woelen
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Phosphorus suboxide?
I have an old German book of Vanino about preparative inorganic chemistry. It contains an interesting section on the compound with formula P4O, they
call it phosphorus suboxide.
Making this is done as follows:
- Take 2 volumes of ethanol
- Take 1 volume of a 10% solution of NaOH in water
- Mix the ethanol and NaOH-solution
- Take some white P and put this under hot water. Shake so that you get many small granules of white P (less than 1 mm diameter) and keep on shaking
until the water becomes cold again and the granules solidify.
- Decant the water from the granules of white P and quickly add the mix of ethanol and NaOH-solution.
According to the book I should get a blood-red solution of P4O in the ethanol/water/NaOH mix and production of gas. I indeed get production of a
colorless gas, which dissolves in the liquid for the most part before it reaches the surface. Around the white P I get some orange/brown color and on
shaking the liquid becomes yellow. I also notice an amazingly foul smell when I open the little bottle with the liquid. After 1 day, all of the white
P has dissolved and the liquid is pale yellow. After another day the liquid is colorless and clear and has a terrible foul smell.
I also tried this experiment with methanol instead of ethanol. The results are very similar.
According to the book, P4O can be precipitated from the blood-red solution by adding it to a dilute acidic aqueous solution (neutralisation of excess
NaOH), but in my case nothing happens, I get no precipitate. But I can understand that, because I have no blood-red solution. P4O is said to be a dull
orange/red powder, which can be ignited and burns in air with a lot of white smoke of P4O10. P4O is fairly inert and insoluble in water, but soluble
in ethanol in which it dissolves with an intense blood-red color.
I now doubt very much the existence of such a thing like P4O and it might be that this blood-red color, described in the book, is due to some
impurities in their phosphorus.
Any idea what this blood-red compound could be and why it only appears in very small quantity in my experiments? I like this obscure chemistry very
much, and would like to understand what really goes on. More experiments with and pictures of this "P4O" will follow.
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Finnnicus
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Well, that is strange... What is the structure like I wonder..?
Can't help with your problem, sorry.
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Simbani
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Angewandte Chemie International Edition
Volume 40, Issue 2, pages 378–381, January 19, 2001
DOI: 10.1002/1521-3773(20010119)40:2<378::AID-ANIE378>3.0.CO;2-7
Interesting, I will try it with red phosphorus in a moment. Did you use pure EtOH or the dirty stuff?
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woelen
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I tried with quite clean ethanol, but the ethanol is denatured (1% MEK). I distilled the ethanol once, knowing that any less volatile stuff remains
behind, but most of the MEK will be in the distilled ethanol as well.
For this reason I also tried with methanol, the latter is pure reagent grade.
The result is not very different with these two solvents.
I did this experiment with white P, not red P. I do not think that red P will react at all, it is quite inert in most situations and only very strong
oxidizers like bleach and solutions of halogens in suitable solvents react with red P.
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Simbani
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Yes I know it will probably not react, but I have no white P at the moment. Till now, no reaction is occuring. I´ll try heating it up to 50°C, but
it seems that it does not work.
I have to make a bit of WP tomorrow then 
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Adas
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I think that the foul-smelling gas was PH3. White phosphorus is known to dissolve in aqueous NaOH solution to form sodium hypophosphite -
NaH2PO2.
Rest In Pieces!
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woelen
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I know about the aqueous situation (I actually have a webpage on my site about formation of PH3 from white P and NaOH), but the presence of ethanol is
supposed to have a strong influence on the reaction and with that, P4O should be formed, according to the book of Vanino.
I do see some formation of a red/orange compound, but I think that the amount is very small and that indeed most of the white P ends up as PH3 and
NaH2PO2. What is strange though is that the gas does not inflame on contact with air. In my experiments with aqueous NaOH the gas inflames with puff
and white smoke rings when it comes in contact with air, in this experiment there is no such reaction. There actually is not any smoke at all.
The foul smell is not PH3. I have made PH3 quite a few times and I know its smell. The foul smell is much worse than the smell of PH3. I have the
impression that this smell is caused by a very small amount of some organic compound which has a really strong odor.
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Adas
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Then, it might be that it reacts with ethanol somehow. Would it be possible that it forms, say, ethyl phosphine? Have you also tried dissolving very
small amount of white P in some pure hot ethanol (or ethanolic NaOH solution)?
It seems very unlikely to me that something like "P4O" could exist.
Rest In Pieces!
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blogfast25
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Only if you believe simple (and effective) rules like the 'octet rule' always apply. There are many compounds that defy the simple selection rules.
Molecules are complicated quantum systems that often don't appear to comply with our perceived rules of how atoms combine. The simplest example is
probably the 'electron deficient' diborane (B2H6) but there are plenty others.
