passes, but there was damage done. When it comes to breathing toxic fumes and dusts, just say no. Emphysema is a long tough way to die.

Quince - 13-3-2005 at 18:50

How is it possible to get a lungful of HNO3 fumes? For me, they cause my airway to immediately close and I'd have to make an effort to breathe them in.

Rosco Bodine - 17-3-2005 at 06:36

PATR has several references to the extreme toxicity of nitrogen oxides ,
calling them one of the most insidious toxic gases known to man .
The 30 minute exposure to 100 ppm levels is disabling within 48 hours , causing a cardiopulmonary crisis type of episode which can be life threatening , and for exposure at 200 ppm for 30 minutes the effect is fatal .

Expressed as percentages in air , 100 ppm is air containing 0.01 per cent ,
and 200 ppm is air containing 0.02 per cent ......so the stuff is * absolutely *
not a material which can be trifled with by
experimenters . Disbelief of the toxicity
provides no protection . Without any exaggeration , the respect of the inhalation hazard potential in the proximity of nitration and nitrosation type reactions
which evolve nitrogen oxides
is imperative for survival conscious persons working with such processes . The inexperienced may be very watchful and aware of the explosive dangers to the point of distraction , while being complacent and unconcerned about the
inhalation danger , as if it was somehow okay to take it for granted
that this is sensible or safe .

To summarize this information , it is not excessive to have a regard
for the inhalation hazard of nitrogen oxides that very nearly compares to the respect one should have for " intended " toxins like nerve gas . Ventilation measures and avoidance of performing such reactions absent some strategy for avoiding inhalation of the nitrogen oxides even at low levels of exposure ,
is simply a

* NO BRAINER *

[Edited on 17-3-2005 by Rosco Bodine]

Taaie-Neuskoek - 28-3-2005 at 08:04

100ppm is around 188mg/m3, where the odour treshold is 1-6ppm, so you should be able to smell 100ppm as hell...
if I do not smell any NO2, it is fairly ok, if I do smell it --> get the hell out!

Edit: thanks for those instruction about TNP Rosco! I've tried it 2 differend times starting from phenol, and both times I tried to get the temp as low as possible before the first addition of HNO3.
This is causing a very viscious mixture, and after adding a little HNO3, and a little stirring, a kinda runaway happened, with red stuff being blown out of the 1L RBF. Heating up the mixture, and adding the HNO3 slow is indeed a good idea, and if one is really afraid of NOx fumes, (I am) you can do the addition maybe with a reflux condenser on the RBF, cooled with an ice-cold mixture like ice-EtOH. This will trap and liquify some NO2. Though I won't try this probably, as I HATE the smell of phenol...

[Edited on 29-3-2005 by Taaie-Neuskoek]

Taaie-Neuskoek - 23-6-2005 at 06:42

I tried the TNP synthesis again, with the procedure as posted by Rosco. I started from fenol, but some strange things happened...
This is what I did:
I added in a 1L RBF 20gr. of fenol, I added 30ml conc. H2SO4, I transferred the flask to a boiling water bath, and left it there for around 30min.
I added 90ml of HNO3 subsequently in small steps, just fast enough to keep the reaction going. The reaction was visible by a lot of bubbling and the emission of a lot of heat, and a bit of corrosive fumes.
The last 15ml were added at once, and to finish the reaction the flask was transferred to a boiling water bath. The reaction started, went more vigorous, and a shitload of NO2 fumes were emitted. After 30min. the reaction was over, and I let the solution cool down a bit.
I dropped this solution in 250ml of dH2O, froze it, and tried to filter it. I have (I think) around 5-10gr. of TNP. However, besides the TNP, there was also some strange black stuff in the filter, which didn’t dissolve in water at all...
I don’t have an idea of the quality of the fenol, it was already a bit old, so may that be a reason for this? I hope there is enough TNP present to make some azo-clatherate...

Finalising the production stages and purification of Picric acid.

Lambda - 23-6-2005 at 09:26

There is a way to test the completion of the Sulphonisation stage. If you dissolve a sample in Water, then this should give a transparrent solution.

The Picric acid formation, should be completed on a boiling Water bath. This is the final stage to be applied, after no more Nitrogen dioxide (NO2) is produced at the end of the so called "runaway reaction stage". The Water bath heating will allso have been competed, after no more visible Nitrogen dioxide (NO2) is formed.

Picric acid can be purified by:

1. - Washing the filtered crystals with a little amount of cold Water.

2. - These washed crystals are then dissolved in a solution of Sodium carbonate (Na2CO3). A Sodium picrate solution is thus formd.

3. - This Sodium picrate solution is filtered, and Hydrochloric acid is then added. Picric acid then crystalises out as yellow precipitate.

4. - This is then dissolved in the minimum amount of boiling Water, filtered, and then cooled. Picric acid will then precipitate.

5. - The crystaline Picric acid thus obtained, is dried at 30 - 40 degrees C..

Taaie-Neuskoek, you should be able to get rid of that black gunk at stage 3 of purification.

Taaie-Neuskoek - 23-6-2005 at 10:18

I know how purificate the stuff, but thanks for the protocol anyway.
As the gunk is not soluble in water, and TNP is, that is not a big problem.
I am just recristallising the stuff, I've dissolved everything that would dissolve in bioling water + a bit HCl. It is now in the freezer, and I'll let it thaw in the fridge, to minimise the loss of TNP dissolved in water.

The gunk is on a second look not excactly black, but anyway.
However, the gunk is loss, which is a pity. Anyone any idea what it can be, and is it normal?

Thanks about clarification concerning the 3rd stage nitration, the runaway seems to be normal. That's good, but these amounts of NO2 are rather nerve wrecking, even with good ventilation.

Lambda - 23-6-2005 at 10:23

Taaie-Neuskoek, did you get the gunk during the sulphonisation stage, or after the nitration stage ?.

Rosco Bodine - 23-6-2005 at 15:11

The synthesis which I have described was starting from purified acetylsalacylic acid ,
not phenol . Phenol is more sensitive to oxidation in the early part of the nitration and becomes less sensitive to oxidation and temperature as the nitration proceeds .

So the initial to intermediate nitration of sulfonated phenol should be done more gradually at a lower temperature to prevent oxidation losses , and then the temperature ramped up towards the end of the nitration . Phenol nitrates more easily than aspirin so it requires a gentler approach . Others have described some very good results for pretty much unattended nitrations involving specific batch sizes , for picric acid from phenol ,
and there are several variations of a general lab method which all give good results .

Simple recrystallization from a slightly less than saturated boiling water solution allowed to cool * slowly * to room temperature , without cooling , gives the purest crystals . The remaining 10% of the yield can be gotten by boiling down the filtrate until a slight amount of dark molten solid precipitates , decanting
the boiling hot solution and allowing it to cool slowly . Artificial cooling of either of these solutions precipitates impurities along with the picric acid .

