danwillscott
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POCl3 from Phosgene and Phosphorus pentoxide
I am wondering if anyone has ever try this or know of it working. In MSDS for phosgene it states not to allow it to come in contact with phosphorus
oxides. Secondly can phosgene be easily converted from chloroform. I have made a few attempts at it using UV light(The light was weak so that could be
the problem) and introducing oxygen to it with very little luck. The amount of phosgene made was to low to actually use in any type of reaction.
I do understand the risks of phosgene before anyone starts to say how awful it is. With a full suit and an air supplied mask in a negative pressure
room the risks are minimal( I would not be stupid enough to say there is no risk since there always is one.) Also I have a very wide selection of lab
glassware and the like so the right apparatus won't be a problem to get my hands on.
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Dr.Bob
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I have never heard of making POCl3 from phosgene and P2O5, sounds like a mess at best. And while phosgene is likely a byproduct of decomp. of most
chlorinated solvents, most of those reactions give a mix of many things and are very hard to control. I don't think the industrial scale oxidation
of PCl3 would be practical in a lab, but the second step below looks reasonable, especially if you already have P2O5. For many reactions, PCl5 works
as well as POCl3 anyway, and it is usually a byproduct from them, so it provides several halogens per mole if making an acid chloride or iminoyl
chloride, for example. But POCl3 is one of the chemicals I would make every effort to buy if possible, much like thionyl chloride, which is easier
to make on an industrial scale, and not that expensive.
From http://en.wikipedia.org/wiki/Phosphoryl_chloride:
Phosphoryl chloride can be prepared by the reaction of phosphorus trichloride with oxygen at 20–50 °C (air is ineffective):
2 PCl3 + O2 → 2 O=PCl3
An alternative synthesis involves the reaction of phosphorus pentachloride (PCl5) and phosphorus pentoxide (P4O10). Since these compounds are both
solids, a convenient way of performing the reaction is to chlorinate a mixture of PCl3 and P4O10, which generates the PCl5 in situ. As the PCl3 is
consumed, the POCl3 becomes the reaction solvent.
6 PCl3 + 6 Cl2 → 6 PCl5
6 PCl5 + P4O10 → 10 POCl3
Phosphorus pentachloride also forms POCl3 by reaction with water, but this reaction is less easily controlled than the above reaction.
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ScienceSquirrel
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The easiest lab approach to phosgene is the reaction of carbon tetrachloride with oeum.
Neither of these reagents are readily available or cheap.
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danwillscott
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More details
In Phosgene: And Related Carbonyl Halides, Volume 24 page 371 it states P4O10+6COCl2=4POCl3 + 6CO2
I am sure the function of the reaction would work since I have found places that state the same thing. I am interested in Chloroform to Phosgene
simply because I have an abundance of Chloroform was attempting to find a way to convert the P2O5 I have into POCl3. Granted buying POCl3 is the
method of choice. The reaction of Chloroform to Phosgene doesn't have to be fast but slower then watching grass grow is also not the goal here either.
I have a fairly large amount of P2O5 from another experiment I did that I was able to get at a very low price. (about 2000 Grams left) I also have
some I made from drying Phosphoric acid. That is not something that is easily achieved without the right equipment.
So any idea's on Chloroform to Phosgene that might create a steady flow of Phosgene gas?
The first set up was 50ml of Chloroform in a 250ml 2 way ground glass round bottom flask. Through the top I ran a glass tube to the bottom of the
flask where I pumped Pure dry O2 at just under 1 PSI. the second had a down spout with a separation funnel that had a filter with 10G of P2O5. (the
theory was Phosgene would be forced down from the small amount of O2 past the thin layer of P2O5) After that a Long condenser was attached and 2
degree C water was pumped into it. at the bottom was a 2 way 500ml round bottom flask in an ice bath. The up another condenser was attached for safe
measure and the out water from the other condenser was attached. the out flow of air was pushed into 1500ml of distilled water and into a second flask
of water with a strong base to ensure no HCl would get out. All of this was in a negative pressure chamber. I should not the Chloroform was exposed to
UV light the whole time. The only thing I found was small amounts of chloroform moved through the whole system and the PH of the water went from 7.3
to 7.1 (that maybe be because of contamination so I can't use that as true evidence of phosgene interacting with the water. This ran for 5 hours
before I stopped it seeing nothing happening. I have never really experimented with the production of phosgene so I may in fact be doing something
wrong in this process. Any ideas?
