[wildfyr]

Hi everyone,

Normally to dry a solid I will try one of 3 approaches:
1. Dissolve it in a fairly dry solvent, then add sieves or another drying agent, then decant and rotovap it down to remove the solvent.
2. Put it in an RBF under vacuum, then put a of flask P₂O₅ between the compound and the pump. This has always worked magnificently.
3. Put it under hi-vac and heat it for a few days

I have a branched polymer with -OH terminal groups that I want to react with acryloyl chloride. The packaging says there may be leftover water, and  the material is somewhat hygroscopic. Since polymers are not well suited to the solvent+sieves trick or the hivac+heat method, and I don't have P₂O5₅, I was wondering if I could substitute KOH powder. I figured the drying mechanism is just that P₂O5₅ is really really hygroscopic and the equilibrium sucks all the water out of the desired compound. KOH is at least as hygroscopic, and should act the same way. Thoughts?

[pgk]

If your OH-terminated polymer is dissolved in warm toluene or xylene, you can remove water by azeotropy in a reactor equipped with a Dean Stark condenser, followed by solvent removing under vacuum and then, continue the acylation in the same reactor. Alternatively, you can use the rotary but the solvent removing will be long.
Toluene azeotrope 84.5 oC
Xylenes mixture azeotrope ≈ 94.5 oC

[Borek]

KOH is at least as hygroscopic, and should act the same way. Thoughts?

Nope, check for example here. P₂O₅ is much, much more effective.

Doesn't mean KOH is useless, it is just another league.

[wildfyr]

Thanks Borek, that is a terrific reference! Good way of thinking about the problem and googling to find the right answer.

I've ordered P₂O₅ (dang its cheap! 0.5 kg $24). My polymer is poorly soluble in toluene so I don't think the toluene azeotrope method will work. I'm sure I can pull that trick out of the hat on another day though, so thanks.

[Borek]

Thanks Borek, that is a terrific reference!

Just a lucky find, I was almost sure P₂O₅ is way better than KOH and that was the first reasonable hit that confirmed my memory.

[rolnor]

When working with carbohydrates I usually dissolve/suspend the material in DMF or pyridine and put on the rotavapor.

[wildfyr]

Your pump must stink to high heaven rolnor. Pyridine and the trace amines of DMF never come out of those rubber seals.
Also, does your rotovap really get all the solvent removed?

For my case, if there was leftover DMF or pyridine it wouldn't affect the acrylation reaction I guess.

[phth]

Thanks Borek, that is a terrific reference! Good way of thinking about the problem and googling to find the right answer.

I've ordered P₂O₅ (dang its cheap! 0.5 kg $24). My polymer is poorly soluble in toluene so I don't think the toluene azeotrope method will work. I'm sure I can pull that trick out of the hat on another day though, so thanks.

Others as well.  What doesn't form an azeotrope with water .  P2O5 is dank by the way https://www.youtube.com/watch?v=ccPcfYQnmVw

[wildfyr]

Another question on this topic: When my acryloyl chloride gets here, I am going to open it, and it probably won't have a septum on it if bottles from grad school are any indication. This will obviously cause both instant and gradual hydrolysis.

Here comes the clever idea: instead of transferring it to a shlenk flask (and even that would suffer the same problem, albeit more slowly) and redistilling it every time I need to use it, I could add a small amount of thionyl chloride. This will both consume water, and convert acrylic acid back to acrloyl chloride. I will also probably have to bleed it every once in a while to let off pressure, but that shouldn't be bad as long as I don't let too much water get in.

 I am unlikely to use this reagent in a reaction which cares about SO2, and HCl is produced by acryloyl chloride anyways. I'm not worried about any alcohols being converted to alkyl halides since they will much more quickly react with the acyl chlorides. What do yall think?

[pgk]

It’s better to avoid this:
1. The uncontrolled generation of SO2 can cause an explosion in a closed container, at any unpredictable moment. On the other hand, you cannot leave the container open because the contained mixture is teargas and has awful odor. Besides, atmospheric humidity will penetrate therein.
2. The reaction is very slow without (even a slight) heating.
3. The co-generated HCl (in addition to the contained amount of HCl from hydrolysis of acryloyl chloride) will inhibit the acylation of the next step.