Taaie-Neuskoek - 24-6-2005 at 07:37

Rosco Bodino, how would you suggest to keep the temperature of the nitration low when nitrating sulphonated phenol? I’ve tried it a couple of times, but even when is started with a small amount of cooled HNO3 the reaction is very violent and the temperature of the reaction is very hard to control, if not impossible. If HNO3 is added, nothing will happen till the temp and the conc. of HNO3 have reached a certain stage, and it is not advisable to look straight into the flask…

Lambda, The gunk was formed during the last stage of the nitration, before that I could not see any solid material.
Concerning the crystallisation, I know this is not the gentlemen’s way, and will do it the proper way lateron. However, as temperatures are (sub)tropic here, I consider to cool it down a bit more in a fridge, in order to keep the yield a bit high.
I need to get my hands on some ASA, then I’ll try again.

[Edited on 24-6-2005 by Taaie-Neuskoek]

for example

Rosco Bodine - 24-6-2005 at 12:41

See the attached file page 2 , lines 61 through 115 .

For this old text ,

66 Baume H2SO4 is ~ 95.9% H2SO4

42 Baume HNO3 is ~ 68.7% HNO3

There is an indication in this and some other patents that some water content in the nitration mixture can actually improve the yield beyond what is gotten with stronger acids . This would seem to be applicable and useful in particular when the source for the nitric acid is a solid nitrate plus additional sulfuric acid , as the water content would provide a thinner mixture . My own experiments with the nitration of salicylic acid disulfonate derived from aspirin indicate that somewhat less dilution with water should be used when a nitrate plus sulfuric mixture is used for nitration , than is described by the patent for the nitration of phenolsulfonic acid using nitric acid . I would guess that the difficulty for the nitration of a particular phenolsulfonic precursor has a bearing on what concentration is optimum for the nitration mixture , and the concentration may also differ according to the type nitration mixture used , whether it be using a solid nitrate , or free nitric acid , or some combination . But the process would seem to be general , and also applicable
to synthesis of styphnic acid and other nitrophenols . The optimum proportions and temperatures and times would vary some for each particular scenario .

[Edited on 25-6-2005 by Rosco Bodine]

Attachment: US1380186 Picric Acid Manufacture.pdf (301kB)
This file has been downloaded 1622 times

Taaie-Neuskoek - 25-6-2005 at 12:10

Thanks a lot for the patent Rosco!
However, no quantity is given for the amount of HNO3 to be added for the introduction of the 2nd and 3rd nitrogroup, but I assume it must be 2.2 molar ratio to the amount of phenol.

Rosco Bodine - 25-6-2005 at 16:22

Honestly I have never looked too closely at methods for picric acid using phenol as the precursor , nor have I ever made any picric acid from phenol , simply because it is the least convenient and most expensive precursor . OTC precursors like
aspirin , salicylic acid , and oil of wintergreen , have always seemed more promising as starting materials . And honestly again aspirin is the only precursor I have ever used for making picric acid , since it is cheap and I get about 90% yield . From what I have read
about the published methods , I would likely just use an adaptation of the method I already use for aspirin . I haven't tried this adaptation to see how it would perform or know what adjustments would be needed to refine the method . This is purely off the top of my head as a possible experimental method as I am interpolating and guessing a bit on this adaptation for phenol . I hesitate to describe an untested experiment because of the unknowns , but anyone having some experience " reading " reactions as they are observed could try this approach and
make their own adjustments as it goes to
pin down the details . So for the got carbolic acid on the shelf but got no aspirin folks , here goes nuttin'

If you just want something different from one of the reported methods known to work , this seems possible , but I am not
entirely certain , this is hypothetical at this point .

This proposed method is untested and
most definitely EXPERIMENTAL :

The reaction contemplated would be performed in a two liter beaker or wide mouth erlenmeyer or flat bottomed florence or a similar sized pyrex teapot ,
sitting upon a stirrer hotplate with a good thermostatic heat control , not a rate controller , and using a three inch or larger
stirbar . A thermometer , addition funnel and wash bottle will also be required .

50 grams of liquified phenol is added slowly with stirring to 200 ml 92% H2SO4 @85 C , regulating the rate of addition to
maintain reaction temperature of 95 C to the end of the addition . The temperature is raised to 115 C and maintained for an additional 30 minutes and then the heating discontinued .
When the mixture has cooled to 55 C ,
the stirred mixture is cautiously and slowly diluted with 75 ml H2O streamed onto the walls of the vessel from a syringe or wash bottle .
To the stirred mixture is added in small portions dry sodium nitrate , at a rate sufficient to maintain temperature in the
range of 55 C to 70 C , or just less than the temperature at which red fumes appear , until a total of 60 grams sodium nitrate have been added . Then an additional 200 ml 92% H2SO4 is added at
a rate which maintains the temperature at
65 C . When the addition is completed ,
the temperature is maintained with supplemental heating for fifteen minutes
at 65 C , and then raised to 85 C . In small portions an additional 120 grams of
dry sodium nitrate is added to the stirred mixture as rapidly as the rate of reaction allows without producing red fumes . The
temperature rise allowable should steadily
increase as the nitration proceeds , particularly after the midpoint of the addition . A smooth nitration temperature
may be observed in the range of 95-100 C. At a point towards the end of the addition of the nitrate the exotherm should begin to diminish , and supplemental heating should be applied to maintain the reaction temperature with an endpoint temperature of 115-120 C ,
held for three or four minutes , before
supplemental heating is discontinued .
Stirring should be continued for the mixture as it cools . After the mixture
has cooled to perhaps 80 C , it is again
cautiously diluted with water streamed
onto the inside wall and allowed to sheet
slowly into the stirred mixture , ~300 ml
of water being used for the dilution .
The still warm mixture is dumped onto twice its volume of ice cubes . After standing for a time all of the ice will be melted and the cold mixture is filtered to obtain the crude picric acid . The still damp crystals are redissolved in boiling water and recrystallized on slow cooling to room temperature . The filtered solution is concentrated by boiling until
some dark colored precipitate appears , allowed to cool slightly and decanted from the impurity . Upon cooling slowly a second crop of crystals will be obtained ,
about 10% of the total yield from the second crop of crystals . The total yeild
should exceed 90% of theory based on phenol , about 110 grams of dried crystals of pure picric acid .

