[Nescafe]

Hi,

I am hoping to convert Hbr salt of a alpha bromo acetophenone type of functionality I made to an azido using NaN3, do I have to worry about safety when NaN3 encounters HBr? I say this because I recall that mixing acids and NaN3 is a dangerous combination.

Thanks,

Nescafe.

[discodermolide]

Sodium azide and HBr will produce HN₃, which is a toxic very explosive compound.
What solvent are you going to use?
So yes you may well have a saftey issue.

[Nescafe]

I was going to do it in acetonitrile, that is what I usually do such reactions in. Problem is that if I desalt, then the material is unstable, so I have to do a few steps in one pot. Would I be able to get away with adding excess sodium bicarbonate? So basically my HBr salt + acetonitrile + excess sodium bicarb (solid) then at 0C add the sodium azide?

[discodermolide]

You may get away with that method.
Connect the gas outlet to a NaOH washer to trap any HN₃ that may be produced.

[Dan]

Is this an HBr salt of an amine (or similar) or is there actually free HBr in there?

The pKa of hydrazoic acid is 4.6, so provided your salt is less acidic than that, you should not form much HN₃.

[Nescafe]

It is a pyridinyl salt, so Pyridine-HBR

[discodermolide]

In the gas phase above NaN3 one can detect considerable amounts of HN3. Moisture and CO2 are enough.
So care needs to be taken here.

[Nescafe]

Hmm, not sure what to do, can I like stir it in dioxane sodium bicarbonate first then add the azide at 0C?

[discodermolide]

Why not stir NaN₃ and bicarbonate in that solvent and add the bromo compound dropwise. Don't keep the temp. too low otherwise the reaction may be slow, RT may be better?

[Nescafe]

Pretty good idea disco, so solid bicarb and azide in acetonitrile, then add the HBr salt of pyridine, would the bicarb even dissolve and do what it needs to though?

[discodermolide]

Doesn't need to dissolve, it will mop up any HBr all by itself.