Sciencemadness Discussion Board - Checking purity of RDX

Checking purity of RDX

IndependentBoffin - 30-4-2011 at 23:51

If one were to prepare a small sample of RDX (about 10g) by the acetylation of hexamine to DAPT (3,7-Diacetly-1,3,5,7-tetraaza[3.3.1]bicyclononane) and then nitration with 70% nitric acid in the presence of glacial acetic acid, acetic anhydride and ammonium nitrate (scaled down from Ledgard, J. "Prepratory Manual of Explosives" method), what are the methods used to confirm the purity of the sample?

Explosives testing is out because it won't tell you if a sample is 90% or 99% RDX anyway. Also of interest is in ensuring there are no unstable secondary byproducts which may sensitise or decompose the otherwise relatively insensitive + stable RDX.

quicksilver - 1-5-2011 at 07:41

Purity testing would remain similar no matter the method of synthesis. Melting point, utilitarian attribute, physical microscopic examination of a carefully re-crystallized sample, etc, etc, etc.
MP should be right at 202 C (use a damn small sample!) As some other nitroamines it's (RDX) found to have a great level of ammonia; thus in a mp test there should be a characteristic odor.
Much more significantly a well shaped, clean crystal will react to diphenylamine with a vivid blue color.

hissingnoise - 1-5-2011 at 08:26

Quote:

RDX (about 10g) by the acetylation of hexamine to DAPT (3,7-Diacetly-1,3,5,7-tetraaza[3.3.1]bicyclononane) and then nitration with 70% nitric acid in the presence of glacial acetic acid, acetic anhydride and ammonium nitrate (scaled down from Ledgard, J. "Prepratory Manual of Explosives" method).

Wouldn't it be easier and simpler to just add hexamine portion-wise to strong nitric acid and drown the mixture . . .
The precipitated RDX, when washed, has sufficient purity for technical purposes, according to Davis!

IndependentBoffin - 1-5-2011 at 08:31

Yeah but that method requires producing WFNA first. The DAPT method requires 70% nitric acid which is much more readily available.

IndependentBoffin - 1-5-2011 at 08:39

Quote: Originally posted by quicksilver

Purity testing would remain similar no matter the method of synthesis. Melting point, utilitarian attribute, physical microscopic examination of a carefully re-crystallized sample, etc, etc, etc.
MP should be right at 202 C (use a damn small sample!) As some other nitroamines it's (RDX) found to have a great level of ammonia; thus in a mp test there should be a characteristic odor.
Much more significantly a well shaped, clean crystal will react to diphenylamine with a vivid blue color.

Basically the questions I am trying to answer are:
1) What are the impurities?
2) What are the percentages of impurities?
3) Will the impurities affect the storage, sensitivity and initiation characteristics?

Apologies if I come across wrongly but I can see how the methods suggested can determine whether the sample is impure, but not shed much light on the above.

hissingnoise - 1-5-2011 at 08:44

I can prepare WFNA fairly easily, but getting my hands on (AC)2O is an altogether different matter.
As for Ledgard's tedious and dodgy tome - I wouldn't put a lot of trust therein!

IndependentBoffin - 1-5-2011 at 11:16

Quote: Originally posted by hissingnoise

I can prepare WFNA fairly easily, but getting my hands on (AC)2O is an altogether different matter.
As for Ledgard's tedious and dodgy tome - I wouldn't put a lot of trust therein!

What country are you in? I was able to buy acetic anhydride OTC in the UK.

Can acetic anhydride be conveniently prepared in a laboratory setting? I've read the wiki:

http://en.wikipedia.org/wiki/Acetic_anhydride

...but am unsure how easily the precursors and catalysts are obtained, what the costs are and how safe the process is.

Lots of typos in Ledgard's tome but is there anything factually incorrect or downright dangerous in it? I know for a fact some 100% kosher facilities use it as an energetics production reference.

Or are you hinting that it is possible to directly nitrate hexamine with 70% nitric acid, via a method not described in Ledgard's book?

hissingnoise - 2-5-2011 at 03:35

Quote:

I was able to buy acetic anhydride OTC in the UK.

Now that is interesting!
But the operative word here is "was" . . .
I tried about a year ago - even going so far as to converse with a H.O. apparatchik!
He didn't buy my cover story . . .

IndependentBoffin - 2-5-2011 at 05:23

Quote: Originally posted by hissingnoise

Quote:

I was able to buy acetic anhydride OTC in the UK.

Now that is interesting!
But the operative word here is "was" . . .
I tried about a year ago - even going so far as to converse with a H.O. apparatchik!
He didn't buy my cover story . . .

Is it now?

The acetic anhydride arrived as recently as a month ago. You can see from the picture the bottle is brand new and still pretty much full.

I also ordered various other (some may say) "dodgy" chemicals around the same time 35% hydrogen peroxide, 70% nitric acid, 98% sulphuric acid, glacial acetic acid, hexamine, acetone, sodium bicarbonate, alkalis, LP ammonium nitrate, etc.

Granted my first order from one supplier took about 3 months to arrive but it finally did. They kept giving an excuse that the glacial acetic acid was frozen and they had to order special drum heaters to heat it up and the whole order was delayed because of that, etc. I asked them to ship it separately but they didn't. So if you or anyone else has a dodgy rap sheet be aware that I suspect the supplier passes on details to HMG to run checks.

Send me a U2U if you want details of the supplier. And please don't order 25L of acetic anhydride, hexamine, AN and nitric acid in the same order, OK?

