potassium/sodium picrate

Hi all, as it is my first post I hope to be not too stupid and I apologize for my poor english I'm reading this forum for a few months and I think my question should have a place here.

Today I made some potassium picrate using powerlabs method (from picric acid using the i-ve-no-phenol-so-i-use-ASA way). I filtered some crystrals which (when dry) looks yellow (darker than picric acid). I took the solution and make it evaporate by sunlight (I'm not crazy since I used only 1g of trinitrophenol and had filtered most of the potassium picrate in step #1). When they were dry they looked dark orange (maybe red but you know colours...)

So I tried burning a few micrograms of picric acid, Kpicrate #1 and Kpicrate #2.

I'm now sure that #1 and #2 are NOT picric acid. both burned the same way but the #2 (dark orange) burned slower with more black carbon cloud.

So, do you have any idea ? Thx for your replies !

EbC Title.

[Edited on 16-12-2005 by chemoleo]

Hi sylla,

Way back when it was ok to make home made fireworks. My father made them. He used black powder for some and a bright yellow powder for some small but powerful crackers. He always refused to tell me what it was. I now think it was a picrate.

The fact that may be helpful to you is when it was ignited it left a whitish powder mark not a black black one.

Have fun but be carefull Bob

Sodium Picrate

Pictrates!

Sylla, I have already aswered this question by mail to you but it was in french...so I can't simply copy paste it

More than certainly the first compound you get is the normal picrate salt...yellower than picric acid...important point but we get to this later.

You evaporated your remaining solution under the heat of the Belgian sun ...note that the place shoudn't influence the result ...the result is dus a mix of the same picrate but with an increasing concentration of the exces base...pH gets higher and higher....

Now let's get to a little theory for all those really interested in chemistry....
I will consider only the tiny portion of the aromatic ring placed just between the C holing the HO of picric acid and the C holding the ortho NO2 group...for convenience purpose, I will draw everything on a sheet of paper, scan it and this wil be joined as attachement.
The effect is thus true for any ortho nitrophenol...via an intra molecular mechanism. (I have taken the + and- sign of the nitro group away to simplify the drawing)

Note the formation of a ceton and of a nitronic acid patern!

As a parallel I have put also the equation for nitromethane...eveyone who has played with this and with a base has noticed the colour that appears...yellow...if yellow is concentrated it is orange, if more red...then brown and finally black...

Note that the aci form in the alcanic familly is more sensitive than the nitro form...this is the reason why bases are sometimes used to sensitise nitromethane...

This fact is true for the aromatic familly...especially if an exchangeable hydrogen is in the direct vicinity of a nitro group...

TNT is relatively unsensitive and yellow...by heating with NaOH...one could get an orange-red form of TNT that is more shock sensitive...
Here the proton transfer is harder than in TNP and so warming and conc NaOH is needed.

With picric acid the proton transfer is achieved in water at a feeble %...this explain why picric is nearly white yellow when dry, yellow when dilluted, makes very yellow picrates and forms orange/red colors in exces base...

No will to impress you at all!

I have made a mix of Ni(NH2-NH2)3(NO3)2 (usually pale lilas-pink) coprecipitate with NH2-NH3O-C6H2(NO2)3 (hydrazine picrate-pale yellow).....the original pink complex had turned that way pale brown.
In the mix probably Ni picrate, Hydrazine picrate and nickel trihydrazine dinitrate complex...properties not very wel studied owing to the lack of made material (a few mg)...burns fiercely but difference with the original nickel nitrate hydrazinate not noticeable at that quantity...
I'll certainly come back on that study since I have plenty of Ni(NO3)2 at home, about 300g TNP, and about a kilogram of hydrazine sulfate...
And then I'll try to set a testing up to compare:
1)Ni(NH2-NH2)3(NO3)2 (pink)
2)Ni(OC6H2(NO2)3)2 (?colour?)
3)(Ni(NH2-NH2)3(NO2)3)x.(NH2-NH2-O-C6H2(NO2)3)y.(Ni(OC6H2(NO2)3)2)z (pale brown)



[Edited on 17-12-2005 by PHILOU Zrealone]

[Edited on 17-12-2005 by PHILOU Zrealone]

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Philou, thx for your reply but if you look at the post it has been done 2years ago so it's a different question actually Note that your mail did actually reply to the problem too...

I recently had another trouble (that I had discussed with philou by email) with picric acid salts. To resume the experiment I have tried a new approach on ammonium picrate because the current way of doing it is dangerous (consist of evaporating ammonium picrate solution that is very soluble). Unfortunately my picric acid was still moist (because of remaining H2SO4 of the synth) so I did a easy purification consisting of reacting it with KOH to produce potassium picrate and then reacting it with conc HCl to precipitate "pure" picric acid (as it as already been mentioned by someone above). The resulting picric acid was droped into acetone and shacked. The first amazing thing is that my moist picric acid dissolves very well in acetone as it should but purificated picric acid doesn't (even 1g in 100ml acetone yield nothing!). Then I filtered the so called picric acid and let it dry. This was very quick and gave me beautifull yellow crystals (much more yellow than the moist one). Then, I placed a coffee filter on a beaker containing conc ammonia (btw horizontal the filter, just to use some "porous paper") and the crystals on the top of the paper. After about 5minutes they turned orange but (not red as my potassium picrate tends to be). Another interresting thing is that it does detonate from flame! it is not as loud as silver carbide but quite surprising since picric acid nor potassium picrate does that.

Note that you pointed an error of massic ratio in my calculus leading to a large excess of HCl so if someone try to reproduce the experiment he should use 1ml HCl 30% per g K2CO3 used to neutralize picric acid.

