Sciencemadness Discussion Board - (HPO3)n Dehydrating agent (polyphosphoric or metaphosphoric acid)

(HPO3)n Dehydrating agent (polyphosphoric or metaphosphoric acid)

simply RED - 3-9-2005 at 15:43

From "Inogranic chemistry - by Dobri Lazarov"
----------
Diphosphoric acid is synthesized by heating the orto-acid to 215 degrees C.
2H3PO4 = H4P2O7 + H2O

If you heat H3PO4 to 316 degrees C, metaphosphoric acid is synthesized. It exists in cyclic and polymeric forms and has the brute formula HPO3.
--------------
HPO3 is very strong dehydrating agent that could be used instead of acetic anhydride in RDX, HMX, TNT and other synthesis.
It could be possible to prepare HPO3n from normal 85% H3PO4 (1,5 dolars per liter) by heating (could it be concentrated to 100% by heating?).
Then 100% H3PO4 (melting point 42,3 degrees C) will be heated slowly to 316 C (electric stove will work).
Anyway it is unclear how long it must be heated to the upper temperature. To get 95% + yield ot HPO3n.

E.b.C: Title

[Edited on 4-9-2005 by chemoleo]

simply RED - 3-9-2005 at 16:07

Additional info from another source:
phosphoric acid

The most common, orthophosphoric acid, H3PO4, is usually simply called phosphoric acid. Two molecules of it are formed by adding three molecules of water, H2O, to one molecule of phosphorus pentoxide (phosphoric anhydride, P2O5). It occurs as rhombic crystals or as a viscous liquid; both are deliquescent. The crystals melt at about 42°C. It has specific gravity 1.834 at 18°C, is soluble in alcohol, and is very soluble in water. It is a tribasic acid and forms orthophosphate salts with either one, two, or all three of the hydrogens replaced by some other positive ion. When it is heated to about 225°C, it dehydrates to form pyrophosphoric acid, H4P2O7; at still higher temperatures metaphosphoric acid, HPO3, is formed.

BromicAcid - 3-9-2005 at 16:10

From Hawley's Condensed Chemical Dictionary:

Quote:

Pyrophosphoric acid
Derivation: By heating phosphoric acid at 250-260C. Further heating produces metaphosphoric acid.

Phosphoric acid, meta- (HPO3

x
Derivation: By heating ortophosphoric acid to redness, by treating phosphorus pentoxide with a calculated amount of water, by heating diammonium phosphate.
Use: Phosphorylating agent, dehydrating agent, dental cements, labratory reagent.

Sounds easy, phosphoric acid is non-volitile, just crank up the heat. What are you going to do it in, clay?

Edit: Posted simultaneously with simply RED

[Edited on 9/4/2005 by BromicAcid]

chloric1 - 3-9-2005 at 16:28

here is the real problem. No silicates! Hot 85% H3PO4 dissolves porcelin, (Cannot spell). This would also include most clays, glass, and even alumina because this forms aluminum phosphate. If platinum curcibles are out of question,maybe hastleoy or Inconel might work. I here 914 stainless is supposed to be phosphoric acid resisitant but not absolutely positive on this.

neutrino - 3-9-2005 at 17:40

While it is true that hot phosphoric acid will eat glass, this is a very slow process. Boiling your acid in a glass beaker shouldn't be too problematic.

Polverone - 3-9-2005 at 17:44

If phosphoric acid dissolves glass, it does so only to a minor extent. I have heated phosphoric acid to red heat in test tubes and not noticed any effects beyond the normal test tube damage that comes with thermal abuse. I have also heated phosphoric acid to the point that it formed a solid and the pyrex was melting around it.

I have heated diammonium phosphate in ordinary soda glass until it melted and then considerably thickened. I was able to draw it out in long strongs that went brittle like glass as it cooled. The glass vessel cracked on cooling, but there was no other damage visible. The solid material was quite hygroscopic, rapidly growing sticky on its surface.

In any case, I think you will have little trouble heating phosphoric acid to 316 C in glass, but I would suggest using something expendable as you may crack the glass on cooling.