[Edited on 26-6-2005 by Rosco Bodine]

Quince - 14-7-2005 at 23:38

I was using generic ASA tablets. I initially filtered after soaking in a bit of water to dissolve the hydroxypropyl methycelluose. After drying in air, I dissolved in acetone and evaporated it. However, no crystallization appeared. Instead, a thick, dirty-colored liquid remained, with a smell a bit like vinegar. My guess is I overheated during evaporation (I was using a heating mantle, so the beaker walls were much hotter than the base with the fluid, and probably little cooling to the base from evaporation), but I'm wondering what the likely decomposition products are?

[Edit] Fuck, it's impossible to get rid of the sticky shit! I had to scrub my hands with hot ammonia to get rid of it, and I'm still cleaning the beakers! Motherfucker!

[Edited on 15-7-2005 by Quince]

Oh man, hot ammonia does a number on your skin. My hands are redder than a spanked indian ass.

This sticky goatsassshit is worse than the time I got picric acid dust in my mouth. And I don't know what the hell it is, was it the fact that I used generic ASA, or what.

[Edited on 15-7-2005 by Quince]

Removing the binders from aspirin

Rosco Bodine - 15-7-2005 at 05:34

Here is a good method for isolating the pure acetylsalicylic acid .
When aspirins are on sale , you can buy two bottles of 500
325 milligram tablets for under five dollars . After weighing the thousand 325 mg tablets , and doing the math , you may find that you have about 53 grams more weight than the 325 grams of pure aspirin the tablets contain . There are different solvents and methods that can be used for extracting the acetylsalicylic acid , and I have tried a few
different ways , discovering that denatured alcohol works very well for this .
About 800 ml of denatured alcohol will dissolve your 325 grams of aspirin , if you get the alcohol solvent hot . A procedure I have used that works well is to first break up the tablets the easy way by letting moisture do the work of breaking the binders . Dump the 1000 aspirin tablets into a stainless mixing bowl of about one and one half liter
capactity . Put some water into a trigger sprayer bottle and very lightly mist the tablets while stirring them around so that their entire outer surfaces are moistened , the idea being
to just dampen the all the outer surfaces of all the tablets slightly , but not to soak them . Complete the task of moistening the tablets quickly , because
in less than a minute , the tablets will begin disintegrating , and you should not continue misting the powder , or a wet mud will be created instead of the damp but loose powder desired . The moisture will cause the tablets to disintegrate to a powder as they are stirred . There will be small pieces that may be a bit stubborn but these can be crushed under the pressure of a spoon after sitting idle a few more minutes in the dampened powder . The job doesn't have to be perfect , because later the alcohol used to extract the aspirin is going to complete the task of disintegrating any small chunks of tablets . The loosened damp powder is spread out in a glass tray to air dry . A good method for drying this and other materials is to get a large retangular glass ovenware baking dish .
Underneath the tray place a heating pad of the sort used for soothing sore joints and muscles .

Beneath the heating pad should be placed a sheet of styrofoam or a stack of newspapers , or a piece of fiberglass insulation batting so the heat path is to the drying tray and not wasted warming the tabletop instead . An efficent tool for breaking up a dried crystal cake is one of those potato masher kitchen utensils which has heavy wire formed into a flatted section having U-shaped , back and forth parallels with the wire forming a yoke which enters a handle . The dried aspirin powder is spooned into a glass jar of about one and one half liters capacity , and having a threaded closure . Then about 700 ml of denatured alcohol is poured ino the jar and the mixture stirred . The jar is capped lightly and placed into a pan of warm water then heated further , to a bit less than boiling hot by a hotplate . It is not necessary to get the alcohol hot enough to boil , but do heat to nearly the boiling point of the alcohol .

The jar of alcohol and powdered aspirin will be brought up to nearly the boiling point of the alcohol and all of the acetylsalicylic acid should dissolve in the hot alcohol with a little stirring , and the starches and buffers should settle out of the solution into a layer on the bottom of the jar . The sediment is a very fine dustlike material , and it will be difficult to decant all of the clear solution without disturbing the sediment and contaminating the supernatant clear solution . Filtering the saturated solution is out of the question without a heated funnel , because the saturated solution will begin crystallizing immediately on exposure to the air from evaporation
and cooling while pouring , which will instantly plug up any filter . The manipulation should be performed as follows : Carefully decant as much of the clear solution away from the layer of sediments as possible without stirring up and tranferring sediment along with the
hot solution . The hot solution is decanted into the cleaned stainless bowl which was used earlier for breaking up the tablets . It will serve well as a crystallizing vessel . Whatever solution cannot be decanted away without being contaminated by sediment , must be diluted with an added 50 ml portion of alcohol.( in order to lower the saturation and reduce the tendency to crystallize during pipetting ) and the
solution is reheated on the water bath . The solution can be taken up into a large irrigation syringe and transferred portionwise to the bowl for cooling . Alternately , a pickup wand ( glass tube ) can be used to vacuum pickup the liquid and deliver it to an aspirated receiver bottle , but only a very gentle vacuum may be used to prevent flash boiling the hot alcohol in the receiving bottle . I have a 100cc syringe that I use for the transfer . A large rubber bulb, automotive battery filler , or a turkey baster type of utensil would probably work as well for harvesting the supernatant liquid without disturbing the sediment . Once as much of the solution above the sediment as possible has
been transferred to the crystalizing bowl , a further 50ml portion of alcohol is added to the remaining sediment and swirled with it , then this is simply dumped through a coffee filter . The filter is twisted down to squeeze the sediment into a ball and press out the alcohol , and the filtered solution is added to the solutions in the crystallizing bowl . A lump of sediments which is the binders and other inert materials now having been separated from the original aspirins , will be about the size of a golf ball or slightly larger , a substantial amount of impurities removed . The cooling bowl of crystallizing pure acetylsalicylic acid should be set if front of a small fan or blower to keep a good stream of air across it , and the bowl should be warmed gently at the same time . The source of heat should be low power ,
like a water bath of small dimension which does not quite reach the boiling point , a potpourri crock , or a heating pad is adequate , or one of those heated coasters that are used to keep a coffee cup warm should work fine .

A mound of crystals will form quickly in the bowl and if the crystals are periodically scraped from the sides and piled in the middle of the bowl into a pile which rises above the surface of the liquid , a wicking effect will cause a small mountain of crystals to grow in the evaporating solution .

Several hours will be required for the crystallization to complete , and then the mass is dumped out into a warmed glass tray , broken up and dried comletely . The cake of crystals will be most easily broken up while it remains slightly damp with residual alcohol , and if allowed to dry completely without breaking it up , it will become a very hard rock , a monolith which will require jackhammers and dynamite to reduce to powder . So save a lot of work and begin breaking up the crystal cake while it is still damp . After the material is fully dry and broken up , store it for later use by keeping in an airtight container in a cool dry place .
A freezer is good for long term storage of the pure material .

