Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Metaphosphoric Acid Impregnated onto Pumice
I am going to try and replicate an old procedure that uses "glacial phosphoric acid" on pumice as catalyst for dehydration of an alcohol.
I have determined that glacial phosphoric acid is metaphosphoric acid. This is usually sold in stick form.
So how to I load the metaphosphoric acid onto the pumice pieces?
Only thing I can think of is to place the sticks and the pumice pieces in a ball mill and wait while the stones go to work on the acid sticks.
Metaphosphoric acid is supposed to volatilize at red heat, Usually this is dine in a platinum crucible, sorry, all out of large platinum crucibles
here, or small ones for that matter.
Anyone have any bright ideas?
Sic gorgeamus a los subjectatus nunc.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Remembering phosphoric acid dehydrates to a glassy solid, wouldn't it serve to soak them in phosphoric acid and cook it? Not going so hot as to fuse
the HPO3 and SiO2 + stuff, of course.
Tim
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Yes, the metaphosphoric acid would obviously be created on the pumice by dehydration of H3PO4.
If I remember correctly it needs to be heated to 150°C in vacuum for 24 hours (not sure about the time). At this temperature the glass is not
attacked and it can be done in an ordinary flask.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
You almost need to check old product lists from druggist/chemical suppliers, as the meaning of "glacial phosphoric acid" changes with time and
country. The paper you refer to is of WW-I vintage, a decade earlier in the US the imported "glacial phosphoric acid" was typically metaphosphoric
acid containing some sodium phosphates to help retain the solid form.
However in the same general time frame laboratory glacial phosphoric acid could be the mix of phosphoric acids made by heating H2PO4 to 120 to 150 C,
and which would solidify in most areas at the typical room temperature.
So the plan to start with ordinary phosphoric acid, absorb it into the pumice, and dehydrate it, would be the best.
It is annoying how chemistry labs of the late 19th and early 20th century at times appear to have had literal piles and stacks of platinum ware, and
would frequently use it.
[Edited on 31-12-2007 by not_important]
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
The problem with ambiguity, of course, is that it is so frigging ambiguous.
Several of the condensed phosphoric acids are glassy solids. Pyrophosphoric acid which is a dimer is a good example.
Metaphosphoric acid is supposed to be (HPO3)n. I have the original paper that decided this based on vapor density studies.
I guess the logical course is to try the simplest approach first. As suggested, acquite pumice pieces of appropriate size, soak them in 85% H3PO4 and
bake them in vacuo till glassy.
In the 1919 J.Che,.Soc. paper it is advised that occasional regeration of the catalyst is a simple matter of letting the P4O10 smoke from a small
piece of WP burning at the mouth of the reaction tube in a current of air, does the job.
That being the case, can I not start with polyphosphoric acid instead of 85% orthophosphoric acid?
PPA is a mixture of condensed phosphoric acids, including metaphosphoric acid, and is not just a solution of P4)10 in anhydrous H3PO4 - in other words
it is not at all analogous to oleum although we tend to think of it that way.
In fact you can make PPA by adding P4O10 to 85% H3PO4.
And that is why we stubbornly tend to think of it like oleum, because trying to sort out the complexities of the myriads of condensed oxyacids of
phosphorus will give one a headache.
I guess roundish 5-6mm pieces of pumice will do. They are going to be used in a 2.2 cm copper tube. A meter and a half long.
It goes without saying that I haven't got any WP to burn to regenerate this catalyst. But as this is likely a one time operation, it does not matter.
My purpose in stressing the regeneration is to point out that the by product of the alcohol dehydration is water and metaphosphoric acid is slowly
changed by water to H3PO4. So P4O10 reacts with th water and then in the heating gets converted back to metaphosphoric acid, I suppose.
[Edited on 31-12-2007 by Sauron]
Sic gorgeamus a los subjectatus nunc.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
I would think polyphosphoric acid would do well, especially if it is cheap and easily accessible.
Part of the ambiguity is the near century difference in terminology, not to mention any regional differences - the old chem books I have run into
that between US, British, and German origins. Even formula don't always help, if the book is old enough water is HO and the atomic weights are
coopered.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
At least the pumice is not a problem. Aldrich has vastly overpriced pumice while Acros is much more reasonable. Acros has granular, 1 to 4 mm.
Slightly smaller than what I contemplated, but if I sieve out the stuff under 3 mm, it ought to be OK.
