There are some compounds which are much easier to obtain as X-Cl than (say) X-ONO2. I've been wondering about various methods to cleanly make the transformation without destroying X (say something with CHNO in it). I'm assuming that the stuff to be modified is actually a salt i.e. X is effectively a base and H-Cl makes the combination approximately neutral.

Precipitate? The most common thing I know of would be AgNO3 + XCl -> XNO3 + AgCl \|/ (downarrow).
Effective but expensive.

Remove by sparging/distillation? HCl is considerably more volatile than HNO3, but how much more volatile? My handy references (Merck, CRH) have various pressure, BP, etc. figures but none that I can convert to congruent units. I'd assume that warming a pot of (stoichiometric) HNO3 + XCL and bubbling a lot of air through it (warm it? which way does the differential go?) would remove more HCl than HNO3 but how much?

Remove by oxidation? Cl- -> Cl is higher potential than O2-- -> O-- + O. It's lower than S2O8-- -> S2O7 + O, so that might work, but then one would (say) add BaOH to remove H2SO4.

Any bright ideas or places to look?

Does your x stand for a metal or for an organic functional group?

>>Does your x stand for a metal or for an organic functional group?

Sorry to be unclear - it's organic and fairly small ( something with a couple of Cs, a dash of N, and H all around ).
Any of the small alkaline C-N or C=N things. C -3- N is a little toxic to play with. I'm being a bit vague, I know, but I've run into this problem with a couple of compounds. Not something larger like an alkaloid. The thing which is really annoying is (being out of school and working) it's hard to get to (and into) a library with the Big Solubility References. Thanks!

Are you trying to convert a clorine into a nitro group? IIRC the clorine binds stronger to carbon - hard task.

If it is about x-hydrochloride into x-nitrate like in HDN or MMAN, you could have a look at the MMAN thread, into Megas chemlab, or on some member's site (Mr Cool, Aleng, ??? forgot where sorry) where I remember the route went via MMA-HCl.

Good to hear it is no alkaloid. -ONO2 is not going to help you there anyway. I would rather try to attach two acetyl groups to *something* , or get a benzyl group into the XYZ-methylester.... wasn't that one via P2P or did I smoke too much?

Organic chemistry has its signs!

X is halogen atom.
R is an alyphatic (non - aromatic) hydrocarbon.
Ar is aromatic one.

So you mean R-X to R-ONO2 - which has been discussed.

Oops - working with computers has made me forget my chemistry. What's the abbreviation for a group with heteroatoms? And what needs to be removed is an HCl which is ionically bound to the alkaline N.
(Hides under chair)
A small (2g) trial of ammonium peroxysulfate + HNO3 + the salt --> a significant amount of Cl2
The HNO3 -should- have been stoichiometric + a few % to have the H+ consumed by the peroxide oxidizing Cl- to Cl. It took a tiny bit of MnO2 to kick it off. Now to get rid of NH4HSO4..
Still, I would really like to do this without such powerful oxidizers. I fear that scaled up or contaminated
with the wrong things the oxidizers might go after the substrate.