[Edited on 7-5-2013 by blogfast25]
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AJKOER
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From one of my favorite sources again on P4O:
"A solid substance said to be tetraphosphorus monoxide, or phosphorus tetritoxide, P4O, has been prepared by a number of reactions, amongst which may
be mentioned the slow oxidation of phosphorus in ether, and the reduction of phosphorus pentoxide with ammonia, followed by treatment to remove other
oxides, namely, washing and evacuation. The removal of water from hypophosphorous acid is said also to yield this product, thus
4H3PO2 = P4O + O + 6H2O
Acetic anhydride in the presence of glacial acetic acid has been used as the dehydrating agent. A solution of phosphorus in 10 per cent, aqueous
caustic soda with twice its volume of alcohol yielded on acidification a greenish-yellow solid to which the same composition was assigned. The
substance prepared by various methods has a red or orange colour and a density of about 1.9. It is a mixture, the composition of which may be inferred
from the facts that it retains hydrogen and moisture, that it gives phosphorus and phosphorus pentoxide when heated in an indifferent gas, and that
when distilled in chlorine it yields phosphorus oxychloride as well as the pentachloride.
The supposed compound P2O is also a mixture of finely divided phosphorus with phosphorous acid."
Source: http://phosphorus.atomistry.com/phosphorus_suboxides.html
Note Woelen observation: "Around the white P I get some orange/brown color and on shaking the liquid becomes yellow" as compared to the above
description "The substance prepared by various methods has a red or orange colour and a density of about 1.9".
Congratulations on preparing Phosphorus tetritoxide.
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Endimion17
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I'm always extra cautious when reading very old textbooks. The more you look back in the past, the more often people published whatever they felt was
true, or simply copied unverified work from even older books.
I don't know if P<sub>4</sub>O exists, but I'm quite sure it would be extremely poisonous. Be careful, woelen.
[Edited on 7-5-2013 by Endimion17]
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Nicodem
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Quote: Originally posted by Simbani  | Angewandte Chemie International Edition
Volume 40, Issue 2, pages 378–381, January 19, 2001
DOI: 10.1002/1521-3773(20010119)40:2<378::AID-ANIE378>3.0.CO;2-7 |
| Quote: | | While the molecular phosphorus subsulfides P4S3, P4S4, and P4S5 are well known,[1]
various attempts to prepare the corresponding molecular phosphorus suboxides have failed so far. In its polymeric form phosphorus suboxide
"P4O" was already mentioned in 1832[2] but in molecular form P4O has been detected only in rare gas matrices.[3] Using IR
spectroscopy combined with ab initio calculations[4] it was possible to identify the geometries of three different isomers of P4O. The energetically
most favorable isomer of P4O possesses a planar five-membered ring (isomer I in Table 1), while a terminal (isomer III in Table 1) and a
bridged-bonded isomer (isomer II in Table 1), which are closely related to the tetrahedral structure of the P4 molecule, were found to lie
much higher in energy.[4] |
Attachment: About the Chemistry of Phosphorus Suboxides.pdf (204kB)
This file has been downloaded 1233 times
Edit: Gallica unfortunately misses the 1832 volume of Annales de chimie et de physique, so unless another source is found, the only way to get the article is
visiting a scientific library and order an interlibrary loan. That, or just trust that Vanino correctly translated the procedure.
[Edited on 7/5/2013 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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blogfast25
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It takes a bit more than the 'if it looks like a duck' approach. At a minimum some characterisation of woelen's substance would be needed to
substantiate the claim.
I second Endi's assertion: too many uncorroborated claims in some of these very old sources.
[Edited on 7-5-2013 by blogfast25]
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woelen
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Nicodem, thanks for posting that article. It is very enlightening.
I already had doubts about the existence of P4O and I now am more inclined to think that the deep red compound, mentioned by Vanino is another
compound. The article, posted by Nicodem, shows that P4On becomes more and more energetically favorable for increasing n. So, P4O is the least
probable oxide.
Known and verified oxides, mentioned in newer books (e.g. Chemistry of the elements by Earnshaw and Greenwoord) have formulas P4On, with 6 <= n
<= 10. The most common ones are P4O6 and P4O10. P4O6 has the top right structure, described in the article, posted by Nicodem and the higher oxides
have the same structure with additional O-atoms attached to (some of) the P-atoms, pointing outwards.
But given this information, I even more wonder what the dark red compound, mentioned by Vanino is. It might be a mixture, but still it is remarkable
material. I first try to reproduce Vanino's results. Till now I only have faint indications of the existence of this red compound, but the effect is
too weak to be really convincing. It is far from blood-red, it only is pale orange. This means that either very small amounts are produced, or Vanino
(or his source of information) used impure chemicals, which is not uncommon around 1900.
[Edited on 7-5-13 by woelen]
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ScienceSquirrel
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I suspect that P<sub>4</sub>O may be possible under very special conditions.
Supposing you condensed P<sub>4</sub> in to a low temperature matrix of carbon dioxide and then added a trace of oxygen. It is possible
that you could create molecules with one or two atoms of oxygen per P<sub>4</sub> moiety.
If you then allowed the solid to evaporate in to a spectrometer you might pick up these funnies.