Nicodem - 4-9-2005 at 00:32

Making pyrophosphoric acid (H4P2O7) from H3PO4 is no problem. Once I was about to follow the procedure in Organikum which states that you have to heat 85% H3PO4 at 150°C under vacuum for 6h, but since it seamed to me that this takes too much time I heated to 200-250°C untill the weight of the liquid fell at the theoretic amount for the H4P2O7 composition (about 2-3h). No glass etching was noted and the resulting poliphosphoric acid is a very viscious liquid (it gets a bit dark, perhaps from impurities in H3PO4).
However I doubt that heating it more would result in the formation of 'HPO3' in a fast process. It may take many hours at >300°C in vacuum. Not really practical I guess.

simply RED - 4-9-2005 at 13:23

Pyrophosphoric acid is also not bad as RDX synth. media.
HPO3 mixed with CH3COOH has been used to extract vitamine C in some analytical cases.
Do you know the physical properties of HPO3 and H3PO4, P2O5, HPO3, H4P2O7 solubility in diethyl ether?

garage chemist - 4-9-2005 at 13:39

(HPO3)n is a real kickass dehydrating agent, stronger than oleum for example. It dehydrates H2SO4 to SO3, look at the procedure I posted in the "oleum and SO3" thread.

Now, let's talk about its preparation.

Its ability to attack glass in the hot stage is a problem.
As I found out today, it attacks also iron very badly, a lot of hydrogen is evolved and the crucible started to dissolve!
Then I used a quartz crucible, and incredibly, it was also attacked!

However, the attack was much less severe than with glass. My beaker in which I did the first preparation got attacked considerably, and the walls are now noticeably thinner.
On the contrary, the walls of my quartz crucible now feel as if they were a bit THICKER. Maybe the quartz forms some sort of protective layer after some time which prevents further attack.
For the next batches of (HPO3)n, I'll use my quartz crucible.

I have yet to try my nickel crucible. This will also be one of the next experiments.

Does anyone know what kind of reaction is responsible for the attacking of quartz?

If someone finds out which metal is resistant to hot 85% H3PO4 and also to (HPO3)n at red heat, please post it here.

BromicAcid - 4-9-2005 at 13:56

Couldn't copper be used, it is only attacked by sulfuric at high temperatures due to the oxidizing power of that acid at those temperatures, however phosphoric being even less oxidizing should work for this. Copper endcaps for pipe work are highly avalible, I will try to boil down phosphoric acid in copper on Tuesday unless someone else gives it a shot first.

polyphosphoric acid

catfish - 4-9-2005 at 18:18

hey all, just wondering where this could be obtained, since it's not on the lists in the reagent/ acquisition forum.
Or made.
Thx in advance.

BromicAcid - 4-9-2005 at 18:49

When looking for a chemical avalible OTC that is not on a list, you can try the Household Products Database in which you can enter a chemical name and get a list of products that contain it, polyphosphoric acid only appearing in one of the listings.

Is polyphosphoric acid not just metaphosphoric acid? Metaphosphoric acid having the formula (HPO3

x due to it being a polymer type substance of HPO3 units (Is there a sharp distinction between the two?). I noticed you already posted a similar question in the thread dedicated to the manufacture of that substance, and as such I really don't see why you started this thread.

Upon looking up polyphosphoric acid in my chemistry dictionary I find that it is just a mixture of acids, e.g., dehydrated phosphoric acid containing phosphoric, pyrophosphoric, and metaphosphoric acids in different concentrations, so kind of like a commerical mixture that is sold for various purposes, polyphosphoric is denoted as having a H3PO4 precentage of 115% technically. So you can just heat phosphoric acid to make it. I don't know where this would be OTC, but phosphoric is avalible enough in most places.

catfish - 4-9-2005 at 18:53

Bromic, thx for answering...the reason I started another thread was because the old one was deleted somehow.
I can get phosphoric acid no problem...could you point me in the direction of some more concrete temps...?
Thx again.

Nicodem - 5-9-2005 at 00:28

There already is a thread discussing the production of polyphosphoric acid:
https://sciencemadness.org/talk/viewthread.php?tid=4409

And if you would have read it you would see that there already are described the needed conditions for making polyphosphoric acids of various concentrations. In my post there, for example, I described how to make the pyrophosphoric acid in a very simple way(polyphosphoric with the 78% concentration if expresed as P2O5 - a concentration convention often used in literature). The comercial PP is usually of a bit higher concentration (usually 83% P2O5 or more).

garage chemist - 5-9-2005 at 13:13

A new idea.

Can (HPO3)n dehydrate amides to nitriles?

If yes, we could make our own acetonitril from acetamide (which in turn can be made from ethyl acetate and ammonia, see frogfots page).

Or if we have a good fume hood, we could dehydrate formamide (easily produced from ethyl formate and ammonia) to hydrogen cyanide and use that to make extra-pure NaCN and KCN.