[Edited on 15-7-2005 by Rosco Bodine]

Quince - 15-7-2005 at 14:46

The only high percentage alcohol available here is isopropyl alcohol. However, every time I've tried it, it reacts with something in the aspirin and makes a sticky mess. This is the first time I've had acetone fail, and I'm not sure what went wrong. Also, aspirin here is about $10 for 100 325 mg tablets.

Quince - 20-7-2005 at 20:14

The aspirin here contains triacetin, which is soluble in alcohol. How would one separate this from the ASA, when alcohol extraction would extract both?

The old fashioned coffee grinder as powder milling machine

Lambda - 21-7-2005 at 16:43

An old fashioned coffee grinder can be used to grind the asprin tablets to a fine powder. The blades in such a coffee grinder are blunt-edged, and the powder formation is based more on impact than on the cutting action. This works out fine for making powders. You must not overburden the grinder with to many tablets at the same time, for the motor will then overheat rapidly if used in many succesive batches.

Just adding my two cents.

Quince - 21-7-2005 at 22:25

Look here at the aspirin purification part. He crystallizes the ASA by cooling a filtered saturated alcohol solution. I like the idea, since I have problem with heating decomposing the aspirin. However, to use this alternative procedure, the approximate solubility of aspirin in the alcohol is needed.

Anyone know what the ASA solubilities in isopropanol and in acetone are? Couldn't find this during my searching.

Also, my triacetin question from the last post didn't get a reply. It's soluble in alcohol, so the impurity remains with the ASA; what about acetone, or some other way to remove it?

[Edited on 22-7-2005 by Quince]

Joeychemist - 21-7-2005 at 22:34

US patent 2890240 relates to, and deals with the purification of aspirin via crystallization from acetone, it may help you, if not, it is still very relative to this thread and the subject at hand.

Quince - 21-7-2005 at 22:55

The patent was useful for the solubility data (ASA/acetone w/w 0.62 @ 55*C, 0.22 @ 10*C).
The method itself is not suited to home use due to the replacement solvents given (carbon tetrachloride or benzene).

Rosco Bodine - 22-7-2005 at 05:32

@quince

Denatured alcohol is a common article of commerce , a solvent / fuel that the Canadian revenue page lists a dozen different formulations in virtual agreement with US formulas , so I can't imagine why there is any problem finding it in Canada .

Aspirin sold in bottles labeled " Aspirin " should be pure aspirin as required by law consistent with the label , containing only inert binders for holding the tablets together , and it should be the cheapest medicene on the shelf anywhere even in grocery stores . Aside from that you could just get veterinary aspirin powder by the pound which is probably pure acetylsalicylic acid . If neither of these options are available , then you might try using oil of wintergreen ( methyl salicylate ) instead . I haven't tried it myself , but it has been reported by others to sulfonate and then nitrate in a similar way to aspirin , and requires no purification .

Accident report

Quince - 28-7-2005 at 20:19

Well, I had my first runaway nitration. I had the NaNO3 in one beaker, and the ASA in another. Since I didn't have enough NaNO3, I made up the difference with KNO3, except I mistakenly added the KNO3 to the beaker with the ASA instead of the one with the NaNO3. You can guess what happened when I started adding H2SO4 to the former. Instant huge brown cloud. I reacted quickly, but nonetheless I did breathe in some, especially in the time after the cloud dissipated, but there must have been a good deal left due to the poor ventilation, as I'm feeling the pain now in the lungs. I did breathe in ammonia several times, so I don't know if it's an excess of nitric acid or ammonia in my lungs that's causing the pain. The beaker was filled with hot brown stuff, which is hard to wash, so I tried bleach, which turned it PA yellow. I don't know if I should go to emergency, as they'll probably call the cops and I'll be in shit. Should I breathe in more ammonia, or is too much danger of overdoing it?

[Edited on 29-7-2005 by Quince]

neutrino - 29-7-2005 at 06:24

I doubt they'll ask too many questions. If they do, tell them that something at school/work went wrong.

Bert - 29-7-2005 at 06:49

To quote ATSDR:

Quote:

There is no antidote for nitrogen oxide poisoning. Treatment for exposure usually involves giving the patient oxygen and medications to make breathing easier.

ATSDR/Nitrous oxides poisoning

To quote Roscoe on page 3 of this thread:

"The fumes produced by the nitration are deadly poisonous and extreme caution
should be observed to provide some sort
of * steady * ventilation to carry the fumes away . If such ventilation cannot be provided , then the reaction should not be done until that necessity is met .

Otherwise , the " surprise " for the oversight or carelessness will be
much more serious than some stained fingers . The insidious nature of the fumes is that you won't even realize the exposure in real time as it occurs , but 12 to 24 hours later , when the unforgiving learning experience is an unexpected visit from the grim reaper chuckling to himself about how yeah here's another one who just didn't get it . "

Rosco Bodine - 29-7-2005 at 07:30

@Quince

I hope it isn't serious , and you learn something from the carelessness at no greater cost than some worry .

If with passing time you are feeling worse instead of better , seek medical attention .
They will probably have you inhale some sort of mist medication like albuterol or similar medication such as used for people
having asthma or having gotten smoke inhalation near a fire .

Really I don't mean to make you feel worse for saying so , but you should do more reading and thinking about what you are doing , and have more situational awareness when you are handling chemicals and doing experiments .....or
else you should find a different interest than experimental chemistry .

Betaine

Rosco Bodine - 29-7-2005 at 09:27

In another thread the usefulness of
Betaine ( vitamin B14 , IIRC ) as a stabilizer referenced in GB191405737 is mentioned . Betaine binds chemically with up to one half its own weight with nitrous and nitric radicals which makes it a useful stabilizer . Since betaine is also
a low toxicity naturally occurring substance in the body , actually a vitamin ,
it would seem to be a good candidate as an antidote for exposure to inhaled nitric
oxides . In exactly what form it may be useful as an aerosol mist inhalant , perhaps as some buffered lactate or citrate or combination in proportion with
the freeform betaine , is unknown . But the possible usefulness of betaine as an antidote is there , if the betaine formulation could be taken as an inhalant
without causing some adverse reaction itself . Medicene is not my area of expertise , but if betaine has not been investigated as an inhalant antidote for nitric oxide specifically , but some betaine medication for inhalation use already exists for some other purpose , this may be something for a doctor to consider as
an off label use in certain circumstances .
It may be that this is already known and tried , or used but not commonly known ,
or something already ruled out for some reason . Or it may be one of those things that has never been tried , in which case it may be an idea worth testing .

Quince - 29-7-2005 at 22:03

I feel fine now. From what I read, medication is supportive only, at most steroids are given. I think quickly going for the ammonia may have helped me out here. The problem with the ammonia is that it itself has a fairly unpleasant feeling. I guess the worst that happened this time is all the wasted time I spent purifying the ASA...