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BromicAcid
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Tearing my hair out trying to figure out where I have the ref, but there is a preparation out there for making COCl2 from chloroform on the lab scale
using dichromate. Here is what I did find:
http://www.sciencemadness.org/talk/viewthread.php?tid=252
If I remember where the reference is I will post.
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Random
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myfanwy had a working procedure when I recall
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AndersHoveland
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Quote: Originally posted by danwillscott  | | Secondly can phosgene be easily converted from chloroform. I have made a few attempts at it using UV light(The light was weak so that could be the
problem) and introducing oxygen to it with very little luck. |
Yes, phosgene can be very slowly oxidized during storage. First the C-H bond is attacked. Cl3COH is not stable and immediately tautomerizes
to Cl2CO and HCl. I am not sure, but I think the C-H bond in chloroform, because it is more polar, is more readily oxidized than in typical
alkanes.
I think that chloroform can be spontaneously oxidized by air, without the need for light, but the rate of reaction is extremely slow, as I suspect it
has something to do with transient ionization of the hydrogen off the molecule.
| Quote: | Schoorl and Van den Berg confirmed the observation that in the absence of air or oxygen, chloroform is not affected by light exposure.
The decomposition of chloroform has been universally conceded to be an oxidation process. It is generally accepted that the chloroform is unaffected
by light alone, and that light, although it accelerates oxidation, is not a necessary factor in the process.
On exposure to air, in the absence of light, chloroform gave no precipitate with silver nitrate, even after four hours.
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I had another thought: would SCl2 react with P2O5 ?
P4O10 + 6 SCl2 → ? → 4 PCl3O + 3 SO2 + 3 S
Heat of formation for sulfur dioxide is −296.84 kJ/mol
Heat of formation for an equivalent of P4O10 is −3270 kJ/mol
Heat of formation of PCl3O is −636.5 kJ/mol
A quick calculation, however, suggests the reaction would not quite be favorable, at least not unless the SCl2 has an enthalpy above −28 kJ/mol
(I could not find an exact value anywhere), which is very unlikely.
I might be wrong, since I found conflicting entropy values for several of these compounds, so it might not be a complete waste of time if someone
wanted to confirm this through actual experiment. For example, using a slightly different reference entropy value for P4O10 would allow the SCl2 to
have an entropy as low as −63 kJ/mol. Actually, the difference on both sides of the equation was quite close, leaving some ambiguity.
In other words, my proposed reaction would probably not work, but the entropy calculations did not entirely rule the possibility out.
[Edited on 17-3-2013 by AndersHoveland]
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danwillscott
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Some very interesting thoughts. I could make my chloroform into carbon tetrachloride, and make oeum, but that would require buying stuff. (might end
up doing that in the end) I am going to attempt a mild heating of the chloroform in an oxygen environment with constant stirring in a closed container
to see if there is a reaction worth while. I wasn't really able to find anything on warm chloroform being more reactive but one can assume that it
would be. Hopefully I can try it today and see how it goes. Andershoverland I did read the same about oxygen reacting even without light with
chloroform. but it also says in some of the articles on it that it is a faster reaction with light involved. Guess I will find out soon.
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AndersHoveland
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I would suspect that the rate of reaction of iodoform with air would be much faster, for several reasons. Iodoform, however, does decompose
in the presence of light (even in the absence of oxygen), and furthermore there cannot be an moisture either since iodoform hydrolyzes much faster
than chloroform.
If you were curious, at neutral pH, chloroform has a half-life of 15 months in water. In comparison, the reaction rate for carbon tetrachloride is
neglibable under ordinary conditions, a half life of 7000 years has been calculated.
I am not sure that heating the chloroform will cause it to be oxidized any faster, at least not unless it is heated to combustion temperatures
(chloroform itself is actually not flammable in air).
My grandfather owned a small tank of dichlorofluoromethane refrigerant (it has since been banned). He sometimes used it for fumigation, passing the
gas over a torch flame. The refrigerant was converted to phosgene in the flame. My grandfather told us he simply held his breath so he would not
breathe any of it in. I would imagine the combustion equation is:
2 CHCl2F + O2 --> 2 COCl2 + 2 HF
[Edited on 17-3-2013 by AndersHoveland]
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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Rogeryermaw
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Industrially, phosgene is produced by passing purified carbon monoxide and chlorine gas through a bed of porous activated carbon, which serves as a
catalyst. ( http://en.wikipedia.org/wiki/Phosgene )
It can be accidentally produced by applying flame to R-12 refrigerant. Or, according to the article, it decomposes into HF and HCl and regenerates to
COCl2. ( http://www.ehow.com/about_6184357_dangers-freon-r12-gas-refr... )
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