ADP - 5-9-2005 at 16:46

About the preparation of pyrophosphoric acid:
If one obtains 85% H3PO4 and dehydrates by boiling, what temperature is favorable for this? I know that H3PO4 has a BP of 158*C, Would I then not want to heat to the boiling point? Wouldn't the H3PO4 start boiling away faster than it would become pyrophosphoric acid? I know that the first post states 210*C. Also how long must this temp be held to know when a full conversion has been obtained? When it stops fuming H2O?

12AX7 - 5-9-2005 at 16:56

Apparently the boiling only refers to the water content (like how hydrated salts melt at a temperature then dry out).

Seems pretty Easy to me, just heat the junk up to red heat for an hour or so, maybe in a cordierite boat since it's more refractory and lower in shrinkage than cheap glass.

Tim

ADP - 5-9-2005 at 19:23

True, after reading some, in this case yes it is nessecary to heat to 215dC but at some point, H3PO4 will evaporate after boiling, but just not as fast as it will dehydrate at this temperature.

ADP - 6-9-2005 at 13:59

In my Chemistry textbook entitled: Chemistry by Steven S. Zumdahl, It states:

Quote:

Phosphoric acid easily undergoes condensation reactions, where a molecule of water is eliminated in the joining of two molecules of acid.

It then goes on to show two molecular diagrams of H3PO4 --> H4P2O7. Then it states "The product is called pyrophosphoric acid. Further heating produces polymers, such as tripolyphosphoric acid." And it gives the nomenclature H5P3O10. Where does metaphosphoric acid come from in all of this? And how does this stucture form?

BromicAcid - 6-9-2005 at 16:07

Today I heated ammonium phosphate at high temperatures (But how to convert ammonium phosphate to diammonium phosphate? Oxalic acid?) Anyway, it heated nicely giving off lots of ammonia and turning some very pretty colors, I noticed that in the hottest areas of the vessel it turned white, upon cooling the vessel cracked, included is a picture of it, very pretty.

Also, I tried to make phosphoric acid via the wet method today, 185 ml of conc (~16 M) H2SO4 was dilluted with 30 ml of distilled water and with stirring to 310 grams of bone ash Ca3(PO4

2 was added. So one mole of calcium phosphate to 3 mol sulfuric acid, stoichiometric quantites. At first things mixed well but there was quite a bit of heat generated, and after half of the bone ash was added I had a paste, after all of it was added I had solid (that gave off fumes that smelled like HCl). I added 100 ml of water and later another 50 ml of water and in the end I had a thin water layer.

I allowed to settle overnight and the next day I filtered the whole mess in sections, giving me nearly 300 ml of liquid. The liquid was boiled down to 40 ml of black foul smelling liquid, with obvious sulfuric acid content (it gave off white fumes cause I heated it too high).

Overall I consider the wet process a failure, I will try it with more dillute sulfuric in the future. Anyway, I tried to make some metaphosphoric acid today, but failed, failed to get the inital phosphoric and broke my beaker for my other attempt, better luck next week right

BTW, ADP, I have a similar entry in my book Descriptive Inorganic Chemistry third edition. It is obvious to see how the structure of metaphosphoric acid forms just from the way you explain things.

3(HO)3PO ---> (HO)2PO-P(OH)O-OP(HO)2

That would be the tripolyphosphoric acid, now look at it, the center P is the repeating unit in metaphosphoric acid, all metaphosphoric acid is, is this process reapeating itself until these chains are really long, thereby giving the repeating unit of these polymers.

crackedphosphate.jpg - 39kB

Equipment failure

chloric1 - 8-9-2005 at 15:43

Quote:

Originally posted by BromicAcid
Couldn't copper be used, it is only attacked by sulfuric at high temperatures due to the oxidizing power of that acid at those temperatures, however phosphoric being even less oxidizing should work for this. Copper endcaps for pipe work are highly avalible, I will try to boil down phosphoric acid in copper on Tuesday unless someone else gives it a shot first.

You would think that a copper would hold up but...BIG but here. Thinking nickel was less easily corroded than copper even though it is able to displace hydrogen, I decided on trying to heat the acid in this. Whoa! Big mistake. As soon as it reached boiling temp it was green turning yellow. then the liquid turned orange red upon further heating. Finally as I removed the flame to see if it would solidify, the phosphoric acid had eaten all the way through!! Well, that was $11 wasted. Nickel crucibles are still easy to come buy so I will buy another. I can't figure out the reddish color except I remember reading certain trivalent nickel complexes are red. any thoughts on this? So, I guess I can try copper but I am quite doubtfull. Looks like quartz is the only option.