You also suggested to prepare a solution of picric acid in ethanol and add drop by drop a amoniac/ethanol solution. The resulting ammonium picrate would then precipitate. (But then why just don't doing it in solid/vapor phase as I tried ? )

I need to point out that the so called ammonium picrate describe above has been tested "neutral" with K2CO3 (no CO2 evolutions) while it shows acidic before beeing exposed to the ammoniac. This could prove it worked.

You ended your email with several quotes to explain the detonation. I'll translate and resume them so everybody can work on the topic too.

1/ DNP or TNP way be present.
2/ The CompD might detonate that way.
3/ (the following part was painfull to understand for a undergraduate student like me so tell me if I killed the spirit of it) There is a enol-cetone-nitronic equilibrium with TNP that makes the darker form which is more sensitive (nb: indeed this would explain my very first post here). The same way, TNB and TNT have a red form in strong alkaly conditions that makes them more sensitive. This is because of a deprotonation that shifts the nitronic equilibrium (like it occurs in nitromethane). This is known for Comp D where a red form, more energetic, has been identified but it goes back to its normal form over time. -CO-C(=NO-ONH4)- <--> -C(-ONH4)=C(-NO2)-

If anybody have a little time to investigate on these energetic forms it would be great because picric acid is a so common synthesis for a lab amateur... At the end, I remember that styphnic acid has the same color problem and one could make a yellow form or a, more sensitive and more energetic red form. The difference here is that it doesn't flip back to its yellow form... Anyway, it's kinda normal to have these similitudes sinces styphnic acid shares a lot of structural properties with picric acid !

Good night everyone

[Edited on 11-1-2006 by sylla]

Seems I have troubles again with my picric acid :p

I left some PA in a dessicator for about one month with piperic acid made from piperine close to it and... on the surface the picric acid changed to very dark purple color :-/

Could some kind of piperidinium picrate have formed ? What could explain such a color ? :-/ And well, most of all, could it be dangerous (sensitive or else) ... ?

Sorry for the troubles of such silly questions

Sylla,

That's an interesting observation.

Perhaps a deliberate experiment could be conducted by gently heating an alcoholic solution of piperic acid and adding the picric acid to this in portions with stirring (methanol or ethanol should work fine), to see if the addition compound forms.

Picric acid forms addition compounds with a great host of organic compounds, cinnamic acid is an example of this; the addition compound in the case of cinnamic acid has a melting point of 106.5 *C.

The general trend with nonmetallic, organic picrates is that they are more insensitive to impact than picric acid itself is, ammonium and gaunidine picrate for example. Even the majority of the metallic picrates are less sensitive to impact than picric acid itself is. For example, in a test reported by Davis, a 2 kilogram weight being used to test the samples, sodium picrate ignited by a drop of 17 inches, aluminum picrate 16 inches, picric acid a drop of 14 inches and these are all the minimum hieghts at which ignition or detonation occurs. All the hydrated picrates reported in the table have a minumum drop height greater than that of picric acid!

The key to these tests is that the picrate is crushed between two hard surfaces. Not to mention that 2 kilograms is alot of weight to be dropping on a picrate, prepared in the lab, on accident. My point being that in practice, handling picrates and indeed picric acid itself is not a major safety concern unless you plan on hitting it with a hammer! You probably wouldn't want to eat the stuff, or breathe it in, either.

However, another safety concern that should not be overlooked in handling any energetic material is static electricity. The experimenter should always have himself grounded at all times to avoid static discharges into the energetic material from the human body. Many accidental explosions have occured because of this very problem. A copper wire (exposed) and wrapped around the experimenter's wrist or ankle and grounded in the proper manner should illiminate this problem.

In the case of the addition compound (if any) formed by reaction of PA with piperic acid, a good test for it's energetic properties is the hammer test, in very small amounts mind you! This gives a sense of sensitivity and power of the material being tested.

By the way, Sylla, do you know which isomer of piperic acid you have or is it a mixture of isomers?

Magnalium would probably do much better with the CuO compositions, added benefit is that the MgAl alloy is mucht easier to tumble into a powder as well (compared to Al or Mg alone). Lead tetraoxide is easily produced from lead + acetic acid --> carbonate precipitation --> Heating to oxidize basic lead carbonate with O2 from the air, although I agree cumulative toxic compounds like heavy metal salts are best avoided.

@Dornier, agreed, the total enery release is not affected much by heating probably, though the ability of the shockwave to accelerate fast is THE most important factor determining the initiating performance (brisance) on a weight basis for primaries used in blasting caps. Azides accelerate immensely fast and single crystals can make DDT, while total potential energy release for leadpicrate/styphnate is probably higher. The only difference is that the latter accelerate much slower and don't reach a high VoD in the small amount in which they are used. Most regular chlorate whistle compositions example can reach 2500 m/s in bulk amounts and BC initiation, but in gram amounts and fuse ignition they only reach about 800 m/s or lower. Audibly they may sound the same and could be definined as detonation as in faster than the speed of sound, though the former will be much more brisant.

Anyway, testing is the only way to find out, I'll give it a try...

Here's high speed footage (240 fps) from four tests:
Molten KClO₃ / NaC₇H₅O₂, 4 mg


Molten KClO₃ / NaC₇H₅O₂, 30 mg


KClO₃ / NaC₇H₅O₂ in powder form, 50 mg


KClO₃ / KC₆H₂N₃O₇ in powder form, 50 mg


The two first were detonations. The two last gave very loud blasts and turned the paper tubes into fragments (on average 5 mm) but were not complete detonations. Look at the flames shooting out. Last one also coloured the tape yellow.

[Edited on 3-8-2014 by Dornier 335A]

[Edited on 3-8-2014 by Dornier 335A]