I will need to dry a small amount of white P just prior to its use. I store my white P under water. Below is my plan for doing this. Please
critique this plan. If you know a better way please explain:
Drying of the White Phosphorus
The phosphorus is currently stored under water. Any entrained water must be removed prior to the time of use.
1. Place ~ 25ml of acetone in a 50ml Erlenmeyer flask.
2. Add ~1g of P2O5. Cork and swirl.
3. Pre-weigh the Erlenmeyer flask with the acetone, P2O5, and cork.
4. Cool the phosphorus in water to 5-10°C.
5. Remove ~2g of phosphorus, pat it dry on a paper towel, and place it in the Erlenmeyer flask.
6. Reweigh the flask and record the weight of phosphorus added.
7. Swirl the flask and set aside for an hour with occasional swirling
gdflp - 7-2-2015 at 14:04
The only possible issue I see with this plan is that the phosphorus could ignite as you are taking it out of the acetone. If that was the case, then
you could get quite a surprise as the acetone ignited. As long as you're prepared for this, I think that it should work fine. Would drying the
phosphorus with concentrated sulfuric acid, then rinsing a few times in a dry organic solvent to remove the excess sulfuric acid be feasible? A
combination of the two might work well, as the sulfuric acid could remove most of the water, while the phosphorus pentoxide could remove the last
traces. Just a thought.Magpie - 7-2-2015 at 14:08
I will be transferring the P directly from the acetone to 100 mls of chloroform, so it will not have a chance to heat up. Bert - 7-2-2015 at 14:26
FENIAN FIRE!!!
Put a drop of the white P solution on something like a piece of paper- Leave on a fireproof surface. Wait for the solvent to evaporate...
[Edited on 7-2-2015 by Bert]Magpie - 7-2-2015 at 14:35
The basis of my method is that P does not react with nor dissolve in acetone.Bert - 7-2-2015 at 16:25
But it DOES dissolve in chloroform, about 1g:40ml.
I understand the acetone should not dissolve the P. But be careful about any little splashes of the chloroform solution, white P in carbon disulfide
or chloroform was used as a sabotage incendiary mixture. Casualy pour it on something, walk away. A bit later there is a white P fueled fire.Hawkguy - 7-2-2015 at 17:11
Purge the flask with the WP using Carbon Dioxide. That should prevent whatever. Magpie - 7-2-2015 at 17:29
But it DOES dissolve in chloroform, about 1g:40ml.
Yes, that is my purpose for using chloroform in the synthesis to follow.Dan Vizine - 8-2-2015 at 15:27
I'd simply put the P in the CHCL3 and use azeotropic distillation (with a Dean-stark that returns the BOTTOM layer).
Protect from light!. I haven't looked it up in some time, but the heating alone shouldn't cause much change.
Where applicable, azeotropic drying is the method of choice for economy and, often, efficiency.
Lots of solvents have immiscible water azeotropes,.... methylene chloride, chloroform, toluene, xylene, and many more.
[Edited on 8-2-2015 by Dan Vizine]Magpie - 8-2-2015 at 15:59
Dan Vizine:
That does look like a good way to remove water. So I should keep distilling until the bp rises to that of pure CHCl3, correct? Hennig Brand - 8-2-2015 at 19:23
How about putting the wet sample of P in a drying tube and passing a stream of inert gas through until dry (if you have access to bottled inert gas it
should dry very fast). Or, maybe generate an appropriate gas and collect it using a pneumatic trough or some other apparatus. The P sample to be dried
could be placed in the vessel with the gas along with a suitable desiccant. I suppose for that matter the P could be stored in inert gas as well.Oscilllator - 8-2-2015 at 20:41
Here's what I think you should do:
-Place the phosphorous in a 2-necked flask along with some acetone or other low-boiling water miscible solvent. One neck of the flask should have a
vacuum take-off adapter, and the other should have an addition funnel
-Using a vacuum pump, evaporate off the acetone/water, leaving the dry phosphorous behind. Then turn the vacuum off and open the addition funnel. The
chloroform should be sucked sown by the residual vacuum to cover the phosphorous, without the phosphorous ever having been exposed to air.
This method has the advantage that everything happens in one flask, and the phosphorous never gets the chance to ignite, since it is always either wet
or covered with a liquid.Hennig Brand - 8-2-2015 at 20:48
"Purification of Laboratory Chemicals" simply says to dry under vacuum.macckone - 8-2-2015 at 22:21
Under vacuum sounds safer, no oxygen.Magpie - 9-2-2015 at 09:18
You guys are coming up with some good ideas. Thanks.