DSCN1886.JPG - 581kB

red oxidation product

chloric1 - 8-9-2005 at 15:45

I have a couple pics coming

DSCN1888.JPG - 712kB

crucible failure

chloric1 - 8-9-2005 at 15:47

Cannot believe this! A weak acid tearing up nickel!

DSCN1891.JPG - 646kB

BromicAcid - 8-9-2005 at 18:21

Jeeze.... terrible, I would have never expected it. The outlook for copper doesn't look good either, I looked up the resistance of copper and other alloys online to phosphoric acid at 120C and 75% concentration and none of them were really good (except an aluminum/copper alloy), copper wasn't even listed as having a good resistance at room temperature but I will still try it.

Recently I was looking through the "Complete Treatise of Chemistry" series at the entry for metaphosphoric acid and it states that gold is the prefered crucible material of choice for this reacion and that it is prefered as even platinum is attacked! It also lists several forms of metaphosphoric acid that can be made and the preparation of each, listing the metaphosphoric acid generated by heating orthophosphoric acid to red heat and hold it there as having the greatest dehydrating power.

I bought some naval jelly (at great expense) and I will try to do some things with copper and maybe some other metals but the outlook is not good.

12AX7 - 8-9-2005 at 19:35

If you can pour it out while glowing (it's like fused glass, right?), I don't see why a ceramic crucible wouldn't work. If silica isn't soluble, I doubt aluminosilicates would be very soluble. High-alumina crucibles should have less shrinkage than the acid, too, preventing cracking.

Tim

hehhehehe

chloric1 - 8-9-2005 at 20:10

Oh Bromic-I didn't include the juicy pictures yet! Wait until you see light come through the bottom of the crucible. This after rinsing out 2 or 3 grams of nickel phosphates with 31% HCl!! I was flabbergasted by how close I came from the bottom from falling out completely and possibly splashing 250 degree acid everywhere.!

Stay tuned!!1

P.S. Oddly enough my aluminum support ring got a white crust from spatter that rinsed off with water. Maybe aluminum? If not surely aluminum oxide crucibles. I might be suicidel enough to try aluminum metal. But no red heat for the metal. It melts at like 660 C.

another snag

chloric1 - 10-9-2005 at 08:11

well I tried another expensive crucbile. an aluminum oxide one. put in about 50ml of 85 % phosphoric acid in the crucible and then applied a propane flame. it cracked loudly instantly! OK this research has set me back $25 now so now I will only use pyrex or fused silica. I am heating 100ml pf the acid in a pyrex beaker now. IT is now reaching the boiling point and I will see how well it holds up. I have alos requested my library obtain a couple articles about glass corrosion, phosphorica acid etc. It wil be a couple weeks before I know details.

Garage chemist, as far as the info I was able to read in the articel abstracts, the thickening in quartz would be caused by the formation of silicon phosphate. this would also explain about using hot NaOH solution as a remedy for this. FOr this would remove this crusty deposit.

Ahh! the acid looks good and is in rapid embolution! :cool:

COME ON BEAKER YOU CAN DEWWIT!

ADP - 10-9-2005 at 08:18

Good luck with that chloric. What about a carbon graphite crucible?

chloric1 - 10-9-2005 at 08:38

Yes up to 275 degrees C if I can recall. BUt I would make sure it is PURE graphite and not that clay bonded shit. Also, if you can use a kiln,which I cannot, I ve seen lots of article abstracts using alumnium phosphate as a binder in ceramics. Just a thought. hot phosphoric acid bubbeles a little on concrete but mostly becuase of included carbonate. Pure calcium aluminosilicate as a binder for a graohite or better silicon carbide?? I do not know what will work. Right now pyrex works.

Status update. I have not reduced the flame or moved anything and the boiling has slowed down almost entirely. I see period phosphoric acid smoke rise but no major smoking, bumping etc. The beaker is crystal clear and no silicon phosphate can be observed.I have a reduction in fluidic volume of less than 20 % so far. I will wait 20 minutes so the beaker has time to acclimate to its warm environment then I will slightly increase the heat.

12AX7 - 10-9-2005 at 08:51

What th.?! Alumina is one of the strongest ceramics and it has high conductivity and low expansion. I refuse to believe you cracked it!

Geez, you must've used an oxyacetylene torch at least!?

Tim

no only propane

chloric1 - 10-9-2005 at 09:38

I think these are just not designed for liquids. I think the heating alumina and the cool acid just did not agree. Well, the pryex seems to still be working. I know have a crystaline solid in a VERY thick liquid. I cranked up the heat. wish me luck!

