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Author: Subject: phosphorus oxychloride (POCl3)
Vosoryx
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[*] posted on 16-3-2021 at 10:24


A few years ago I synthesized a small amount of POCl3, IIRC I planned on using it as a catalyst for something, clearly never got around to it and that experiment got lost.

I can't recall the exact procedure, but it involved passing chlorine gas over a mixture of Trisodium Phosphate and (I think?) activated carbon in a quartz tube heated to a few hundred degrees. The resulting mess of chemicals were condensed and then distilled, I had to do the reaction a few times to generate enough to distill as my quartz tubes are very small in diameter.

The exact procedure I got from here but all my chemistry books are on my old hard drive at home...

That reaction would only really work for small scale amounts, and I hate doing anything with chlorine gas.




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draculic acid69
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[*] posted on 16-3-2021 at 18:09


Quote: Originally posted by Elemental Phosphorus  
Quote: Originally posted by draculic acid69  
Can U not just buy p2o5 from China or something.they sell everything.


As far as I can tell, at least for Americans, it is available from various suppliers, even on ebay (but only as an ultra-pure analytical reagent), however it tends to be expensive:

https://www.ebay.com/itm/Phosphorus-Pentoxide-99-9999-Metals...

This is over a hundred bucks for 25 grams. However, if you make an account with firefox-fx.com (Firefox Fireworks) you can buy a pound of phosphorus pentoxide for $21.


A pound for $21, problem solved. U can make all the pocl3 or poly phosphoric acid you'd ever need.
This deal sounds like a logical choice.
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draculic acid69
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[*] posted on 16-3-2021 at 18:13


Quote: Originally posted by Vosoryx  
A few years ago I synthesized a small amount of POCl3, IIRC I planned on using it as a catalyst for something, clearly never got around to it and that experiment got lost.

I can't recall the exact procedure, but it involved passing chlorine gas over a mixture of Trisodium Phosphate and (I think?) activated carbon in a quartz tube heated to a few hundred degrees. The resulting mess of chemicals were condensed and then distilled, I had to do the reaction a few times to generate enough to distill as my quartz tubes are very small in diameter.

The exact procedure I got from here but all my chemistry books are on my old hard drive at home...

That reaction would only really work for small scale amounts, and I hate doing anything with chlorine gas.


This also sounds doable for the more adventurous members
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zed
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[*] posted on 17-3-2021 at 06:45


Ummm. Things get lost. This has been on the site for years. Once upon a time, a poster here wrote a book.

It's a good book. Not cheap... About 70-80 Bucks in Paperback. Gotta search for it too! POCl3 prep is included. Though Chemplayer's/Querty Querty's Acetyl Chloride prep, and The Benzoyl Chloride Chlorination are very useful, sometimes you gotta have the fancy stuff... PCl3, PCl5, POCl3, Oxalyl Chloride.

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See Lerner, Leonid (2011). Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling. Boca Raton, Florida: CRC Press. pp. 169–177. ISBN 9781439813126. PDF available from libgen.


Quote:

19.3.1 Preparation from P2O5

The best reaction vessel for this preparation is a test tube with a quickfit joint, a capacity of at least 100 mL, and at least 22 mm in diameter. If this is not available, a 100-mL, single-neck flask can be used instead with a slight loss of yield. Scaling the reaction requires proportionally larger vessels.

First, 35.1 g (0.25 mol) of phosphorus pentoxide is rapidly introduced into the reaction vessel, ensuring that as little atmospheric moisture as possible reacts with the P2O5, as it subsequently generates HCl and HPO3, which attacks the glass. The transfer is best done by inverting a powder funnel inserted into the reaction vessel, over the mouth of the reagent bottle, and tilting until approximately the right amount of reagent is transferred into the flask. Next, 34 g (0.58 mol) of finely ground and thoroughly desiccated (1 h at 250°C) NaCl is added, and the reagents thoroughly mixed. The approximately twofold excess of NaCl improves the yield by about 10%. Finally, about 10 g NaCl is poured in a layer on top of the mixture, which serves to convert unreacted P2O5 subliming from the reaction zone (bp 360°C). The reaction vessel is placed in an air oven and connected to a bend leading through a Liebig condenser to a receiver flask immersed in cold water. The outlet from the flask is vented through a CaCl2 protection tube with a bubbler optionally attached for observation of reaction progress.

The oven is rapidly heated to 270°C, from where the temperature is raised more slowly to 450°C at about 65°C/h. A distillation conducted more rapidly than this will serve both to reduce yield by excessive sublimation of P2O5, and increase the possibility of the reagent vessel bursting due to excessive buildup of HCl and POCl3 pressure inside the reactor, as these do not have sufficient time to percolate through the viscous sodium metaphosphate medium (the reagents liquefy during the reaction). About 8.2 g (0.053 mol) POCl3 collects in the receiver at the end of the reaction while the reactor tube loses 9.3 g (the difference is due to losses in the distillation setup), corresponding to a yield of 76% (86% with respect to reactor weight loss) based on P2O5.


[Edited on 3-7-2020 by DavidJR]


[Edited on 17-3-2021 by zed]
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FrenchChemist
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[*] posted on 26-4-2021 at 23:19


Good preparation of POCl3, I did mine with PCl3 which made the process a bit easier.

It is known that having access to pcl3 - pocl3 synthesis may seem strange and wasteful but I did it on a very small scale purely experimental.
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