I took a close look at the fractionation of the dibromides obtained from bubbling th alkenes through Br2. The total residue, which would include any
1,2-dibromobutane formed, was less than 3%. So that is very selective for 2-butene. There was no isobutene at all. The 3% tail would also have
included any polymerized product(s) as well.
Sic gorgeamus a los subjectatus nunc.
|
|
|
JohnWW
International Hazard
Posts: 2849
Registered: 27-7-2004
Location: New Zealand
Member Is Offline
Mood: No Mood
|
|
Here in New Zealand, there are places where pumice (or its compressed form, ignimbrite) can be simply carted away free by the tonne. The stuff is an
eruption product of the rhyolitic (high-silica) volcanoes in the center of the North Island. It is also often found in lumps washed up on beaches,
either as the result of having been washed down rivers or from eruptions from similar under-sea volcanoes.
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
just an idea, and I`m not sure how feasible it is, but couldn`t you mix the pumice with P4O10 both as powders, and the natural moisture from the air
on the pumice will react with the pentoxide to form the acid.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
Ozone
International Hazard
Posts: 1269
Registered: 28-7-2005
Location: Good Olde USA
Member Is Offline
Mood: Integrated
|
|
Happy New year to All,
Hmm. IIRC, we used to make "acidified" Na2SO4 (anh) to use when running EPA 515.1 (herbicides). It seems to me that a similar protocol could be used
with your pumice.
1. Carefully prepare a solution of H2SO4 (use H3PO4) in diethyl ether (with dry ether, your fine).
2. In a large evaporating dish (or pan), the ether mix is slurried with anhydrous Na2SO4 (use pumice).
*I think we might have slurried the Na2SO4 in ether, then added the H2SO4* (evaporation would chill the mixture)
3. Remove the bulk ether by evaporation under forced draught (in hood).
4. Bake the (now dry, check this by crushing a few granules and checking for ether; this I did by smell) mixture for at least 4 hr at 105°C (IIRC).
5. Break up the "brick" with a hammer (take care, the dust is quite...acidic).
6. The larger chunks are brought to desired size with a mortar/pestle.
7. The material is stored in an air-tight jar until needed.
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Thanks, guys.
When I was a kid I used to walk along the rairoad tracks in Audubon park, or maybe it was City Park, New Orleans. The reail bed was chunks of pumice.
Doubtful that it was local, but probably didn't come from NZ either.
I think they still make a hand soap called Lava that is impregnated with fine pumice dust. A bit scratchy and you would not want to use it on body or
face but for dirty hands it is very effective.
Sic gorgeamus a los subjectatus nunc.
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
it`s still used in some exfoliant scrubs in the cosmetics industry, I think The Body Shop do a version for feet.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Here's what Merck has to say about (ortho)phosphoric acid
Becomes anhydr at 150degrees, gradually changes to pyrophosphoric acid at approximately200degrees, and changes to metaphosphoric acid when heated
above 300degrees.
So: if glacial phosphoric acid = metaphosphoric acid, then pumice soaked in 85% H3PO4 then baked at >300 C will be what I want.
If glacial phosphoric acid is simply anhydrous, glassy phosphric acid then 150 C would suffice.
Ordinary phosphoric acid is certainly cheaper than metaphosphoric acid and being liquid no problem to get into all those nice nooks and crannies in
the pumice. O3's suggestion of employing a low boiling solvent vehicle then takeing it off, would ensure better penetration than the syrupy H3PO4
might achieve on its own.
I guess the thorough thing to do is try it both ways and see if the selectivity for the alkenes is same or different.
The ambiguity involved in the name, arises for several reasons as has been discussed. Another one is that H3PO4 supercools to a glass.
However I am betting on the identity intended by the author being metaphosphoric acid. The dehydration of butanol vapor is conducted at 280-400 C and
at that range, H3PO4 is going to change to (HPO3)n anyway.
Chemical vendors sometimes show a formula for polyphosphoric acid of (HPO3)n which is not really the case.
PPA usually analyzes to c.55% tripolyphosphoric acid the the rest, a mix of H3PO4 and various condensed acids. And while H3PO4 converts to
metaphosphoric acid above 300 C, PPA boils at 550 C. So PPA is not a good candidate for my application.
[Edited on 1-1-2008 by Sauron]
Sic gorgeamus a los subjectatus nunc.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