LMAO

chloric1 - 10-9-2005 at 10:13

A bug had fallen into my evil phosphoric acid stew and from what my digital thermometer says it is about 520 degrees F or about 270C. Not exactly sure I do not have a Celcius measureing device that goes to 300C :mad:

But the bug kinda melted and carbonized!

Both from the heat and maybe the dehydrating solution. I just am getting so crazy that I find it amusing an insect flew to its grizzly demise in my hot polyacid!

[Edited on 9/10/2005 by chloric1]

Nicodem - 10-9-2005 at 10:42

Like I already said before I have some doubts the metaphosphoric acid could form as low as at 270°C. As already mentioned I heated at an only somewhat lower temperature for 3h under aspirator vacuum and at the end the water was distilling off at a too low speed to be worthy continuing. After weighting the flask the content was practically the theoretical one expected for H4P2O7. So the decomposition ends at the pyrophosphoric acid unless going considerably more extreme. Also without vacuum it seams unlikely the water vapors would be removed faster than they would be readsorbed (unless one really goes to red glowing heat!). To loose more water at a practical speed it seams to me one has to heat at considerably more extreme conditions - perhaps it would get practical at >350°C under vacuum - but that is already more than I would like my flasks to withstand.

[Edited on 10-9-2005 by Nicodem]

simply RED - 10-9-2005 at 14:22

Is silicon phosphate soluble in any phosphoric acid?

chloric1 - 11-9-2005 at 06:22

Nicoderm I believe your right I believe the crystaline material I have is the pyrophosphoric acid. Curiosity aside, I will put a few grams on my pure graphite plate and blast it with my torch. I want to see if I get a glassy material or whatever.

S.C. Wack - 12-9-2005 at 22:33

I took a look in the large P supplement of Mellor's vol 8 today. There were a lot of refs but of course the English-language ones on hand were not so interesting, so I'll paraphrase the book, accurate or not.

Au and Pt are the preferred dehydration crucibles...what a surprise. A small amount dissolves, enough to color the acid. Graphite is OK up to 350C, at which point reduction starts. Hastelloy [nonspecific] crucibles were recommended. These were the only materials mentioned specifically as being OK at high temps. There was an IEC article [23, 140 (1931)] on corrosion but this seems to be at less extreme service. Quite a few alloys were tested.

Impurities increase the level of attack.

There is much mention of glass and silica, though quartz is supposed to be the most resistant. H3PO4 concentrations <60% or something are supposed to be OK, but Pyrex/borosilicates are said to be attacked at pyrophosphoric temps. Some soda glasses are more resistant than others, it says. Some glasses form a dissolved silicon phosphate, others get a protective layer.

One reference is summed up by saying that monoammonium phosphate becomes pyrophosphoric acid after heating at 340C for 3 hours. Polyphosphoric acid is formed at 440C, and higher polyacids at higher temps. Also mentioned is that there is no metaphosphoric acid, just mixtures.

I'll take a look at Gmelin's and the available German articles eventually.

[Edited on 13-9-2005 by S.C. Wack]

Mumbles - 13-9-2005 at 09:06

Have any of you tried to extract the phosphoric acid after heating and separating the different phosphoric acids? Perhaps by calculating how much(if any) metaphosphoric acid one produced you can more accuratly find a correct heat and time.

I got bored so I didn't a little searching here, and came up with a separation proceedure.

Quote:

At the
end of the time allowed for reaction, barium chloride solution
was added to precipitate barium metaphosphate,
which was filtered. To the filtrate ammonium hydroxide
was added to precipitate barium orthophosphate.
Filtration was carried on by suction through a 5.5-cm.
filter in a Biichner funnel. The precipitate was washed
several times with water, then twice with 95% ethyl alcohol,
and finally twice with ether.

Quote:

Separation of these two acids was accomplished by the
procedure of adding barium chloride and ammonium hydroxide,
respectively, to precipitate in turn barium metaphosphate
and barium pyrophosphate.

I had to post the first quote to share the proceedure. The article also says that Metaphosphoric acid was prepared from 85% U. S. P. phosphoric acid by evaporating and finally heating it to a dull red heat for a few minutes. It doesn't mention any sort of crucible material, and I am sure it is nothing you havn't heard yet.

This came from
D. E. Hull;
J. Am. Chem. Soc.; 1941; 63(5); 1269-1272

As far as I can tell copper works.