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AJKOER
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A more recent work citing P4O and other oxides (see "An ab initio characterization of the tetraphosphorus oxide P4O" by
Lawrence L. Lohr in J. Phys. Chem., 1990, 94 (12), pp 4832–4835. Link: http://pubs.acs.org/doi/abs/10.1021/j100375a015
-------------------------------------------------
OK, here is my personal argument for verifying that P4O was, indeed, formed. The compound on heating in an inert gas should decomposes into P and
P2O5. Assume the products and quantities observed is 18 parts of P to one part of P2O5, or:
5 P4O --> 18 P + P2O5
then, at least on average, one could argue that the formula is correctly P4O.
Similarly, the observed products when "distilled in chlorine" being phosphorus oxychloride and the pentachloride could suggest an average chemical
formula as well.
In my opinion, the compounds apparent distinctive color and lower solubility relative to other phosphorous oxides, makes the argument that the
compound does not exist or was not formed, and is instead a combination of say P2O and other higher phosphorous oxides less likely (in my opinion, it
is a matter of math and observed solubility differences between the phosphorous oxides).
[Edited on 9-5-2013 by AJKOER]
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ScienceSquirrel
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| Quote: Originally posted by AJKOER | A more recent work citing P4O and other oxides (see "An ab initio characterization of the tetraphosphorus oxide P4O" by
Lawrence L. Lohr in J. Phys. Chem., 1990, 94 (12), pp 4832–4835. Link: http://pubs.acs.org/doi/abs/10.1021/j100375a015
-------------------------------------------------
OK, here is my personal argument for verifying that P4O was, indeed, formed. The compound on heating in an inert gas should decomposes into P and
P2O5. Assume the products and quantities observed is 18 parts of P to one part of P2O5, or:
5 P4O --> 18 P + P2O5
then, at least on average, one could argue that the formula is correctly P4O.
Similarly, the observed products when "distilled in chlorine" being phosphorus oxychloride and the pentachloride could suggest an average chemical
formula as well.
In my opinion, the compounds apparent distinctive color and lower solubility relative to other phosphorous oxides, makes the argument that the
compound does not exist or was not formed, and is instead a combination of say P2O and other higher phosphorous oxides less likely (in my opinion, it
is a matter of math and observed solubility differences between the phosphorous oxides).
[Edited on 9-5-2013 by AJKOER] |
Your reference states that it was made using an argon matrix.
This means molecules of P<sub>4</sub> were deposited on a window covered with solid argon after which oxygen atoms were added.
I doubt that there was more than a few milligrams of reactants and maybe a few thousand molecules of P<sub>4</sub>O.
Argon matrix techniques;
http://en.wikipedia.org/wiki/Matrix_isolation
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AJKOER
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Actually ScienceSquirel, the reference says that P4O (along with PO and PO2) were formed by the direct reaction of O and Phosphorous.
Then, using an argon matrix, which per your Wiki reference allows the sample to be studied using various spectroscopic procedures, and to do so more
easily. Here is a quote from Wikipedia:
"Mono-atomic gases [like Argon] have relatively simple face-centered cubic (fcc) crystal structure, which can make interpretations of the site
occupancy [in the Argon matrix] and crystal-field splitting of the guest easier."
My take on all this is that even a direct reaction between phosphorous and oxygen (and not any of the reputed paths to the formation of P4O)
apparently forms in small amounts, these rare oxides. My only firm conclusion is that P4O does exists, with no further insight as to whether the
reputed paths to P4O actually produce solely P4O (or is it, for example, some adduct of phosphorous with one or more phosphorous oxides).
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woelen
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I repeated the experiment with pure ethanol now (not denatured, 96% ethanol, the rest being water) and now I indeed get a blood-red liquid around the
granules of phosphorus. When the liquid is shaken, then it becomes orange, but on standing the color fades again. There also is not such a foul smell.
So, the presence of MEK has a notable influence, it makes formation of the red compound more difficult or causes faster decomposition of the red
compound. Apparently MEK reacts and forms a foul-smelling compound.
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halogen
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Now that's interesting itself, wonder what the odoriferous material is and whether it can be isolated. My guess is obvious if misguided. Phosphine
ligand for woelen's metal complexes?
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Adas
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| Quote: Originally posted by woelen | I repeated the experiment with pure ethanol now (not denatured, 96% ethanol, the rest being water) and now I indeed get a blood-red liquid around the
granules of phosphorus. When the liquid is shaken, then it becomes orange, but on standing the color fades again. There also is not such a foul smell.
So, the presence of MEK has a notable influence, it makes formation of the red compound more difficult or causes faster decomposition of the red
compound. Apparently MEK reacts and forms a foul-smelling compound. |
That is very interesting, so the foul-smelling compound could possibly be CH3-CH2-C(OH)(PH2)-CH3. I assume this because phosphine reacts similarly to
ammonia in some cases. It would be nice if somebody could define the compound. Its concentration could be increased by adding normal MEK.
Rest In Pieces!
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