megalomania
June 21st, 2003, 11:26 AM
Microtek
Frequent Poster
Posts: 205
From:
Registered: JAN 2001
posted 06-28-2001 05:05 AM
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First, let me apologize for what some may see as repetitious, but I think that this deserves specific attention.
In an old chemistry book that I have, it is stated that when acetylene gas is bubbled through acetic acid you get acetic anhydride and acetaldehyde.
This would be a much easier way to get acetic anhydride from 99% acetic acid, and if reasonable amounts of acetaldehyde is produced and could be distilled off....
So the question is: Can you simply bubble acetylene gas through the acetic acid at perhaps 25 degrees and condense the acetaldehyde, or do you need katalysts or certain temps, etc.
PHILOU Zrealone
Frequent Poster
Posts: 479
From: Brussels,Belgium,Europe
Registered: SEP 2000
posted 06-28-2001 07:58 AM
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Let's figure that out...
H-C#C-H + CH3-C(=O)-OH --> H2C=CHOH + CH2=C=O
Basicaly you have a dehydration of acetic acid into ketene and in the same time hydratation of acetylen in vinylic alcohol.
Ketene can react further with an exces molecule of acetic acid to give acetic anhydride.
CH2=C=O + HOCO-CH3 --> CH3-CO-O-CO-CH3
Vinylic alcohol or ethenol/ethylenol is in equilibrium with the more stable isomer (due to enol-ceton equilibrium).
CH2=CHOH <-===> CH3-CH=O (acetaldehyde or ethanal)
Now you can also have some other products depending on the experimental conditions like vinyl acetate CH2=CH-O-CO-CH3 and polyvinylacetate, and ...
My guess is that pressure has to be applied, some heat, some catalyst, and polymerisation inhibitors. I can't tell you more...you'll have to find it out (a little tial?).
------------------
"Life that deadly disease sexually transmitted".
"Chemistry is all what stinks and explode; Physic is all what never works! ;-p :-) :o)"
Microtek
Frequent Poster
Posts: 205
From:
Registered: JAN 2001
posted 06-28-2001 05:00 PM
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I tried simply bubbling the acetylene through the 99% acetic acid. No cooling, no heating, no catalyst and no success...
After having passed the acetylene through for 30 min, I tried cooling the liquid down to see if it froze, since glacial acetic acid freezes at ca. 15 C and the anhydride at ca. -70.
At first, I thought that it had worked as I got to ca. 5 C and it was still liquid, but when I decreased the temp to -18 C it froze solid.
Is it concievable that there was some anhydride in it, or does the two ( acetic acid/anhydride ) not coexist?
Mr Cool
Frequent Poster
Posts: 991
From: None of your bloody business!
Registered: DEC 2000
posted 06-29-2001 04:52 PM
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They must be able to coexist, otherwise you couldn't make acetic anhydride by bubbling ketane or whatever it is through acetic acid, since it can't all be converted at once so at some point there must be a mixture of the two.
I'd guess that you'd need heat to make the reaction proceed (or at least at a reasonable rate), pressure to stop anything boiling away, maybe polymerisation inhibitors since things tend to polymerise faster at higher temperatures (like all reactions), and maybe a few catalysts to help it along.
But if you got the mixture down to -18*C, then it can't be just acetic acid anymore...
How does it smell? Does it burn? If so, how well? Does it heat up on contact with water? How acidic is it?
Oh, and I'd be careful about bubbling acetylene into you house for 30 minutes! (I'm assuming you did it outside, right?)
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-29-2001 05:45 PM
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I'd also be careful about using too much pressure with acetylene - from what I understand, the maximum pressure permissible with the dry gas is about 30 psi; any higher and it self-combusts. I don't know, but applying heat might lower this point. The 300 psi acetylene in tanks is achieved by driving it into solution in acetone (that's why acetylene tanks are so heavy), but I think any attempt to pressurize acetylene directly is asking for trouble. This would almost certainly be the case in a sealed reaction vessel.
Very interesting possibilities though, and I agree that the depressed freezing point is evidence that *some* change has taken place. I wonder if (instead of bubbling) one could calculate the amount of acetylene needed to completely react with a given amount of acid, seal those quantities in a chamber and shake hell out of it for a few hours (for example with a paint shaker). A process like that would certainly encourage more complete reaction, assuming reaction pressures remained within safe limits. Another possibility might be to use an ultrasonic atomizer (humidifier type) to spew a microfine acetic acid mist into an atmosphere of acetylene (in a closed chamber). Not exactly a vapor phase reaction, I know, but ought to provide ample opportunity for the reactants to come into intimate contact.
