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Author: Subject: Phosphorus trichloride
killswitch
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Phosphorus trichloride

I have been trying to devise a hobbyist method for producing this substance for some time now. In my experience, it has proven impossible to purchase it due to its status as a chemical weapons precursor.

I've considered the problem at length and ask for help in reviewing and/or critiquing the method I've arrived at below.

• First, the assembly is purged with nitrogen. Then, powdered calcium hypochlorite (pool supply grade) is poured into a solution of pool-supply muriatic acid. This is done in a three-necked flask or similar sealed container.

• A feed tube of glass or teflon passes from the chlorine cell to a sealed container of concentrated sulfuric acid. The feed tube passes underneath the surface of the acid to ensure drying of the gas. A second feed tube near the top of the cell allows the chlorine to exit the drying cell.

• The third cell contains powdered red phosphorus. Since this is the actual production step, I might just buy it from China rather than scrape it off of matchboxes.

• The phosphorus cell will be significantly lower in elevation than the preceding cells to help concentrate the chlorine gas in lieu of anything more sophisticated, and will be composed of glass rather than teflon so as to withstand heating.

• The phosphorus/chlorine cell is heated until the red phosphorus rearranges to white, at which point oxidation via the gaseous chlorine should commence and continue until the chlorine is exhausted.

Now, this is merely an outline. I haven't done any calculations or started putting anything together. If there are any flaws in this setup (or if there is a more efficient setup) I'd appreciate knowing it.

As for specifics, I would like to know how best to put together such a setup that would not explode or burst. Quantities would also be helpful.

And lastly, I need to know more about the final step. Is sustained heating required? What temperature is necessary to minimize pentachloride formation?
• simba
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Some time ago I made a thread about making POCl3 (phosphorus oxychloride) at home, where someone posted an interesting paper about making POCl3 by heating phosphorus pentoxide with table salt at 250 ºC or so, where it also said that along with POCl3, a small fraction o PCl3 is also generated from the reduction of POCl3 by the iron from the metal container used to carry out the reaction (the reaction can't be done in glass container).

I think reduction of POCl3 could be a more suitable way to make PCl3 at home. Phosphorus pentoxide isn't controlled so can be easily bought also.
AndersHoveland
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Phosphorous trichloride is a volatile liquid that gives off extremely poisonous fumes. The mechanism of toxicity is similar to carbon monoxide, and the fumes from PCl3 are very much more poisonous than the chlorine gas used to make it. For this reason working with PCl3 can be very hazardous. I recommend you NOT try to make this, especially if you are an amateur hobbyist.

To make PCl3, phosphorous is reacted with chlorine. But excess chlorine will oxidize the PCl3 to PCl5. For best yields, it is important that the chlorine be free from moisture, this is usually done by passing the gas through porous CaCl2 powder that has been baked dry.

Red phosphorous spontaneously ignites in chlorine gas (it also ignites in bromine vapor).

[Edited on 7-5-2012 by AndersHoveland]
Lambda-Eyde
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 Quote: Originally posted by simba Some time ago I made a thread about making POCl3 (phosphorus oxychloride) at home, where someone posted an interesting paper about making POCl3 by heating phosphorus pentoxide with table salt at 250 ºC or so, where it also said that along with POCl3, a small fraction o PCl3 is also generated from the reduction of POCl3 by the iron from the metal container used to carry out the reaction (the reaction can't be done in glass container).

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simba
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Quote: Originally posted by Lambda-Eyde
 Quote: Originally posted by simba Some time ago I made a thread about making POCl3 (phosphorus oxychloride) at home, where someone posted an interesting paper about making POCl3 by heating phosphorus pentoxide with table salt at 250 ºC or so, where it also said that along with POCl3, a small fraction o PCl3 is also generated from the reduction of POCl3 by the iron from the metal container used to carry out the reaction (the reaction can't be done in glass container).