An ounce of prevention ......

Rosco Bodine - 30-7-2005 at 04:56

Ajantis - 4-8-2005 at 07:57

Ok, I attempted my first picric acid Synth, with powerlabs procedure.
I started from 20g salycilic acid and my yield is 25g, 70% of the theoretical, some PA had been lost during the filtering. I had no problems with the procedure exept when adding nitric acid to phenol 4 sulphonic acid... i perfomed this step outdoor, my acid were chilled to -15C so the reaction took about 20 min to begin but when it started a HUGE cloud of NO2 developed, i've never seen so much NO2 in a time, the cloud was about 6m long, and at 10m distance i could clearly smell its odour

So, Be careful with this step!

RLMAO!!

Joeychemist - 4-8-2005 at 08:28

Quote:

Originally posted by Ajantis
I had no problems with the procedure exept when adding nitric acid to phenol 4 sulphonic acid... i perfomed this step outdoor, my acid were chilled to -15C so the reaction took about 20 min to begin but when it started a HUGE cloud of NO2 developed, i've never seen so much NO2 in a time, the cloud was about 6m long, and at 10m distance i could clearly smell its odour

So, Be careful with this step!

That sounds to me like you had a partial runaway reaction

There should not be a giant cloud of Nitrogen Oxides, but only a very small amount produced during the entire reaction. Did the temperature rise considerably?

If it was a partial runaway you are very lucky that you did not get hurt, but next time you may not be so lucky...

[Edited on 4-8-2005 by Joeychemist]

picric acid ? from methyl salicylate

Rosco Bodine - 8-8-2005 at 19:01

Many years ago around the first time I made picric acid from aspirin , I also tried
using methyl salicylate . It is also called oil of wintergreen for the product steam distilled from the natural leaf , 99.7% pure for the expensive medicinal grades .
Anyway my first experiment was not successful , but some years later about three and a half years ago a post was made at E&W by vonK reporting success ,
and I have done a couple more experiments to study the reaction further ,
and also to evaluate some ideas that may be more general with regards to picric acid synthesis from any precursor . Alternative precursors to phenol are of most interest since phenol is expensive and not essential . Refinements to the nitration are also of interest . After only two preliminary experiments which are not yet fully completed I am still far from being able to provide description of a good working method or optimized synthesis from start to finish . However I can share some interesting observations and ideas for others who may also want to work on this line of research . I would encourage the novices to be patient and let the more experienced pursue the experiments , especially any of the sizeable scale batches . These experimental nitrations have not yet been evaluated fully or established to be predictable or safe .

Two experiments have been performed which have produced substantial amounts of picric acid from methyl salicylate . The product is not yet isolated and dried so I cannot give the yield .

Experiment 1 :

50.5 grams ( 43 ml ) of methyl salicylate was added to 250 ml of 92% H2SO4 .
A mild exotherm 10C rise on mixing was observed . The mixture was heated to 135C and held at 135-145C for 3 hours .
A white thin vapor appearing like wisps of steam would slowly come off during the sulfonation , but the vapor had a stifling odor like formaldehyde or dimethyl sulfate and was avoided , taken away by powered ventilation .

After allowing to cool to 45C , 40 grams of NaNO3 was added in small portions to the well stirred mixture , about a third teaspoon at a time . Rate of addition was used to maintain about 70 C , each addition allowed to dissolve and slight foaming to subside before the next portion being added . The intended mononitration seemed to peak on its own exotherm at about 74C and then began cooling . Likewise addition of a second 40 gram portion of NaNO3 was begun . This
went more rapidly due to lower exotherm after each addition . Foaming was observed but appeared to be decarboxylation foaming predominately , with no substantial red fumes below 74C ,
but at 75C and induction of sorts with sudden foaming of the threatening sort appearing . In hindsight , this is where I should have probably added supplemental heating to force induction and slowed the additions to keep the reaction controllable but driving it at a higher temperature . But what I did instead was to allow the exotherm to peak at 75C for the dinitration . 90-95C would have probably been better , and some holding time for maybe 20 minutes
before proceeding to the trinitration stage . A final addition of 30 grams NaNO3 was made at the 75C , with little
change being noticed during the time the portions were being added . 75C was too low and so after a few minutes some
supplemental heating was applied , and all it took was the little nudge of 5C for the nerve wracking little third stage runaway . I managed to mitigate the foaming with increased stirring and a few
small squirts of water from a wash bottle onto the surface of the foam . But the frothing continued and the mercury was at 115 C and climbing rapidly when I aborted the uncontrolled reaction by dumping the flask into a large bowl of water . There was a red cloud of nitrous
fumes roiling from the angry looking mixture which wasn't quenched a moment too soon , and some of the fragments of reaction mixture were molten picric acid way above the safe temperature . Some of the material I think actually sublimed from the heat and condensed onto my ringstand a couple of inches away . But most of the flask contents got into the water quickly and the batch was salvaged at the point of reaction which was well towards completion when the runaway occurred . Picric Acid was definitely made
from methyl salicylate , but the reaction conditions need some more experimentation and refinement . The purity of the product by color appears to be excellent , very pale yellow . The crystallization for some reason seems to go much slower than for the product made from aspirin . The initial yield after dilution of the reaction mixture looks poor , but the crystals continue to precipitate slowly over many hours in the cooled mixture and even more when it is cooled very cold to freezing temperature to harvest the crystals by filtration for recrystallization from boiling water . Whatever is the impurity from the use of methyl salicylate , seems to make the crystallization not as crisp as the product from aspirin , solutions seem to linger in superstauration and then deposit more slowly a finer and softer product . It may require a second recrystallization to get the same quality , or refinement of the nitration may clean up the crystallization which follows . Admittedly I did not stop the crystallization as I usually do with the solution still slightly warm at filtering which produces a more shiny and crunchy product , but cooled the solution to drop more of the product out because I was in a hurry to simply salvage the batch , and see what sort of weight I salvaged . I knew I could recrystallize later when I can add the product to a crystallization of a larger batch(es) and save labor fooling around with separate crystallizations for each small yield from several test batches . I like to work up at least 3 liters of solution for a crystallization of picric acid because it seems to require that minimum amount to get good crystals . Smaller quantities don't seem to have the thermal mass for slow enough cooling to form good crystals .
Others have observed the same peculiarity .

