Can Phosphorus Trichloride be made by simply reacting red phosphorus with chlorine gas? And if so what would be the best procedure? Would adding chlorine bleach to Hcl and then running the gas through tubes to the red phosphorus do it?

UTFSE (not totse's).

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From The Hive:
hypo
(Hive Bee)
05-20-01 14:01
No 195821
Synthesis of PCl3/PCl5 not _that_ easy. Reply

I'm transcribing a story i was told, please excuse any inaccuracies:

"""
I remember reading in Inorganic Synthesis I about a pretty complicated aparatus for making PCl3 out of red P and Cl2 and in Inorganic Synthesis III (or the other way round) about an even more complicated apparatus for making PCl5 out of PCl3. Yet several people told me making PCl3/PCl5 is a simple matter of passing chlorine gas over red P. So i thought: just try it!

Cl2 was produced by dropping conc H2SO4 on 15% NaOCl. It was piped into a rb flask containing a spatula of red P. Excess gas was piped into a 500ml cylinder filled with 20% NaOH. When the Cl2 hit the phosphorus, the thing ignited, filling the whole flask with white smoke. Production of Cl2 was suspended until one could see anything else than smoke. White powder (PCl5??) had resublimed in the whole flask and the outgoing tubing. On the bottom of the flask, there was a big chunk of white powder covering the unreacted phosphorus. Further passing of Cl2 gave no effect. The aparatus was dismantled carefully and inspected. Out of the tubing some dry powder could be rescued, which reacted violently with water forming a gas. The powder in the flask was "wet" (PCl3??). It too did react violently with water but left a little white residue, which did NOT react with water (P2O5, whatever...).

A total fuckup . And btw: the NaOH trap didn't work as well as expected.

I think i will lookup that inorganic synthesis text again. But as far as i remember the method was too involved.
"""

Hm... I'll leave that uncommented..




halfapint
(Hive Bee)
05-20-01 18:29
No 195852
Re: Synthesis of PCl3/PCl5 not _that_ easy. Reply

I think there is a good possibility here that unconsidered water was the root of the problem, as it is in so many other cases. Water or its vapor is going to end up as phosphoric acid in this system. Coming from the chlorine generator, I failed to see a mention of any provisions for drying, though a CaCl2 drying tube could have been easily inserted into that line. Otherwise, had solid hypochlorite been used with concentrated sulfuric acid, rather than a water solution, water would have had little chance of contaminating the reaction.

The white smoke and powder described was probably P2O5, from the phosphorus burning in the residual air inside the vessel. P2O5, the anhydride of phosphoric acid, one of the thirstiest substances known, clumped on the phosphoric acid formed on the surface of the phosphorus. That phosphoric acid had locked up all the water in the flask.

Wet chlorine coming in contact with the phosphorus provided the ignition, but the phosphorus mainly burned with oxygen. To truly test the reaction of phosphorus with chlorine, dry the chlorine, dessicate the phosphorus, and if possible flush the air out with (dry) nitrogen or helium before introducing chlorine.
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Turning science fact into <<science fiction>>



terbium
(Hive Addict)
05-20-01 21:33
No 195880
Re: Synthesis of PCl3/PCl5 not _that_ easy. Reply

Like making white phosphorous, this is probably something that is not a big deal when done in an industrial setting where you are going to make a ton a day but quite a bit of a hassle for someone who wants only a few hundred grams.

I would guess that this needs to be done in a vapour phase by combining a stream of phosphorous vapour in a nitrogen carrier with another stream of chlorine in nitrogen.



darius
(Stranger)
05-20-01 22:23
No 195891
Re: Synthesis of PCl3/PCl5 not _that_ easy. Reply

yeah that can be difficult, another problem you might have had is with the NaOCl. along with freeing up the chlorine, you also release O, this bonds very readily with P. there are some other things you could try though, i haven't though, but you might wanna try using HCl acidand seeing if you can release the Cl off of that, that would at least help by limiting the number of other elements involved. also if you can try to execute the game plan under a vacuum, if you can't don't worry about it. but try something like NH3 and HCl, maybe that would work, it would leave you with 2NH4 and Cl2 (i think, i'm just guessing, you really oughta check that)

take it easy
darius



Chromic
(Hive Addict)
05-20-01 22:56
No 195896
Re: Synthesis of PCl3/PCl5 not _that_ easy. Reply

On the chlorine exhaust: might a push-pull device loaded with sodium thiosulfate work better to trap the free chlorine?



hypo
(Hive Bee)
05-21-01 09:56
No 195960
Re: Synthesis of PCl3/PCl5 not _that_ easy. Reply

Thanx for the great replys! The chemist right now has no way to produce pure Cl2, but the day will come...

In case you wonder how the Inorganic Syntheses people do it: They pass Cl2 through conc H2SO4 and then into a flask with a refluxing PCl3/redP mixture (They have PCl3 to start with!). Thus they avoid formation of PCl5 and contact of the redP with O2. The whole aparatus is protected with a P2O5 drying tube.

Hmm..

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