sylla - 14-9-2003 at 10:37
could somebody explain me why for some synthesis, 'direct' nitration is not possible ? I've seen that for a large amount of reaction, a
mix of H2SO4 and HNO3 is used. Why not only HNO3 like for the RDX ? Which reaction takes place ?
Thanx for your answer(s) 
vulture - 14-9-2003 at 10:53
RDX is not an aromatic compound, while most other explosives tend to be aromatic compounds.
The precursor of RDX is reactive enough for direct nitration, but most aromatics aren't. They need the NO2+ ion to be nitrated succesfully, which
can only be produced by a mixture of H2SO4 and HNO3:
HNO<sub>3</sub> + 2H<sub>2</sub> SO<sub>4</sub> ----> H<sub>3</sub>O<sup>+</sup> +
NO<sub>2</sub><sup>+</sup> + 2HSO<sub>4</sub><sup>-</sup>
sylla - 14-9-2003 at 11:02
thx for your answer vulture :]
palpy - 14-9-2003 at 11:58
At first, i would slightly disagree with vulture: there are tons of nitric esters, nitramines,nitrosamines, nitroalka(e)nes, nitrates etc. that are
definitely not aromatic.
In fact, i'd say, only TNT and maybe Hexyl are vastly used these days (TNF and picrates belong to the past)
As for the nitration:
The problem is, that you need the HNO3 to give you NO2. That means you want the nitric acid to ACT LIKE A BASE! For this you need an acid STRONGER
than HNO3 (see the formula by vulture). That's what the sulfuric acid is used for. And what's more, the concentrated H2SO4 binds the water
(which is a byproduct of nitration), thus improving the equilibrium.
NO2 is an electrophile! That's why aromatics and alcohols are so easily nitrated.
I suppose you mean treating hexamine with fuming nitric acid for the RDX synth.
This is not really a nitration, but rather NITROLYSIS, and I can assure you, that the reaction mechanism is very complicated.
So you can't compare this with other (REAL) nitrations.
Hope I helped
vulture - 14-9-2003 at 12:09
You're right. I was oversimplifying a bit.