Sciencemadness Discussion Board - really weird compound

really weird compound

woelen - 5-12-2008 at 14:17

I now finally have some PCl5 (just a small quantity, but enough for a few really cool experiments).

I did a simple experiment in which I mixed approximately 2 parts of PCl5 with 1 part of V2O5. The yellow/ochre V2O5 at first does not seem to react with the PCl5 but on slight heating the mix first darkens and then suddenly puffs up, giving a plume of brown fumes (small brown droplets) and brown droplets collect at the glass which run downwards again.

After a while, there is a partly solid, partly liquid mix at the bottom and brown droplets on the glass walls. I heated this mix again and if this is done, then all of the material evaporates, giving a green gas (slightly blue), which condenses on colder parts of the glass as a very dark brown liquid. The color of the gas is really peculiar, I have never seen something like that before. The gas is not green like chlorine, but much brighter green with a hint of blue.

The contrasts are very strong. The color of the gas is not that strong (stronger than the color of Cl2, but much paler than the color of NO2), while the droplets of liquid have an intense brown color. On strong heating of the test tube, this results in a green/cyan gas and a brown ring of liquid, which is moving upwards in the test tube while the tube is heated.

What could this compound be? Is it VOCl3? I have a book, which describes VOCl3 as brown liquid, but it does not mention the strange green/cyan gas. If someone has a good description of this compound, then that would be nice.

I'll make a webpage about this experiment next weekend, so expect some nice pics and videos within a few days. This is something, which I really want to share with others.

After the experiment, I added a few ml of water and this results in another beautiful effect. The liquid becomes lime green/yellow (mix of traces of blue vanadyl ions with pale yellow pervanadyl ion) and above the liquid there is a heavy yellow smoke and in the liquid there is a yellow precipitate. The yellow smoke and precipitate most likely are V2O5.

If someone wants to repeat this experiment, please use small quantities and assure that no fumes and/or smoke are inhaled. Vanadium salts are quite toxic and inhaling the gas does not seem like a good thing. Besides that, PCl5 is very corrosive, it reacts with water to HCl and H3PO4, which both are corrosive.

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I also did another experiment with PCl5 which is worth mentioning. When this is added to solid CrCl3.6H2O and slightly heated, then a strange reaction occurs, in which two layers of liquid are formed. A lower almost dark liquid and an upper colorless liquid. Bubbles of gas (HCl) are produced as well. When a large excess of PCl5 is used, then a pink solid is formed and the dark liquid disappears. This pink solid must be anhydrous CrCl3 (which according to my books is rose/pink). Making anhydrous CrCl3 is very difficult and it is an elusive compound, but with PCl5 it is possible.

Jor - 5-12-2008 at 14:41

Im really impressed you made a green/blue gas. I have never seen this before, and i'm really looking forward to see this.

It might be VOCl3, as well as V2O3Cl4, a product of hydrolysis. Literature decribes the VOCl3 as lemon-yellow liquid...

I want to try this myself! A green gas, amazing! I need PCl5 thoughm wich cannot be bought (CWC). So I have to do the route via red P in CHCl3. Something keeps me from doing it though. Doesn't sound like the easiest synthesis.

I have heard that the easiest way to prepare CrCl3 is heating the hydrate with tetra... My professor told me. Phosgene is evolved but small amounts aren't too bad outside or in a hood.
Thionyl chloride might be a better option, I think it will work. SO2 and HCl nicely bubble away.

Sorry I havent yet answered your emails woelen, Im busy at the moment. I think i will do this weekend.

Formatik - 5-12-2008 at 15:30

The vapors of VOCl3 are said to be green-yellow in Gmelin, but they give the description for the liquid as a clear, easily mobile, bright yellow liquid. This reminds me of N2O3. N2O3 as a liquid has a nice bright indigo color, but evaporates to brown fumes.

[Edited on 5-12-2008 by Formatik]

woelen - 6-12-2008 at 05:46

My observations are somewhat mixed. At low concentration, the gas appears green with a cyan hue. At higher concentration (which can only be achieved by stronger heating), the color shifts towards yellow and then the color is green with a yellowish hue and under such conditions the color of the gas is quite intense. So, apparently the color also is somewhat depending on temperature.

When the green gas is poured out in cold air, it immediately condenses giving a red/brown smoke. All of this is on video now and a webpage about this will follow soon

Formatik - 6-12-2008 at 14:03

Color changes, especially exotic ones make some pretty interesting chemistry. Gmelin also says in moist air the yellow-red fog of VOCl3 consists of V2O5. Mixing it with a little water the VOCl3 also becomes thick and blood-red due to formed V2O5 hydrate, and upon heating becomes nicely blue. With more water it forms a clear, pale-yellow solution which on standing several days or upon heating forms Cl2 and vanadium tetrachloride first turning green, then blue according to Berzelius. But according to Safarik the pale-yellow solution when evaporated off, leaves behind red V2O5 hydrate without turning blue.

woelen - 7-12-2008 at 05:55

I made videos and a webpage about this experiment:

http://woelen.homescience.net/science/chem/exps/v2o5_pcl5/in...