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yes, thats it.
AndersHoveland
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Sulfur dichloride can often be used in place of PCl3 as a regent in organic chemistry. Another common regent for this purpose is benzene chlorosulfonate.
killswitch
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I'm trying to make triethyl phosphite, so I need the phosphorus chloride rather than the sulfur chloride
killswitch
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Can phosphorus pentoxide be heated in the presence of chlorine to produce phosphorus chlorides?
woelen

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If you have access to red P, then you could make PBr3. The latter is more easily made than PCl3. With PBr3 you can also make the organic phosphite you want to make. I have written a web page about making PBr3. Have a look at this thread for more info:

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thanos thanatos
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 Quote: Originally posted by simba Some time ago I made a thread about making POCl3 (phosphorus oxychloride) at home, where someone posted an interesting paper about making POCl3 by heating phosphorus pentoxide with table salt at 250 ºC or so, where it also said that along with POCl3, a small fraction o PCl3 is also generated from the reduction of POCl3 by the iron from the metal container used to carry out the reaction (the reaction can't be done in glass container). I think reduction of POCl3 could be a more suitable way to make PCl3 at home. Phosphorus pentoxide isn't controlled so can be easily bought also.

Why can't it be done in a glass container, such as a quartz tube? The paper this idea comes from discussed generating POF3 and PF3, which would certainly be problematic in a glass vessel (as it generates fluorine gas as an intermediate). But if you're limiting yourself to chlorides, why would glass or quartz be a problem?
Lambda-Eyde
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Because phosphorus pentoxide itself will etch glass at these temperatures.

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Rogeryermaw
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i have looked and looked and looked but i can't find it anymore. i copied the synthesis a long time back for my notes but i will not publish it without the writer's consent. there is a simple and elegant home chemist level synthesis for PCl3 written by garage chemist complete with pictures and a detailed write up. u2u him for instructions. i believe it is in german (possibly dutch, can't remember now. translated it long ago). basically it consisted of a flask charged with white phosphorus and fitted with a reflux condenser. two additional gas generators were used. the first using a carbonate and HCl to produce CO2 which was led through the second gas generator whose purpose was to produce chlorine by reacting TCCA with HCl. the gases from these generators was dried in a washing bottle containing concentrated H2SO4. after flushing the reaction flask with CO2 (at which point CO2 production is minimal or stopped altogether) chlorine production begins (extremely slowly). there was described a violent exothermic reaction with bumping and sloshing, but crude PCl3 is produced. one must stop production of chlorine gas before the consumption of all the P4 to reduce the chance of PCl5. afterwards, distill the crude product.

the extreme toxicity of PCl3 has been mentioned here. do not discount that warning. efficient fume hood only.
plastics
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 Quote: Originally posted by Rogeryermaw i have looked and looked and looked but i can't find it anymore. i copied the synthesis a long time back for my notes but i will not publish it without the writer's consent. there is a simple and elegant home chemist level synthesis for PCl3 written by garage chemist complete with pictures and a detailed write up. u2u him for instructions. i believe it is in german (possibly dutch, can't remember now. translated it long ago). basically it consisted of a flask charged with white phosphorus and fitted with a reflux condenser. two additional gas generators were used. the first using a carbonate and HCl to produce CO2 which was led through the second gas generator whose purpose was to produce chlorine by reacting TCCA with HCl. the gases from these generators was dried in a washing bottle containing concentrated H2SO4. after flushing the reaction flask with CO2 (at which point CO2 production is minimal or stopped altogether) chlorine production begins (extremely slowly). there was described a violent exothermic reaction with bumping and sloshing, but crude PCl3 is produced. one must stop production of chlorine gas before the consumption of all the P4 to reduce the chance of PCl5. afterwards, distill the crude product. the extreme toxicity of PCl3 has been mentioned here. do not discount that warning. efficient fume hood only.

http://www.versuchschemie.de/topic,5775,-Phosphortrichlorid....
Rogeryermaw
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that's the one. makes me wonder if it was written by garage chemist. i did get the link from one of his posts though, and i know he frequents versuchschemie.de

the method, while requiring some expensive glass (especially the washing bottle), is well within the reach of the home chemist.
Lambda-Eyde
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Stefan would be garage chemist, yes. He also posted a synth of PCl<sub>5</sub> on this forum IIRC. I'll look it up.

Edit: At least I found the topic at Versuchschemie: http://www.versuchschemie.de/topic,8040,-Herstellung+von+Pho...

But I could have sworn I've seen it here on SM, too.

