[Reddart]

I was wondering if there would be any problem using THF with a diazonium salt? I am reacting somewhat hydrophobic aryl diazonium salts with very hydrophobic arylamines, so the standard aqueous acid conditions don't work. I have had some success AcCN for the diazonium salt formation, and adding it to NMP/pyridine (to buffer the pH), but there seems to be a slow decomposition reaction with NMP lowering the yield, and AcCN is a poor solvent for the substrate, though it is good for the N2+ salt.

I'm going to try THF, but I just wanted to see if there was any consensus on THF, or other non traditional organic solvents for diazonium coupling reactions.

A phase transfer system might potentially work given the polarities as well. I am trying to find some literature on that.

[kriggy]

Are you making azo compound or using diazonium as a leaving group in some kind of coupling?

I did some work with poorly soluble diazonium salts and used mixture of organic solvent and water, I think it was THF-water. Also, high dilution also worked to make it soluble.

[zarhym]

I would suggest using tert-Butyl nitrite in the formation of diazonium salt. By doing so in presence of BF3 Et2O, you will end up having ArN2+BF4 salt. By changing the anion, this diazonium salt may have better solubility in traditional organic solvents or even stable enough to be isolated for the coupling reaction.

Here is the paper you will find helpful about this idea.
https://pubs.acs.org/doi/pdf/10.1021/jo01323a048

[opsomath]

You can also precipitate your diazo salt using NaBF4 or NaPF6 from cold water. These isolated salts are not hazardous in general. Don't know if that helps you with your solvent problem, since you seem to need a more nonpolar solvent that will still dissolve the diazonium salt. However, I came here to suggest ACN, which has always worked brilliantly for me. Is your amine really not soluble in it? Perhaps you could use ACN even if not everything dissolves at first, and let everything mix together until the reaction was complete?

These guys do it in the solid phase: https://onlinelibrary.wiley.com/doi/abs/10.1002/1521-3765(20020315)8:6%3C1395::AID-CHEM1395%3E3.0.CO;2-L
although when I tried that reaction, it was long and tedious to do in a mortar and pestle.

DMSO reduces diazo salts, btw. You probably know that, but just thought I'd put it out there.

[wildfyr]

Tetraphenylborate salts are the king of crashing stuff out of water, and they are very not-explody or HF forming.

Sodium tetraphenylborate is pretty water soluble, but when it salts with something that isn't sodium everything tends to fall out. Even the potassium salt is poorly water soluble (most unusual).

[opsomath]

For at least one highly electron-deficient diazonium salt I made, it was reduced by tetraphenylborate in solution with lots of bubbling and black carbon forming. Might not be a general problem -  FYI!