BromicAcid - 13-9-2005 at 15:02

I made two attempts at metaphosphoric acid today. My first attempt involved naval jelly, which I procured from the hardware store, according to the household products database it is composed of the following:

Quote:

Surfacants 1-3%
Isopropanol 1-3%
Phosphoric Acid 25-30%
Sulfuric Acid 0.1-1%
Water 65-70%
Xynthan Gum 1-3%
Fumed Silica 0.1-1%

So I put that liquid into a copper crucible made by drilling some holes in a large diameter copper endcap. The naval jelly was a bright pink color. I heated cautiously, lots of bubbling started really quickly so I stirred with a graphite rod so that if the bottom was being erroded quickly I would be able to feel it. But it just kept dehydrating and loosing more water. Eventaully it took on a coppery color and I stopped heating. Let it cool and rinsed out the crucible. As far as I could tell it looked great, no pitting, no thin spots, very clean, I guess it only attacked the copper oxide on the inside. So I put more naval jelly into the crucible. And heated with a torch for almost an hour. What I ended up with was a black thick liquid, that when allowed to cool on the stirring rod turned into a reflective glass. When the crucible was cleaned out I noticed no attack though the crucible was oxidized somewhat heavily on the outside, a black flakey film all over it. The first picture in the attached picture is the inside of the crucible after the test run to see if the acid was attacking it, the second picture is just before I shut it off on the second run (notice the color of the crucible and additionally the blackness of the acid is likely due to the organic additives breaking down and such).

My next try at metaphosphoric acid involved heating ammonium phosphate until it completely decomposed. So I put that into the crucible and it was not until it started evolving corpious amounts of ammonia did I remember copper's weakness for ammonia gas. But I pressed on, lots of ammonia being evolved and suddenly (within 5 seconds) it completely stopped. The bottom of the crucible contents solidified and there was no gas evolution. Then shortly after that there was evolution of nitrogen dioxide from the nitrates and such in the fertilizer [Duh.... nitrates and phosphoric acid in a copper crucible, real smart Bromic!] So that died down and the solid shell that had formed melted and I was left with a black liquid. I heated this driving off gasses of all kinds until it would readily solidify upon pulling the stirring rod out of the liquid. I poured it out onto a steel plate and when it solidified it looked just like silver metal, very reflective. When broken it was black in the middle and looked like glass. Adding a piece to water lead to slow dissolution and coloring the water green (iron compounds present in the fertilizer and a nickel stirring rod and copper crucible, take your guess where the color comes from). Slow dissolution is a property of metaphosphoric acid, at least some variaties.

Nothing definate today except as far as I can tell a copper crucible will get you through dehydrating the acid. No attack seen on it except when nitrates are present.

scimadpostpic.jpg - 103kB

chloric1 - 13-9-2005 at 19:06

Bromic, I appreciate the help on this research. after my calamities, I needed a little break. I have some pictures of a very syruppy pyroacid that got hot on mixing an equal volume of silfuric acid. I have the mix in a glass stoppered bottle until later. Sunday I could not get it hot enough to give off SO3 and I was really paranoid about busting the flask and getting burnt. I want to construct a sand bath first and retry with a stronger fire.

Second, I have Reagent grade phosphoric acid I purchased when I had money and I will try copper to get the goods on what really happens. Also, a small sheet of Hastelloy from Mcmaster Carr could be beaten into a homebrew crucible.

Thanks again for your valuable input :cool:

Fleaker - 14-9-2005 at 18:24

Perhaps we (meaning anyone who feels up to it) could try plating a cheap crucible with pure gold since it was mentioned that a gold crucible is preferred. Since solid gold is out of the question, why not plate? I don't think it would cost more than $10 in Au assuming you have the crucible and the necessary reagents. I'm thinking a cyano-gold complex for electroplating the crucible; I'll have to look around and see what they use in industry for making cheap electroplated jewelry.

I've a couple hundred mLs of 85% phosphoric acid, but I'll wait till I can obtain either platinum labware or gold plate a crucible. Do you think heating it in a helium atmosphere would be beneficial? Seems to be rather hygroscopic and blowing helium over it would remove water vapor and prevent any contamination.

Oh Tim, FYI, pure alumina cracks very easily when you take a flame to it; gradual heating works best with alumina labware.

ADP - 18-9-2005 at 15:34

Could a zirconia crucible be feasibly used?

Fleaker - 19-9-2005 at 15:38

I'm guessing it could be used yet it might react with the binding material in the zirconia crucible itself (zirconium oxide, plus something to hold it together).