[Edited on 10-9-2012 by Lambda-Eyde]

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Rogeryermaw
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man, stefan/garage chemist has done some amazing work. did you read at the bottom where he proposes the synthesis of phosphoryl chloride from the PCl5 using either H2SO4 or Na2CO3? awesome!
Lambda-Eyde
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The route with Na<sub>2</sub>CO<sub>3</sub> isn't all that awesome - phosgene as a byproduct? No thanks!

[Edited on 10-9-2012 by Lambda-Eyde]

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S.C. Wack
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Phosgene can be used to make POCl3 from phosphate, at an easy temperature in a tube furnace, so a stream of it is not entirely inconvenient.

"You're going to be all right, kid...Everything's under control." Yossarian, to Snowden
Rogeryermaw
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 Quote: Originally posted by Lambda-Eyde The route with Na2CO3 isn't all that awesome - phosgene as a byproduct? No thanks! [Edited on 10-9-2012 by Lambda-Eyde]

true, but it would seem like the easiest method since the reaction products are a gas, a liquid and a solid. should make for easier separation than to distill POCl3 from chlorosulfonic acid. good fume hood should keep you safe.
Yamato71
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The Vogel synthesis of phosphorus tribromide (5th ed. pp 458-459) involves the dropwise addition of bromine to a vigorously stirred suspension of red P in carbon tetrachloride followed by fractional distillation. I've seen phosphorus trichloride generated in a similar manner by bubbling dry chlorine through or dripping liquified chlorine into the same suspension. IIRC, dichloromethane or chloroform can be substituted for CCl4 since both will react with excess Cl2 to form CCl4 and HCl. A dry ice/acetone condenser is set up for reflux to condense any escaping chlorine or CCl4 vapor and return it to the reaction flask. The reaction is complete when the suspended RP is consumed. Fractional distillation is employed to isolate the product from the solvent. Any formed phosphorus pentachloride will be precipitated as a white to yellow solid in the reaction flask. Filter this out and rinse with fresh CCl4 as this is a very useful chlorinating agent, especially for generating acyl chlorides from carboxylic acids. For example, when 2 equivalents of dry PCl5 are shaken with 1 equivalent of dry oxalic acid, the mixture liquifies into crude oxallyl chloride.

[Edited on 5-12-2012 by Yamato71]
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Can you produces PCl3 by reducing PCl5 with red phosphorus say in CCl4 solution?

How do you seperate PCl3 from CCl4 since the the former boils 76.1 and the later 76.7 C?

In the presence of excess red phosphorus could you chlorinate it to PCl3 in the dark (temperature will be limited by the reflux temperature of CH2Cl2) to limit chlorination of the solvent?

Can you use the solution of PCl3 in CCl4 directly in you intended reaction?

My interest in this compound is its reaction with Aryl diazonium tetrafluoroborates in ethyl acetate to give phosphonic acids. Trialkyl phosphites may also be used in a related reaction but are equally hard to get and their preparation requires PCl3.
Yamato71
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Freezing might work to separate CCl4 and PCl3. Their melting points are -23c and -94c respectively. Cooling to -78c with a dry ice/acetone bath should cause the CCl4 to crash out so that it can be filtered from the PCl3. I don't see why the PCl3 can't be used as a solution in CCl4 however as this would allow the reaction to be moderated.
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check out this site..
http://www.hottdealss.com/Red%20phosphorus.html

is that a set up or what?

woelen

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This is a ridiculous price, $30 for 20 grams. And then have a look at the top 2 chemicals, red P at number 1, iodine at number 2, also for a ridiculous price. This looks either like someone who wants to grab a lot of money from cooks or it is a setup. A normal price for red P is around EUR 10 per 100 gram or maybe$15 per 100 gram.

There are more signs of a not-so-professional thing. The red P is listed as P4, while having a molar mass of 31 grams. P4 is the formula of white P. This is someone who does not have any real chemical knowledge.

Conclusion: I would not buy a gram of any chemical from this place.

[Edited on 9-12-12 by woelen]

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neptunium
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thought so....there is a lenghty thread on making phosphorus with very interesting process...and results

[Edited on 9-12-2012 by neptunium]

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