Partial nitrations?

[LibertyOrDeath]

As a non-chemist attempting to learn more about the key reactions involved in explosives manufacture, the issue of partial nitrations has been bugging me. I've been searching the web, this site, and looking through all of my books on explosives chemistry, but the answer is eluding me, so I'm hoping that one of the chemists here can enlighten me a bit or at least point me in the direction of what to read.

If this question is naive or stupid -- or if the answer is overly complex -- then please delete this thread (and hopefully not me along with it ;)), and I'll take that as a cue. On the other hand, maybe it will stimulate some interesting discussion, as is my hope.

With that out of the way, here's what I'm pondering:

Say you're nitrating erythritol. There's room for four nitro groups on the molecule, and your goal is to get tetranitrate rather than tri-, di-, or mononitrate. How can we be certain that the vast majority of the product is fully nitrated?

Of course I understand that properties such as melting point, solubility in various solvents, and even color can be affected by the degree of nitration. Certainly completely un-nitrated erythritol has entirely different properties from ETN. But I just don't know for a fact that erythritol TRInitrate has properties significantly different from those of TETRAnitrate. Can we be confident of such a thing? Perhaps erythritol trinitrate is also explosive but has less power.

It's my understanding that when creating a nitrating mixture, an excess of acids is used so that you have enough nitronium ions floating around to attack all sites available for nitration on all available molecules. Stirring increases the probability of contact between nitronium ions and sites on erythritol molecules that have yet to be nitrated. And I suppose that temperature control is used to limit competing reactions. Yet it's very difficult for a chemistry novice like me to understand, or even research, WHY a certain temperature range is most favorable to nitration, or HOW favorable it is to nitration over other reactions. So if I'm making ETN, I don't know if I'm making 99% tetranitrate, 80%, or 50% versus partially-nitrated erythritol. I suppose the same could be said for NG, MHN, etc.

Would anyone care to comment on this issue, even if it's just to point me to a good book? Thanks in advance for any help!

[nbk2000]

I'd not be too concerned about the ETN being Tri- instead of Tetra- nitrate, as the difference in VoD would only be a few hundred meters, I'm sure.

[Charles Owlen Picket]

I am not a chemist but I think I know what you are asking as I have thought about something similar. There is a GREAT old book entitled "The Pentaerythritols", Evelyn & Robert Barth, John Snow. Published by Rienhold in 1958....one edition. Worth finding! It outlines what can and cannot bind (with, in this case PETN or ETN) and what happens in terms of energetic and polymer chemistry.

It was not light reading for this old man. I had a undergrad textbook on organic chemistry available to follow up on some subjects (Chemistry, A Modular Science; Moore, Stanitski - a very good source).

With the subject you're after, there is an energetic noted as PEN as well as PETN. PEN is the trinitrate and can even be found in Ledgard's Preparatory Manual of Explosives! [See procedure 13-04]

Now, I don't trust Ledgard as his patent number are not accurate (I've searched quite a bit on some of his shit) but his research (on PEN) came from the Rohm & Hast Company (1969) who made explosives for industry during the 1960's. It seems that when you are dealing with complex polyols (esters) dropping one (tri/tetra) has virtually NO effect on VoD or even sensitivity for that matter. That is NOT the case with other materials (nitric amines for instance). So the specific material to be nitrated has a great bearing on this subject.

Check info on the nitration of Sorbitol, etc. If you drop from the hexanitrate to the tetranitrate, it still shoots well.
The influencing factors are time, temp and ratio of acid, polyol, & reaction modality. I hope I started you off in a productive direction. {It's early and I have to go to work.}

[Enkidu]

I don't want to type right now... so this will be brief.

Three types of nitrations.

C-NO2 = 'true' nitration, NO2 group called 'nitro'

With aromatic nitrations, partial to full nitration controlled by molar ratios of nitronium ion. Read up on electrophilic aromatic substitution.

O-NO2 = esterfication reaction, ONO2 called 'nitrate' (as in potassium nitrate, KONO2, ETNitrate).

With polyols, you generally get all or nothing, except in cases of extreme steric hindrance. Very few % partially nitrated compounds. Read up on equilibriums.

N-NO2 = an amide, N-NO2 called nitramine.

Not sure about nitramines; maybe someone else can tell you.

[hereno]

Its an equilibrium reaction as enkidu mentioned. Using a large molar excess of nitration acids will result in a higher proportion of fully nitrated polyol, but note that you will never get a 100% yield due to the equilibrium. But this doesnt matter as the lower nitrated derivatives are considerably more soluble then the fully nitrated ones thus a good water wash is all thats necessary to isolate your wanted product.

This is most clearly seen in nitrocellulose which cannot be washed free of the lower nitrated products as its a polymer, thats why nitrocellulose is graded on nitrogen percentage rather then nitrate groups.

[Alexires]

Liberty - I think that you will find that it is the nature of chemistry. It is impossible to have a 100% chemically pure substance. LR chemicals are very pure, but not perfectly so.

So to relate back to what you are asking, yes, there will be some other by products that you will never get rid off, but if what Enkidu is saying is correct, then I think that you can be fairly confident that your PETN is fairly pure, and that too much washing will be detrimental to your product (loss of product).