[Edited on 2-5-2011 by IndependentBoffin]

quicksilver - 2-5-2011 at 06:31

QUOTE:
"Basically the questions I am trying to answer are:
1) What are the impurities?
2) What are the percentages of impurities?
3) Will the impurities affect the storage, sensitivity and initiation characteristics?"

Lower nitrated products generally. Percentage depends on a great deal of variables HOWEVER, the fact that the technique uses lower levels of acid invites lower nitrated amines. The STANDARD Plant-level production technique is to use 1.50+ acid and a hexamine di-nitrate precursor (in US/UK-NATO plants, etc).
Impurity WOULD most definitely affect storage properties. Ammonia & formaldehyde, ad nausium..... would bring product to a shelf life of months instead of years. Technique for discernment is generally re-crystallization with USP grade acetone (no petroleum distillates): you want to see a clear 1mm size broken hex crystal similar to very clean table sugar. Lower nitrated products will often stay in the acetone unless evaporated or temp transition is extreme, then product appears as fine white/buff powder similar to chalk-like material (non-crystalline powder).

See studies done by G. Hale and Bachmann (sp?)

[Edited on 2-5-2011 by quicksilver]

hissingnoise - 2-5-2011 at 07:16

LP Chemicals was the last company I tried!
I'm not really that stuck for the anhydride, though - I find direct nitrolysis easy enough, although I hadda threatened runaway with hex tabs/RFNA, fairly recently.
Hexamine prepared from formalin and HN4OH seems less touchy - better purity, probably.
It's kind of ironic, though, that you can easily get a restricted chemical OTC but something simple like NH4NO3 is your bottleneck.
I have lbs of it lying around

IndependentBoffin - 2-5-2011 at 08:41

Quote: Originally posted by hissingnoise

LP Chemicals was the last company I tried!
I'm not really that stuck for the anhydride, though - I find direct nitrolysis easy enough, although I hadda threatened runaway with hex tabs/RFNA, fairly recently.
Hexamine prepared from formalin and HN4OH seems less touchy - better purity, probably.
It's kind of ironic, though, that you can easily get a restricted chemical OTC but something simple like NH4NO3 is your bottleneck.
I have lbs of it lying around

Yup I used those guys to get acetic anhydride. Didn't know you guys were so open about suppliers. The culture in other forums is to be very shy about these things.

Nah, I can get LR ammonium nitrate. Expensive, but pure.

The fertiliser sourced AN is for rocket fuel, which is a lot less touchy to impurities than HE. For HE (primary or secondary) only the purest stuff will do.

100g of solid rocket fuel sputtering (likely) or spontaneously combusting (unlikely) because of impurities is bad. 10g of HE going off prematurely because it is sensitised by an unknown contaminant is a bloody disaster.

Maniak - 2-5-2011 at 11:21

RDX prepared via procedures involving acetic anhydride may contain some partial acetoxy derivatives or even acetoxy terminated linear nitramines. Heating RDX in suspension in 50% acetic acid (or in diluted mother liquor resulting from Bachmann synthesis) to 95-100°C for >60 minutes will destroy most of these unwanted impurities leaving RDX and HMX nearly unaffected. RDX which is treated this way may still slightly smell like acetic acid (when stored in a closed container for months), but in my opinion there is no danger of decomposition.

You can try this heating in acetic acid and checking melting point before and after will give you valuable information as well as weight difference. Bachmann RDX after this stabilization usually possesses mp of >190°C due to some amount of HMX.

hissingnoise - 2-5-2011 at 12:03

Quote:

Yup I used those guys to get acetic anhydride. Didn't know you guys were so open about suppliers.

We're not!
Acquisitions failures we'll talk about but staying mum on successes is a cardinal point. :cool:

But seriously, your having a reg. company obviously makes things easier.
There's a plethora of threads here on ketene synthesis, that of acetyl chloride et al . . .
I still love the simplicity of hex/NA though!

holmes1880 - 21-6-2011 at 09:37

What the hell is going on with deflegration point of RDX? I can't find it anywhere! Every reference only gives its melting point of 202C. :mad:

UPDATE: 260C based on dis:

http://www.teledynerisi.com/products/0products_8td_page02.as...

[Edited on 21-6-2011 by holmes1880]

quicksilver - 21-6-2011 at 10:02

It's very possible that a deflagration point has independent variables. The elevation, available oxygen, the "type" of deflagartion (i.e. bulk, single crystal loose, compressed), point of flame contact, etc for an exacting number to be used with the same utility as a MP.

The WiZard is In - 21-6-2011 at 10:31

Quote: Originally posted by IndependentBoffin

If one were to prepare a small sample of RDX (about 10g) by the acetylation of hexamine to DAPT (3,7-Diacetly-1,3,5,7-tetraaza[3.3.1]bicyclononane) and then nitration with 70% nitric acid in the presence of glacial acetic acid, acetic anhydride and ammonium nitrate (scaled down from Ledgard, J. "Prepratory Manual of Explosives" method), what are the methods used to confirm the purity of the sample?

Explosives testing is out because it won't tell you if a sample is 90% or 99% RDX anyway. Also of interest is in ensuring there are no unstable secondary byproducts which may sensitise or decompose the otherwise relatively insensitive + stable RDX.

Ye old PATR-2700 Volume 9, 1980 devotes 45 pages (R120-146).
(Free DL.)

Sez - R 140. Modern analytically methods for RDX tend to stress
instrumental techniques.....

See also Volume 3 C 611-621.

Current Military Specifications for RDX

http://www.everyspec.com/MIL-SPECS/MIL+SPECS+(MIL-DTL)/MIL-DTL-398D_11163/

djh
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