Sciencemadness Discussion Board - Phosphorus suboxide?

Phosphorus suboxide?

woelen - 6-5-2013 at 23:27

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.

Finnnicus - 7-5-2013 at 00:38

Well, that is strange... What is the structure like I wonder..?
Can't help with your problem, sorry.

Simbani - 7-5-2013 at 00:57

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?

woelen - 7-5-2013 at 01:04

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.

Simbani - 7-5-2013 at 01:27

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

Adas - 7-5-2013 at 02:07

I think that the foul-smelling gas was PH₃. White phosphorus is known to dissolve in aqueous NaOH solution to form sodium hypophosphite - NaH₂PO₂.

woelen - 7-5-2013 at 02:39

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.

Adas - 7-5-2013 at 04:21

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.

blogfast25 - 7-5-2013 at 06:32

Quote: Originally posted by Adas

It seems very unlikely to me that something like "P4O" could exist.

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]

AJKOER - 7-5-2013 at 07:27

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.

Endimion17 - 7-5-2013 at 07:27

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 P4O exists, but I'm quite sure it would be extremely poisonous. Be careful, woelen.

[Edited on 7-5-2013 by Endimion17]

Nicodem - 7-5-2013 at 07:54

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)
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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]

blogfast25 - 7-5-2013 at 08:29

Quote: Originally posted by AJKOER

Congratulations on preparing Phosphorus tetritoxide.

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]

woelen - 7-5-2013 at 12:07

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]

ScienceSquirrel - 7-5-2013 at 12:31

I suspect that P4O may be possible under very special conditions.
Supposing you condensed P4 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 P4 moiety.
If you then allowed the solid to evaporate in to a spectrometer you might pick up these funnies.

AJKOER - 8-5-2013 at 18:15

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]

ScienceSquirrel - 10-5-2013 at 03:50

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 P4 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 P4O.
Argon matrix techniques;

http://en.wikipedia.org/wiki/Matrix_isolation

AJKOER - 10-5-2013 at 07:28

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).

woelen - 10-5-2013 at 08:21

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.

halogen - 10-5-2013 at 08:41

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?

Adas - 10-5-2013 at 12:23

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.