This weekend I plan on trying this experiment using a copper end cap that I will electroplate with a reasonable thickness of fine gold. I hope to get some pictures, perhaps even video of the subsequent heating and hopefully the product formed

ADP - 19-9-2005 at 16:59

Very nice. Can't wait to hear the results but it seems that a non-reactive metal route would prove more successful. I definately want to attept as (HPO3)n will prove to be very valuble.

Cu is resistant!.

markgollum - 13-10-2005 at 19:39

Alright, yesterday I bought a copper end cap and 4L of concrete etchant.
The etchant/cleaner listed phosphoric acid and dietheleneglycol-monobutyl ether as the only ingredients.
When I got home from the store I poured 80mL of the clear etchant into a 100ml beaker and proceeded to heat it on my hot plate. The etchant frothed and bumped badly at 110°C so I added a few small pieces of gravel which stopped the bumping. However, the frothing continued to get worse until at about120°C, when it overflowed the beaker, hissing and turning black upon contacting the hotplate. Fortunately the ceramic top of my hotplate resisted the hot phosphoric very well so it only suffered minimal damage (about .25 mm was eaten through).
After cleaning everything, I re-attempted to dehydrate 60mL etchant in an 80mL beaker. This time with gentle heating and 3 layers of Al foil on the hot plate. This resulted in the foam overflowing the beaker again, however the Al foil kept the hot plate from damage.
Next I added 50mL etchant to a 300mL beaker and repeated the process, again with fresh Al foil. The phosphoric acid foamed up to the 225mL mark but gradually subsided at 170°C.
The heat was cranked up and the blackening phosphoric acid mixture started to boil gently with no frothing while the temperature rapidly rose. At 340°C I removed the thermometer and let the black liquid gradually cool to room temp. Next I added approx 20mL of the black , syrupy liquid to the copper end cap, placed the cap on my hotplate (with Al foil) and set the heat to max.
The temp rapidly increased to 340°C at which point I removed the thermometer, about 5-7 min after that, the black liquid began to boil again and parts of my hotplate started to glow a dull red .
I was worried about my hotplate so I lowered the heat slightly, but the glowing areas continued to grow and the phosphoric acid bubbled over. When I saw the end cap overflow I knocked it off the hotplate and into the gravel with a board I had handy.
I washed the copper cap and there were no signs of any form of attack, different from what atmospheric oxygen does to copper at those temps.
In conclusion, I believe that copper is sufficiently resistant to phosphoric acid for practical use. By the way, P2O5 can dehydrate amides to nitriles.

CD-ROM-LAUFWERK - 14-10-2005 at 06:39

yes Cu is resistant, but there are signs of attack!
it turned dark when the HPO3 came in contakt whit the Cu, so it must be a passivation

the layer of passivatet Cu dont dissolve in water (just as an information, so u can clean the equipment whit warer

)
if the H3PO4 alredy turned into pyrophosphoric acid and the same start to turn into HPO3 the stuff is that viscous that droplets start to spray out, so be careful

BromicAcid - 14-10-2005 at 20:17

Indeed, there is attack. Although the crucible itself didn't look like it was attacked significantly, upon dissolution of some of the resulting solid metaphosphate in water I found there was an insoluble white component (copper I compounds? polymetric phosphoric acids?) and there was also a bit of what looked like elemental copper powder at the bottom of the test tube, and the water was distinctly blue. Attached is a picture of what I got upon dissolving about 3 grams of my obtained solid in water.

Note that although it did react, the crucible looked fine so since the oleum distills it shouldn't be much of a problem... probably...

precipitatephosphate.jpg - 27kB

nitroglycol - 30-11-2007 at 18:10

Quote:

Originally posted by chloric1
A bug had fallen into my evil phosphoric acid stew and from what my digital thermometer says it is about 520 degrees F or about 270C. Not exactly sure I do not have a Celcius measureing device that goes to 300C :mad:

But the bug kinda melted and carbonized!

Both from the heat and maybe the dehydrating solution. I just am getting so crazy that I find it amusing an insect flew to its grizzly demise in my hot polyacid!

I guess that would be a bit of a fly in the ointment...

ADP - 19-5-2008 at 21:15

This compound really intrigues me, I wish I still had my 500mL of ACS H3PO4 however I disposed of it when I went to college. I'd really like to experiment with this compound again this summer.

Jor - 20-5-2008 at 00:20

Just bought 100g of metaphosphoric acid, for 8 british pounds

This seller is awesome:
http://myworld.ebay.co.uk/mordants-2008/

ADP - 20-5-2008 at 06:13

Nice find!