It is a beautiful experiment, but the results are somewhat variable. The color of the gasmix is not entirely constant, it seems to depend on temperature and on the ratio of PCl5 and V2O5 used. Using more PCl5 seems to result in a somewhat more yellow gas mix (more chlorine?). In the experiment on the webpage I used 4 times as much PCl5 as V2O5. When much V2O5 is used, then a lot of black crud remains, which does not volatilize on heating.

I also do not have a real good idea of what products are formed. Maybe some of you can give interesting suggestions, such that the theoretical background of the webpage can be improved?

This experiment certainly forms a basis for more interesting experimenting.

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I also did a similar experiment with V2O5 and SOCl2. This experiment does not give any interesting result. The yellow/ochre V2O5 remains suspended in the SOCl2. Even when it is refluxed for some time at the boiling point of SOCl2 nothing seems to change. On addition of water, the SOCl2 dissolves and a lime green turbid liquid is obtained (containing blue vanadyl and suspended yellow V2O5).

[Edited on 7-12-08 by woelen]

blogfast25 - 7-12-2008 at 08:36

Very interesting webpage and experiment.

What made you think of mixing PCl5 and V2O5? An attempt at chlorinating Vanadium?

This is just a guess but the colour changes might be due to a species toggling between a monomeric and a dimeric state. Several mostly non-heteropolar higher metal chlorides are known to do that. Even AlCl3 does it (but w/o colour change).

I wonder if VCl4 could be prepared by direct chlorination of the pentoxide...

Swany - 7-12-2008 at 13:36

Very interesting woelen! I was waiting for the excellent pictures that I knew would come. Perhaps you should attempt to prepare a high oxidation number vanadium chloride and add P2O5? Other than that, if it was possible to control the stoicheometry on such a small scale, you could perhaps more easily predict what would be formed, as it obviously does depend on amounts of what is present.

Jor - 7-12-2008 at 13:59

Very nice woelen!
I'm very impressed. That's a beautiful green color.
Do you think it is possible, that PCl5 and V2O5 form a compound together?

In the safety warnings, you wrote phosphorus pentoxide, instead of pentachloride

Fleaker - 7-12-2008 at 14:30

Nice page as usual Woelen! I cannot wait to try this experiment. I too noticed that you carried down the pentoxide from vanadium down to the phosphorus

Jor - 7-12-2008 at 15:02

Fleaker, do you also have access to PCl5? If yes, where do you live? I can buy most things, but PCl5, just as other phosphorus chlorides is not possible, in any amount, unless I want the police here (CWC3). Woelen lives in the same country as me, and he cant buy it from the regular suppliers as well, but I know where he got his lucky 25g

But I have not yet heard of any other member having this hoy grail. Yes garage chemist made it, but AFAIK noone has bought it.

Fleaker - 7-12-2008 at 15:25

Yes, I do have access to it and I live in the United States. I am in the United States. Also, 25g is an awfully small quantity, I would think perhaps 1kg would be restricted, but I also know nothing of EU laws or CWC statutes.

woelen - 8-12-2008 at 11:51

@blogfast25: There is not a particular reason why I did this experiment. I like to try unusual combinations of chemicals and sometimes that leads to really interesting and fascinating compounds.

@Fleaker: If you have PCl5 then you certainly should try the experiment yourself. Seeing the reaction occur yourself cannot be matched by whatever video or picture. Especially the start of the reaction, when the orange/red cloud rises up in the test tube really looks impressive and weird.

@Swany: I wish I could do this experiment on a larger scale, but my supply of chemicals is very limited, so I'll have to stick to qualitative experimens. What I can do is repeat the experiment with a large excess of V2O5 and see what it the result in that case.

@Jor: I'll change the webpage and remove the error. Thanks for telling me about this.
I do have a suggestion for you:
- suspend some red P in 2 ml of CH2Cl2
- carefully and slowly bubble Cl2 through the liquid, until all red P is gone and then continue bubbling, until the liquid looks green
- to this liquid add some V2O5 and boil off the CH2Cl2
- continue heating. I'm quite sure that you will then see a similar reaction as I have. It's a little more hassle, but you can do it, on a test tube scale. No need to isolate the PCl5.

woelen - 18-12-2008 at 14:29

I did the same experiment with PCl5 and MoO3. Surprisingly the effect is very similar to what I show in the video on the webpage. A red/brown smoke is formed and a colored gas. The gas is orange/brown in this case, a little bit like bromine vapor, but with a much less intense color.