John456
Frequent Poster
Posts: 105
From:
Registered: MAR 2001
posted 06-29-2001 10:01 PM
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Heres what i did: I took one of those vacuum trap jars (the kind with the vacuum connector at the bottom of the jar and the stopper with 2 connections, one for a vacuum and one for a bubbler) and connected an acetylene generator (an ehrlenmeyer flask with calcium carbonate and water) and left the vacuum connector one open. The idea was for the aquarium pump to create a sort of acetic acid mist so the acetylene gas would touch more of the acid. After half an hour of bubbling the acetylene i took it off the generator and poured the product into a beaker. First i tested the flammability (apparently none at all) and then i took 10ml of it and added it to 5ml of water and it got a little warm but not much warmer than it was. When i was bubbling the gas in it did get notibly warmer though. Then i tried freezing it and it froze at about 5*C. PURE acetic acid and acetic anhydride can coexist but the presence of any water will convert the anhydride back into acid. What i think is happening is some vaporized water is coming over with the acetylene gas and thats causing any anhydride converted to convert back to acetic acid. Perhaps drying the acetylene will solve this problem? Does anyone know how to dry it? Calcium chloride might react with the gas to form calcium carbide again so i dont think that would work. Possibly calcium oxide?
PHILOU Zrealone
Frequent Poster
Posts: 479
From: Brussels,Belgium,Europe
Registered: SEP 2000
posted 07-04-2001 08:45 AM
--------------------------------------------------------------------------------
Microtek:
Two liquids mixed together have a lower melting point than the original products...that's cald cryoscopic lowering of the MP...an impure product has a lower MP than the original pur product even if the impurity has a higher MP.
So with a MP of 18 instead of 15, I would say it is only your glacial H-AC being in overmelting!
------------------
"Life that deadly disease sexually transmitted".
"Chemistry is all what stinks and explode; Physic is all what never works! ;-p :-) :o)"
deezs
Frequent Poster
Posts: 113
From: Hungary
Registered: MAY 2001
posted 07-04-2001 02:23 PM
--------------------------------------------------------------------------------
I have read somewhere, that clear acetic acid, containing just about 1% water, freezes at 5 deg. (it melts again at 16 deg.)
Frequent Poster
Posts: 205
From:
Registered: JAN 2001
posted 06-28-2001 05:05 AM
--------------------------------------------------------------------------------
First, let me apologize for what some may see as repetitious, but I think that this deserves specific attention.
In an old chemistry book that I have, it is stated that when acetylene gas is bubbled through acetic acid you get acetic anhydride and acetaldehyde.
This would be a much easier way to get acetic anhydride from 99% acetic acid, and if reasonable amounts of acetaldehyde is produced and could be distilled off....
So the question is: Can you simply bubble acetylene gas through the acetic acid at perhaps 25 degrees and condense the acetaldehyde, or do you need katalysts or certain temps, etc.
PHILOU Zrealone
Frequent Poster
Posts: 479
From: Brussels,Belgium,Europe
Registered: SEP 2000
posted 06-28-2001 07:58 AM
--------------------------------------------------------------------------------
Let's figure that out...
H-C#C-H + CH3-C(=O)-OH --> H2C=CHOH + CH2=C=O
Basicaly you have a dehydration of acetic acid into ketene and in the same time hydratation of acetylen in vinylic alcohol.
Ketene can react further with an exces molecule of acetic acid to give acetic anhydride.
CH2=C=O + HOCO-CH3 --> CH3-CO-O-CO-CH3
Vinylic alcohol or ethenol/ethylenol is in equilibrium with the more stable isomer (due to enol-ceton equilibrium).
CH2=CHOH <-===> CH3-CH=O (acetaldehyde or ethanal)
Now you can also have some other products depending on the experimental conditions like vinyl acetate CH2=CH-O-CO-CH3 and polyvinylacetate, and ...
My guess is that pressure has to be applied, some heat, some catalyst, and polymerisation inhibitors. I can't tell you more...you'll have to find it out (a little tial?).
------------------
"Life that deadly disease sexually transmitted".
"Chemistry is all what stinks and explode; Physic is all what never works! ;-p :-) :o)"
Microtek
Frequent Poster
Posts: 205
From:
Registered: JAN 2001
posted 06-28-2001 05:00 PM
--------------------------------------------------------------------------------
I tried simply bubbling the acetylene through the 99% acetic acid. No cooling, no heating, no catalyst and no success...
After having passed the acetylene through for 30 min, I tried cooling the liquid down to see if it froze, since glacial acetic acid freezes at ca. 15 C and the anhydride at ca. -70.