Jor - 20-5-2008 at 07:17

I just ordered the 100g metaphosphoric acid from Aldrich before posting the link. Otherwise it would be gone in a few minutes

According to item description, it is 33,5-36,5% metaphosphoric acid, stabilized with >65% sodium metaphosphate. Why do they stabilize it? Does it still have the powerfull dehydrating properties then?

LSD25 - 21-5-2008 at 23:39

Quote:

Originally posted by Jor
Just bought 100g of metaphosphoric acid, for 8 british pounds

This seller is awesome:
http://myworld.ebay.co.uk/mordants-2008/

Yeah, they were - unfortunately as of this time they are no longer offering ANY items for sale, which is kind of a change from what they had on offer for the last couple of weeks :mad:

Fluorite - 1-5-2021 at 09:09

How does sulfuric monochloride react with phosphoric acid? Can it be used to dehydrate it at room temperature?

njl - 1-5-2021 at 12:37

You're gonna have to elaborate on "sulfuric monochloride". Do you mean chlorosulfuric acid? Or disulfur dichloride?

Fluorite - 1-5-2021 at 12:42

Sorry I meant disulfur dichloride

njl - 1-5-2021 at 14:28

Alright, well I really doubt anyone here can answer from experience. In all likelihood the answer is yes, but what the phosphoric acid is dehydrated to I couldn't say. Probably won't work exactly how the dehydration of acetate does. Something will be dehydrated but perhaps not in the way that you want.

edit: I just realized how old this thread is. Also, would there even be an advantage to dehydrate with S2Cl2?

[Edited on 5-1-2021 by njl]

chloric1 - 15-6-2023 at 08:59

https://cdnsciencepub.com/doi/pdf/10.1139/v56-102

This is an interesting and informative 13 page article regarding “the strong phosphoric acid‘s “their synthesis in their properties.

Interesting to note that no cyclic phosphoric acids detected. They made them by heating the required amount of P2O5 with 85% orthophosphoric acid to 350 Celsius. They s process is a lower temperature method so they are able to stop reaction right when the acids start to attack the Pyrex container

chornedsnorkack - 16-6-2023 at 07:02

Quote: Originally posted by chloric1

https://cdnsciencepub.com/doi/pdf/10.1139/v56-102

This is an interesting and informative 13 page article regarding “the strong phosphoric acid‘s “their synthesis in their properties.

Interesting to note that no cyclic phosphoric acids detected.

And no branched acids.
They suggest, reference to link 40 (van Wazer, Holst 1950) that branched acids should promptly decompose in "all solvents".
On what grounds?
Decomposition of a branched acid is still breaking a P-O-P bond. It may be easier than in a straight or cyclic acid but it is sluggish even in cold water.
Their solvents do contain water - something which favours hydrolysis, sluggish as it is. And the rest is alcohol (isopropanol) - also capable of forming phosphate esters and in the process releasing water and breaking P-O-P bonds.

Could you dissolve phosphoric acids in a solvent which has no mobile hydrogens, no way to free water on reaction and difficulties attacking bonds?
Like triethylamine?
Looks like a convenient solvent. Boils at +89 C. Freezes at -115 C.
Is triethylamine a good solvent for its salts?

clearly_not_atara - 20-6-2023 at 13:18

Quote: Originally posted by chloric1

When an article from 50 years ago disagrees with ideas that are still held today, it is possible that we have been mistaken for decades, but it is also possible that the article is itself mistaken. In this case, it seems to be the latter; the cyclic structure was detected by Chakarawet et al via crystallization and protonation of salts with bis(triphenylphosphanyl)iminium:

"Crystalline Metaphosphate Acid Salts: Synthesis in Organic Media,
Structures, Hydrogen-Bonding Capability, and Implication of
Superacidity": https://drive.google.com/file/d/1joJWfWU_YhE-VWbGISAi0S7Jvva...

Notably, one inference derived in the above publication is that H3P3O9 is of comparable strength, and possibly stronger, than TfOH (!). This gives some clarity to the question of why it is so noxiously corrosive to its containers.

chornedsnorkack - 20-6-2023 at 19:39

Quote: Originally posted by clearly_not_atara

This is an interesting and novel claim.
The systems of P2O5-hygroscopic superacid should be well known because they form a standard synthetic route to the oxides/anhydrides. Has anyone previously noted what form metaphosphoric acids take in, for example, H2S2O7/P2O5 solution?