Experiment 2 :

This experiment took a different track for the nitration , where I decided to try some ideas I have kept wanting to test concerning the presence of water in greater amounts in the nitration mixture .
After sulfonation I diluted the mixture with some added water before the nitration . And instead of portionwise additions of a solid nitrate , I used a dropwise addition of a strong solution of a nitrate . Departing from convention I also used ammonium nitrate because of its high solubility , and because its conversion to nitric acid in sulfuric acid is actually facilitated by the presence of water . This scheme worked and produced a good yield in the end , but like the first experiment the process definitely needs refinement . The mononitration stage was extremely slow and sensitive to temperature at about 50 C seeming optimum , and requiring literally all day to complete . This would likely have to be automated , unless some workaround could be devised to expedite the mononitration . The dinitration and trinitration go smoothly and fairly rapidly at 95C and 115C respectively , but the mononitration is tediously slow . Much of the decarboxylation seems to occur in the mononitration stage which is good , and I believe it is the water content which accounts for this . In nitration mixtures having low water content , for aspirin the decarboxylation seems to occur in the trinitration stage when the viscosity of the mixture makes the foaming problematic if the reaction rate surges even a moderate amount . In the thinner
mononitration stage , with water present and the precursor being methyl salicylate the effervescing foam dissipates easily .
Then the higher nitration proceeds smoothly with any remaining decarboxylation occuring just before the end of the nitration . The nitration mixture is a transparent yellow liquid as it approaches the endpoint at 115 C and is effervescing freely as if an alka seltzer was boiling away but producing no red fumes , only a thin wisp of azeotropic nitric acid vapor from the acid in excess .
The effervescing stops and then the mixture becomes cloudy but no solid picric acid precipitates until the mixture is dumped onto an equal volume of ice cubes and allowed to stand for several hours when a heavy precipitation occurs .
The precipitation is not immediate as occurs when aspirin is the precursor . Because of the delayed precipitation the yield at first appeared poor , but a few hours and some time in the freezer brought the precipitation to completion .

Experiment 2 details :

Methyl Salicylate ( 82 ml ) was added to 395 ml of 92% H2SO4 and the mixture was heated to and held at 145C for 4 hours . The heating was discontinued and after an hour the mixture had cooled to 85C and was covered and set aside overnight .

The next day the sulfonated mixture was diluted with 70 ml distilled H2O dripped slowly onto a thermometer leaning in the flask . The water flowed down the thermometer into the stirred mixture without causing any undue heating or acid splattering . The valve on the funnel was preadjusted to a slow drip rate while held over an empty beaker , and then the funnel emptied before positioning over the flask . Then the dilution water was added in small portions to the funnel to keep it replenished , so it acted as a preset flow regulator and the addition rate was controlled from the first drop .

While the sulfonated mixture was diluting ,
a nitrating agent was prepared separately . 194 grams of NH4NO3 was dissolved in 130 ml hot distilled H2O . Total volume was about 255 ml for the solution . It was filtered through a cotton plug to remove a small amount of suspended matter . A first portion of 100 ml was used for the mononitration of the diluted sulfonated precursor . The addition literally required all day at a very slow drip rate of about 8 drops per minute and reaction temp ~50C for the most of the time . The reaction was very sensitive to any attempts to drive it faster and would respond to any increases with foaming and red fumes . An infusion pump and a close temperature controller might be necessary for any practical use of this method , if the conditions cannot be modified to improve efficiency . I suspect that the high ratio of water to nitric in such a mixture is highly oxidizing instead of preferentially a nitrating mixture in its effect . The desirable aspect is that most of the decarboxylation
is achieved simultaneously . There is likely some modification of this mixture which can run faster and still be stable and this will require some process engineering , otherwise known as trial and error, to discover what is optimum

At the end of a long day , when all the first 100 ml of NH4NO3 solution had been added to the stirred mixture . The stirring was stopped and the dark red mixture set aside to fizz and stew overnight .
The mixture was returned to the hotplate stirrer and the temperature was gradually raised to 90C for the addition of the 80 ml
of solution estimated for the dinitration .
The rate of addition was allowed to bring the temperature up to 95C which was maintained by rate of addition . As the reaction proceeded there was no red fumes but continued mild effervescence .
Supplemental heating was increased to maintain 95C at the end of the addition .
And then the final portion of 70 ml NH4NO3 solution was added to complete the trinitration , with supplemental heat ramped slightly and maintaining 110 degrees with endpoint at 115C held for about thirty minutes past the end of the addition . Stirring was stopped and the clear yellow liquid gradually became cloudy as the nitration completed . Heating was stopped and about 15 minutes later the mixture 800 ml in volume was dumped onto an equal volume of ice cubes to dilute and cool and precipitate . The crude crystals are still in the filter , pressed to a hard lump and drained , a coffee filter full to the top edge weight unknown .

Anyway , from these two experiments is some information which may be useful in further experiments towards refining the method for methyl salicylate , and perhaps applicable to aspirin as well .
The ability to add the nitrate as a solution is definitely of interest , as is the use of NH4NO3 for the nitrate . It may be of benefit to use the solid nitrate for the mononitration in the absence of so much added water in the stage where it causes oxidation to be aggravated , and then bring the added water into the system at the dinitration stage where it seems beneficial . The reactions work , but refinements and streamlining the process are definitely needed for this to be a straightforward method as with aspirin .

IPN - 10-8-2005 at 07:31

I recently made a batch of picric acid from ASA (50g) by the method D from lambdasyn.tk
So, nitration went well and a good yeild of product was obtained and I started to recrystallize it by dissolving in 1l of boiling DH2O.
After dissolving, I placed the 2l beaker aside and wrapped it in some cloth. Some hours later it was still warm and to my suprise the picric acid had formed _big_ platelike crystals. Would it be safe to crush the crystals or should I reheat and let it cool a bit faster?

neutrino - 10-8-2005 at 07:50

Definitely reheat and cool faster, e.g. dump onto ice. Big crystals are much more sensitive and dangerous than smaller ones.

IPN - 10-8-2005 at 08:11

Ok, that's what I'm doing now.

Here's a pic of the crystals.

picric_acid_crystals.JPG - 132kB

don't fear the crystals of picric acid

Rosco Bodine - 10-8-2005 at 09:00

@IPN

Crystals are what you want , and slow cooling of hot concentrated solutions is the way to get them . When the solution is even still slightly warm , the best crystals have already formed . More crystals will precipitate with time , and at cooler temperatures if weight is what you want instead of a desirable physical form .
So if shiny well formed crystals which filter easily and dry more quickly are your desired form for the product , then you have to give up some weight and filter while still slightly warm . Then you concentrate the residual solution and take a second crop while still warm , or just cool it and drop out the remaining yield as the finer more powdery form .

