[kriggy]

Hi there, Im doing an reaction sequence of diazotation and then forming diazosulfonate  (is it called that way?) R-N=N-SO₃^- using Na₂SO₃. The problem is that my starting material is very insoluble in water so the reaction doesnt proceed or I get only low yields with recovery of starting material (in the same mixture so further purification is needed).
Ive tried dissolving my SM in CH₃CN but after adding HCl it precipitated again :/
Is something like DMSO usable for diazotations? Im not sure but I think that most organic solvents will not dissolve NaNO₂ and / or Na₂SO₃ that is used after the diazotation.

Thanks for help

[opsomath]

I often use acetic acid as the solvent for the organic compound. Here's an example...we should have a Synthetic Page up for this sort of thing soon. It's ok to have some precipitate, the reaction is often a bit slushy.

https://docs.google.com/document/d/1eRmpeFrQAkupuAXPCjaVanfR6WKAJlrs2IWzKGZ0hVE/edit?usp=sharing

[Dan]

What about a mixture of water and MeCN?

Can you use tButyl nitrite instead of HCl/NaNO₂ for the diazotization? I've used that before for Sandmeyer reactions in the past.

[pgk]

1). SANDMEYER TYPE REACTION IN DIMETHYL SULFOXIDE
Organic Preparations and Procedures, 1(4], 221-224, (1969)
http://www.tandfonline.com/doi/abs/10.1080/00304946909458386?journalCode=uopp19#
2). What about a mixture of water and DMSO?

[kriggy]

Opsomath: I was thinking about it but sodium sulfite is not stable in acidic enviroment so I would need to use more molar amounts of sulfite thatn acetic acid and that would be huge amounts. It might be worth trying. Im following published procedure and I get some precipitate when replicating their work from ARKIVOC 2011 (ii) 127-136 bunt im trying to make a compound 3 (and then 4) where R=Cl.

Dan: I tried mixture (to be exact, dissolve in MeCN and then add water) but the SM precipitated anyway. I dont have my lab notebook with me but as far as I remember, the MeCN and water mixture gave me about 20% conversion and 5% other impurities, the rest is starting material so it might be way to go but I have no idea how to further improve it. I didnt try tButylNitrite, Im not sure if we have it in a lab but thats good idea. Is it soluble in organic solvents?

pgk: thans for article, I´ll read it as soon as I can

[Dan]

Yes tBu nitrite is organic soluble (and presumably insoluble in water). I used it for some Sandmeyer reactions in MeCN a while back. It might be a strategy worth investigating but I don't know if it will necessarily transfer to your reaction.

[kriggy]

Thanks, I will look into this option

[opsomath]

There's also nitrosonium tetrafluoroborate, which AFAIK can be used directly in some organic solvents. It's commercially available but has to be handled under nitrogen (I used a glove box). I don't have a prep on-hand though.

It has the advantage that it comes with a counterion included, so that you don't have to add BF3 or anything which could presumably screw with your sulfite nucleophile.