At first, I thought that it had worked as I got to ca. 5 C and it was still liquid, but when I decreased the temp to -18 C it froze solid.
Is it concievable that there was some anhydride in it, or does the two ( acetic acid/anhydride ) not coexist?
Mr Cool
Frequent Poster
Posts: 991
From: None of your bloody business!
Registered: DEC 2000
posted 06-29-2001 04:52 PM
--------------------------------------------------------------------------------
They must be able to coexist, otherwise you couldn't make acetic anhydride by bubbling ketane or whatever it is through acetic acid, since it can't all be converted at once so at some point there must be a mixture of the two.
I'd guess that you'd need heat to make the reaction proceed (or at least at a reasonable rate), pressure to stop anything boiling away, maybe polymerisation inhibitors since things tend to polymerise faster at higher temperatures (like all reactions), and maybe a few catalysts to help it along.
But if you got the mixture down to -18*C, then it can't be just acetic acid anymore...
How does it smell? Does it burn? If so, how well? Does it heat up on contact with water? How acidic is it?
Oh, and I'd be careful about bubbling acetylene into you house for 30 minutes! (I'm assuming you did it outside, right?)
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-29-2001 05:45 PM
--------------------------------------------------------------------------------
I'd also be careful about using too much pressure with acetylene - from what I understand, the maximum pressure permissible with the dry gas is about 30 psi; any higher and it self-combusts. I don't know, but applying heat might lower this point. The 300 psi acetylene in tanks is achieved by driving it into solution in acetone (that's why acetylene tanks are so heavy), but I think any attempt to pressurize acetylene directly is asking for trouble. This would almost certainly be the case in a sealed reaction vessel.
Very interesting possibilities though, and I agree that the depressed freezing point is evidence that *some* change has taken place. I wonder if (instead of bubbling) one could calculate the amount of acetylene needed to completely react with a given amount of acid, seal those quantities in a chamber and shake hell out of it for a few hours (for example with a paint shaker). A process like that would certainly encourage more complete reaction, assuming reaction pressures remained within safe limits. Another possibility might be to use an ultrasonic atomizer (humidifier type) to spew a microfine acetic acid mist into an atmosphere of acetylene (in a closed chamber). Not exactly a vapor phase reaction, I know, but ought to provide ample opportunity for the reactants to come into intimate contact.
John456
Frequent Poster
Posts: 105
From:
Registered: MAR 2001
posted 06-29-2001 10:01 PM
--------------------------------------------------------------------------------
Heres what i did: I took one of those vacuum trap jars (the kind with the vacuum connector at the bottom of the jar and the stopper with 2 connections, one for a vacuum and one for a bubbler) and connected an acetylene generator (an ehrlenmeyer flask with calcium carbonate and water) and left the vacuum connector one open. The idea was for the aquarium pump to create a sort of acetic acid mist so the acetylene gas would touch more of the acid. After half an hour of bubbling the acetylene i took it off the generator and poured the product into a beaker. First i tested the flammability (apparently none at all) and then i took 10ml of it and added it to 5ml of water and it got a little warm but not much warmer than it was. When i was bubbling the gas in it did get notibly warmer though. Then i tried freezing it and it froze at about 5*C. PURE acetic acid and acetic anhydride can coexist but the presence of any water will convert the anhydride back into acid. What i think is happening is some vaporized water is coming over with the acetylene gas and thats causing any anhydride converted to convert back to acetic acid. Perhaps drying the acetylene will solve this problem? Does anyone know how to dry it? Calcium chloride might react with the gas to form calcium carbide again so i dont think that would work. Possibly calcium oxide?
PHILOU Zrealone
Frequent Poster
Posts: 479
From: Brussels,Belgium,Europe
Registered: SEP 2000
posted 07-04-2001 08:45 AM
--------------------------------------------------------------------------------
Microtek:
Two liquids mixed together have a lower melting point than the original products...that's cald cryoscopic lowering of the MP...an impure product has a lower MP than the original pur product even if the impurity has a higher MP.
So with a MP of 18 instead of 15, I would say it is only your glacial H-AC being in overmelting!
------------------
"Life that deadly disease sexually transmitted".
"Chemistry is all what stinks and explode; Physic is all what never works! ;-p :-) :o)"
deezs
Frequent Poster
Posts: 113
From: Hungary
Registered: MAY 2001
posted 07-04-2001 02:23 PM
--------------------------------------------------------------------------------
I have read somewhere, that clear acetic acid, containing just about 1% water, freezes at 5 deg. (it melts again at 16 deg.)