I am experimenting with simplifying and taming the synthesis so that large batches of even several hundred grams can be made in a crock pot by a reaction which may take awhile but can be run unattended for most of the process . From what I am observing a presence of some water content in the nitration mixture is desirable , and also the greatest exotherm for the nitration occurs in the mononitration . It may be possible to start the mononitration at about 55-65C and then use a cooling bath in order to hold down the temperature at about 50C and allow for a more rapid completion of the mononitration stage . The remaining nitration goes much more smoothly once the mononitrated phenolsulfonic stage is completed , and the final nitration is more safely conducted , absent any tendency for runaway . The precursor becomes more resistant to oxidation or decomposition in the mixture after it reaches mononitration , so that is the first hurdle to get past , and decarboxylation early in the process is a bonus , which gets most of any foaming problems out of the way early in the nitration .

Some futher experiments are definitely in my plans , for both aspirin and methyl salicylate starting material , and using a solution of ammonium nitrate instead of solid nitrates . These potential improvements should make it possible to make sizably larger batches in a safe and controlled predictable way , which involves a lot less labor than the solid nitrate and more anhydrous nitration mixture methods . I really think I am onto something here with these experiments .
It is something which has probably been done before since it seems so simple ,
and the reaction conditions and behavior of the reactions is in agreement with the descriptions of industrial methods found in several old patents from nearly a hundred years ago . This is sort of "lost art" which I am looking into , and there is already experimental evidence that such technique can simplify synthesis of picric acid in ways which are entirely scalable upwards without difficulty or danger .

neutrino - 10-8-2005 at 11:51

Sorry, I must have been thinking of some other explosive I came across in Mega's lab. I could have sworn that PA and dumping onto ice went together somehow.

Rosco Bodine - 11-8-2005 at 03:23

The time that ice is used is when the spent nitration mixture is diluted . An equal volume to twice the volume of ice seems about right . I like about twice the volume of ice cubes because that dilution is one which allows for a paper filter to survive the filtration so long as the filtration is completed within a couple of hours . A less diluted reaction mixture will complicate filtration by weakening the filter paper to the point it is disintegrating some time later when the crystals are rinsed from it into water for the boil and recrystallization . The reason ice is used is to absorb the exotherm from the heat of dilution for the highly acidic spent nitration mixture which is itself still warm and carrying a lot of heat in its mass already which must also be dissipated ,
along with the heat of crystallization which is given off as the picric acid drops out of solution . If just the right amount of ice is used , it should all be just finished melting about twenty minutes after dilution of the spent nitration mixture and the mixture should be cold .
The solubility of the picric acid is low in the cold diluted nitration mixture and most of it will precipitate within three hours if the mixture is kept cold and allowed to stand .

Picric acid readily forms supersaturated solutions in nitration mixtures and also in plain water , and takes its time crystallizing from solution , there being several hours delay to achieve the crystallization endpoint for a given temperature which defines the solubility .
So patience is required to see what amount of crystals will finish forming at any given temperature , and the warmer the finishing temperature for the crystallization , the more noticeable is the sluggishness for the crystallization . There is no way to rush the process at near ambient finishing temperatures . I let my crystallizations stand at room temperature for a day or two before regarding them as complete , but at least six hours would be a good rule of thumb .
A lot of still dissolved product will be lost if the process is rushed and filtered too early . When boiling down a concentrated solution of picric acid , the solution will become cloudy at the point where the boiling down needs to be ended , after adding a little makeup water to reclarify it and drop it below saturation . If any filtration of suspended material is needed to be done in advance of the first crystallization , an addition of maybe 5% of the cloudpoint volume of fresh water back to the boiling mixture will
be sufficient to keep the solution from crystallizing during the cooling it encounters while being filtered through a cotton plug in a funnel . Sometimes this may be needed if impurities are evident in the solution in the first boiling , and it is desired to clarify the solution for a cleaner first crystallization . Better crystals are obtained from a very transparent solution which has been polished by minimal filtration to remove any overt particulate impurities .

Ajantis - 11-8-2005 at 06:49

Quote:

Originally posted by Joeychemist

Quote:

So, Be careful with this step!

That sounds to me like you had a partial runaway reaction

I don't know if temperature raised considerably because i stayed safely far away

however Sam said that large amounts of nitrogen dioxide would develop during this step...

Rosco Bodine - 11-8-2005 at 08:22

Extreme cold is likely counterproductive for the mononitration , unless you are using nearly anhydrous acids and are using the cold to hold down the reaction rate . Because of the extreme cold slowing the reaction , what would be likely is an accumulation of unreacted acid and then an uncontrolled sudden rise in reaction rate when after the temperature
clowly climbed to an induction point . The idea for controlling a reaction is to have your reaction proceeding smoothly at a temperature where the reaction rate can be controlled by the addition rate . Once those conditions are identified , then you can scale up or down without having any uncontrolled surges to cause difficulty or danger .

The induction temperature may be above or below the steady reaction temperature by some amount , and it may change somewhat as the reaction proceeds . But usually there is a sort of happy medium temperature where most of the reaction will proceed smoothly for each stage .

The best mononitration temperature is going to depend somewhat on the water content and acid ratio in the nitration mixture . And the mononitration stage is more sensitive to rate and temperature than are the dinitration and trinitration .
For your particular nitration mixture you will have to experiment and take notes to identify the conditions which give good results . From these notes you can then develop a sort of graph from which you can learn the optimum conditions and then have a reproducible method .

Quince - 12-8-2005 at 23:37

Hi, the cheapest ASA here contains propylene glycol. When looking up solubility, it dissolves in acetone and alcohol. What if I wash the aspirin with a bit of water first (which I already do to remove the hydroxypropyl methylcellulose)? ASA solubility in water is about 1/100 w/w. For propylene glycol, the datasheets just say "miscible" for water solubility, so I'm not sure if that's more or less soluble than the ASA.

Rosco Bodine - 13-8-2005 at 07:08

The amount of propylene glycol is likely
very small , and used as an anti-dusting agent . Simply leaving a small amount of alcohol when the bulk is evaporated from the growing mound of pure aspirin crystals will likely trap the small amount of propylene glycol in that residual alcohol .
At cool temperature it won't be carrying much aspirin , but the residual alcohol can be diluted with water to precipitate the bit of aspirin still remaining and leave the propylene glycol in the diluted alcohol . It would likely be better to go this route than to crash the entire batch into water .

From what I have seen from my experiments with methyl salicylate , I will never again go through the trouble of purifying aspirin for use as a precursor again , so long as the wintergreen oil is available without too great of an expense or difficulty . The yield was 75% from my first clumsily done experiment described above , which would have been more if there had not been the runaway I encountered for carelessness and unfamiliarity with visual markers for the progress of the nitration . And the yield appears even better for the second experiment which I will be filtering soon .

I really like the advantage of being able to use a liquid 60% solution of Ammonium Nitrate for the nitration , which eliminates the labor of purifying and recrystallizing sodium nitrate fertilizer in advance and then later having to make portionwise additions of the solid nitrate , conducting a " spoon fed " nitration and getting a thick and ill behaved mixture towards the end . It is really a quantum leap in simplification to be able to work with a liquid 60% solution of the nitrate , and an even cheaper nitrate as a bonus , and be able to regulate the addition by drops from an addition funnel instead of adding a solid by fractions of a spoonful at a time over what can become a long period of tedious labor .