When 30% hydrochloric acid is added to the cooled down stuff, then a clear blue liquid is obtained, which on addition of much water becomes almost black and turbid.

I did a similar experiment with a mix of PCl5/Zn/MoO3 and with this mix, there is much more of the red/brown vapor.

This is a line of expeirmenting which is quite interesting. A lot of things can be varied and I am planning to do more investigations in this direction. A nice variation is to use WO3 with and without zinc-powder. This gives yellow/green vapor and red vapor and solid material in a plethora of colors (black, blue, brown/red. purple, bright yellow).

All of the metals vanadium, chromium, molybdenum, wolfram and niobium form volatile (oxy)chlorides and the metals molybdenum and wolfram even seem to form multiple volatile (oxy)chlorides, all of them having strong colors, also in the vapor-phase. I hope I can show some of these vapors in a reasonably pure state. I have a book of Vanino (old German book), which describes vapors like deep blue, bright red and all kinds of red to yellow shades. I only have seen the yellowish and red shades up to now.

[Edited on 18-12-08 by woelen]

Bedlasky - 11-3-2020 at 06:40

I tried prepare these metal oxychlorides with concentrated sulfuric acid and sodium chloride, but without success. I tried it with KMnO4, K2Cr2O7, V2O5 and Na2MoO4. Only reaction with dichromate worked. Conc. sulfuric acid isn't that powerful dehydrating agent to form these oxychlorides. Maybe oleum works?

With V2O5 I was little scared for a few seconds. I saw lot of white vapor going from the test tube. I thought: Shit! I breath some volatile vanadium compound! But after that I just realized, that white vapor was probably only HCl gas

woelen - 11-3-2020 at 11:52

No need to worry about volatile vanadium compounds. These compounds are strongly colored and if your fumes were white, it must have been HCl from the acid and NaCl.

A combination of oleum and HCl in some cases gives interesting results, but only in some cases. With V2O5 there is no interesting reaction. With KMnO4 there is a strong reaction, formation of green MnO3Cl, which quickly decomposes to MnO2, Cl2 and O2.
Beware with oleum. It is insanely corrosive and the reaction with HCl is intensely exothermic. You really need to moderate the reaction (e.g. slowly add HCl to oleum, while constantly mixing the liquid and having pauses in between to allow cooling down). The reaction between oleum and HCl gives chlorosulfonic acid. If you can buy chlorosulfonic acid, then you can do quite a few ineresting experiments, but it certainly is not a replacement of the very interesting PCl5. I can buy chlorosulfonic acid, but I cannot buy PCl5.

Bedlasky - 20-3-2020 at 20:36

Quote: Originally posted by woelen

I did the same experiment with PCl5 and MoO3. Surprisingly the effect is very similar to what I show in the video on the webpage. A red/brown smoke is formed and a colored gas. The gas is orange/brown in this case, a little bit like bromine vapor, but with a much less intense color.

When 30% hydrochloric acid is added to the cooled down stuff, then a clear blue liquid is obtained, which on addition of much water becomes almost black and turbid.

I did a similar experiment with a mix of PCl5/Zn/MoO3 and with this mix, there is much more of the red/brown vapor.

This is a line of expeirmenting which is quite interesting. A lot of things can be varied and I am planning to do more investigations in this direction. A nice variation is to use WO3 with and without zinc-powder. This gives yellow/green vapor and red vapor and solid material in a plethora of colors (black, blue, brown/red. purple, bright yellow).

All of the metals vanadium, chromium, molybdenum, wolfram and niobium form volatile (oxy)chlorides and the metals molybdenum and wolfram even seem to form multiple volatile (oxy)chlorides, all of them having strong colors, also in the vapor-phase. I hope I can show some of these vapors in a reasonably pure state. I have a book of Vanino (old German book), which describes vapors like deep blue, bright red and all kinds of red to yellow shades. I only have seen the yellowish and red shades up to now.

[Edited on 18-12-08 by woelen]

I read something about these compounds on atomistry and wiki:

http://tungsten.atomistry.com/tungsten_oxychlorides.html

http://molybdenum.atomistry.com/molybdenum_oxychlorides.html

http://molybdenum.atomistry.com/molybdenum_pentachloride.htm...

https://en.wikipedia.org/wiki/Molybdenum_oxytetrachloride

Bedlasky - 1-4-2021 at 23:39

Quote: Originally posted by woelen

I came across interesting paper today.

https://sci-hub.se/https://pubs.acs.org/doi/pdf/10.1021/ja02...

There is stated, that WO3 react with PCl5 to form WCl6, while MoO3 form MoCl5.PCl5.