The purity of the product is also excellent with none of the red colored byproducts often seen from aspirin nitrations . I have a lot of purified aspirin on hand which I plan to use up also in testing the new nitration technique using 60% NH4NO3 solution . I see no technical reason why this same method would not be general for phenol as well , and also for other nitrophenols , styphnic acid , ect. and it
is on early evaluation a technical improvement in the nitration methods which do not use nitric acid , perhaps even superior also to those methods which do .

Picric Acid is such a fundamentally versatile energetic material that it would seem worthwhile to add to the knowledge available about its synthesis and purification particularly in terms of lab methods which are efficient and safe .

Sorry for being longwinded , but the sight of my two liter Erlenmeyer with a beautiful layer of sparkling glitterflake picric acid at the 450 ml mark in 1650 ml of clear pale yellow liquid volume , from a never before described nitration method using 60% Ammonium Nitrate solution and
92% Sulfuric Acid , has me smiling gleefully like a kid finding a new toy .

Once in awhile I still stumble across something which is an interesting find ,
* very interesting * to the point of raising an eyebrow and making me smile , and this is one of those times where a little advancement in the art or a lost art just soft landed in one of my flasks as a copious amount of the desired product in highly pure crystalline form

So I am inspired now to try to pin down the details for a method I know works well , and that you probably won't find described in a book or paper anywhere ,
but is technically superior to anything similar you may find .

Now I must pause , breath on my fingernails and buff them against my chest with pride , realizing how hard it is to be modest when you know you're great

[Edited on 13-8-2005 by Rosco Bodine]

Quince - 14-8-2005 at 22:57

Well, just at the end of nitration, my thermometer broke and the mercury got mixed with everything. Down the drain goes another batch I worked hard on...

Rosco, I can't wait until you post the details of your improved procedure.

Well, I guess I have to wait to get a thermometer again...shipping from the US == another couple of weeks

IPN - 15-8-2005 at 01:02

You used the thermometer to stir the mixture? And mercury down the drain?

Anyways, I decided to make the big crystals again as Rosco suggested. I filtered the crystals when temperature was still about 40C (no crystal growth occurred anymore) and got 26,52g (from 50g of dry crude material) of light yellow, dry, big platelets which were then gently crushed with a plastic spoon on some tissue paper. Seems to be quite pure (sharp meltingpoint)

Rosco Bodine - 15-8-2005 at 06:11

What I said earlier about the probability of
much knowledge about picric acid having become lost art is confirmed by PATR . It is a very old material which was seriously studied and used in the time of and by Glauber , and also known to the alchemists even earlier , was used as a dye for a long time , then later as an explosive , before falling out of use and disappearing for the most part from the literature before it was well documented ,
nearly a hundred years ago . So picric acid is an oldie but a goodie , most of the knowledge about which was once common , but the book on it was never written and the knowledge lost with the end of the days of those who knew about it . In the present , picric acid is largely a historical obscurity with regards to finer details concerning its most efficient synthesis and crystallization .

The crystallization behavior of picric acid is peculiar , and I suspect there are different crystalline forms that are temperature dependant , with both size and form varying with temperature and the concentration . The nature of what trace impurities are present also seems to influence the crystallization . I keep separate samples from different syntheses and each sample seems a bit different in form from the others gotten from different processes . The crystals are fragile and even vigorous stirring of the wet crystals will actually mill them to powder . There is a point where gentle stirring will stir down the crystals to a more dense layer but more stirring beyond that causes the volume of the layer of more and more broken crystals to increase and keep increasing until a slurry of fine powder results which does not separate . So the stopping point has to be early so as not to overmanipulate the material and lower its bulk density by
more than minimal action with the stirrer .
The fragile crystals dislike being jostled around , and are readily " fluffed " by even gentle abrasion . The stirrer does the same thing to solutions having standing crystals as does a coffee grinder do to the beans , first chopping up the chunks , and then multiplying that volume
in chopping the chunks to a light powder .

The best crystals seem to form from a somewhat less than saturated boiling solution allowed to stand undisturbed to grow a crystal " tree " on very slow cooling to a still barely perceptible warm to the touch temperature , and then filtering the mass broken up only by the minimal disturbing of the structures needed to transfer them for filtration . Literally spooning the crystals onto the filter is what you have to do to keep the bulk volume of the final resultant dried product fairly high . I have been trying to find the optimum dilution and holding temperature for the crystallization . And I suspect that a holding time at maybe 40C may benefit the crystal growth if a batch is simply allowed to stand for an extended time while held at that slightly warm temperature .

From a dozen crystallizations I have only twice hit the conditions just right and gotten good clean and dense well formed crystals which dry to a desirable free flowing glittering crystalline form . The other ten times have produced a mixture of those crystals with the fines which clump on drying . Chemically of course it is all the same , but I really like for the end result to be a consistent physical form . So far I have found no way to obtain the desirable form crystals except from that portion of the crystallization which occurs in the warm range , and then harvesting that crop , later
concentrating the solution to a similar point , and repeating the process which is tedious . This is precisely why I like to work with large batches of picric acid , because of the labor involved in the crystallization . It is almost impossible to get good results unless you are working with nearly a gallon of the near saturated boiling solution at the beginning , because smaller quantities lack sufficient thermal mass for the slow cooling rate which is necessary for good crystal formation . I have even considered that
doing these crystallizations in a Dewar flask , or a foam insulated container would
likely be of great benefit , since it would extend the cooling time and thereby allow for the crystals to grow in the more slowly cooling solution . But even something as simple as wrapping a fiberglass batt around a container of the boiling hot solution , sitting on a sheet of foam , will greatly extend the cooldown time and result in larger crystals . There is an amazing difference in what drops out of solution slowly over a day or more , compared with what preciptitates in a few hours when the cooldown and crystallization is more rapid . This inconvenience about the crystallization behavior of picric acid has likely accounted for the premature discarding of many experiments by impatient persons who
poured down the drain supersaturated solutions which would have produced crystals in large amounts if simply set aside for a day , or set up solid if deeply cooled for a few hours . Picric Acid is one fickle bitch to crystallize in the way you might want it to behave , and may have to be coaxed with varying conditions to produce good clean crystallizations from water solutions . If such efforts for
water solutions are unsatisfactory , and this is likely for smaller batches , then the
more practical approach is to use cold to drop out the greatest yield of precipitated product as fines , and after drying , then recrystallize from hot alcohol , simply letting the alcohol evaporate to get gritty dense crystals .

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