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Author: Subject: oleum & SO3
Lambda-Eyde
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[*] posted on 20-11-2008 at 05:47


Hello !

I've been searching around this forum a little bit and read the bulk of this thread, but I still haven't found anyone mentioning synthesizing SO3 from potassium polysulfide and H2SO4 ? Just see this wonderful demonstration by Mabakken (I think he goes under the pseudonym "ScienceGeek" here at SM;)) over at Youtube.

Here in Norway potassium polysulfide can be bought mixed with other sulfides of potassium as "Liver of sulfur" at the drugstore. Will these other compunds interfere with the reaction? What's the "worst case scenario"? Getting SO2 together with the SO3?

I'm surprised that I haven't seen this anywhere on the forum; am I missing something vital? Is potassium polysulfide virtually impossible to get ahold of in the US? Looking at the video, the reaction seems fairly straight-forward, provided you have adequate ventilation.

-Cheers
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[*] posted on 20-11-2008 at 07:35


I think what you are refering to is where Mabakkens video of making SO3 using Potassium Persulphate, not polysulphide.
So that is probably the resason you havnt heard us talk about polysulphides. There are however many threads on using persulphates. UTSE!
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[*] posted on 20-11-2008 at 08:03


Welcome to SciMad, Lambda-Eyde. . .
It's a pity about the extensive carbonisation in SG's SO3; he must have used lubricant grease (or glycerin) on joints for that to happen.
Concentrated H2SO4 on joints might have been better.
I don't know if Glindemann rings would be stable at the temps used---if they are (breakdown~260*C) clean SO3 would come over.
IIRC, someone mentioned a putative electrolytic process for oleum preparation, but I can't seem now, to find it.
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[*] posted on 20-11-2008 at 09:08


Anyway, pyrosulphate NaS2O7 from heating the bi-sulphate is a less-costly route than the peroxydisulphate (full whack) one.
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[*] posted on 20-11-2008 at 09:11


Oh dear, my bad. My mind must be playing tricks on me.
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[*] posted on 20-11-2008 at 09:43


It happens everyone. . .
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[*] posted on 16-5-2009 at 10:33
SO3 using P2O5



I got hold of some P2O5, and I was kind of searching what to do with it. I allready used it to make my own rust remover. Works like a charm. :cool:

According to wikipedia:

Quote:

The desiccating power of P4O10 is strong enough to convert many mineral acids to their anhydrides. Examples: HNO3 is converted to N2O5; H2SO4 is converted to SO3; HClO4 is converted to Cl2O7.


I read the same in old chemistry books.

Is it really possible to convert H2SO4 to free oleum using P2O5? I'm really not gonna try this without more detailed information. I've seen actual flames when adding lumps of P2O5 to water. :)

Further, are there any lab methods known that confirm this and/or give an acceptable synthesis?






[Edited on 16-5-2009 by Leander]
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[*] posted on 16-5-2009 at 12:21


Conversion of sulfuric acid to sulfur trioxide by way of phosphorous pentoxide is indeed possible. Check out the thread on oleum production:

http://www.sciencemadness.org/talk/viewthread.php?tid=727

There are examples of using metaphosphoric acid to afford the conversion so phosphorous pentoxide should work like a charm, likely with a bit of heat to allow the separation of the volitile sulfur trioxide.

Although I have not been as active on this forum as of late so there may be more relevant recent posts that someone might be able to point you toward.




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[*] posted on 16-5-2009 at 16:07


I've made SO3 from H2SO4 and P2O5 several times when I didn't have my current equipment (tube furnace) available.
Mix 75ml conc. H2SO4 with 100g P2O5 in a round-bottom flask by shaking, let it stand tightly closed for 1-2 days and then distill the mixture over a free flame (strong heat is necessary).
SO3 collects as a distillate. Cool the receiver with ice, and don't use any water in the condenser, otherwise the danger of clogging
due to crystallizing SO3 exists (still, watch out for this!).
The procedure has to be done under a fume hood, like everything involving SO3.

This method has been developed by members of the german forum, I don't know where you could find a method in literature, but let me assure you that the above method does work.

Both oleum and solid SO3 can be directly converted to chlorosulfonic acid by gassing them with dry HCl. The reaction is very exothermic and rapidly melts the solid SO3.
Then the mixture is distilled to seperate ClSO3H from any H2SO4.




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16-5-2009 at 17:09
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[*] posted on 17-5-2009 at 04:09


That sounds really great! :)

I didn't mentioned that my goal is to get oleum for the production of several nitroaromatics such as TNT. It wouldn't be strait forward at all to distill the product, and put myself in danger trying to obtain pure SO3, simply to add it to sulphuric acid again.

I haven't got any experience myself using H3PO4 in mixed acids. According to urbanski (Vol II, p341) nitration of cellulose by mixed acids containing H3PO4 gave better results then using H2SO4/HNO3, and a Nitrogen % of 14%. :)

H3PO4 doesn't hydrolyses the product as H2SO4 does, giving better yields and a more stable product. The only drawback is the fact that phosphoric acid can't absorb water as H2SO4 does. Therefore only mixtures with nearly zero H2O content or even free P2O5 are useful. As a result of that P2O5/HNO3 mixtures are not really interesting IMO. Also a lack of references using this method doesn't really encourages me.

Since aromatics are probably not bothered at all by mixed acids containing small amounts of phosphoric acid, wouldn't it be possible to use H2SO4/P2O5 strait away? The only danger I could think of is the formation of nitric anhydrides, when P2O5 is used in excess, but that's fixed by using proper molar ratio's. Further, the reaction rate might slow down a little.

Any idea's?:cool:












[Edited on 17-5-2009 by Leander]
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[*] posted on 17-5-2009 at 05:33


I dont think phosphoric acid is strong enough to protonate the nitric and thus allow water to leave forming the nitronium ion (the electrophile in nitration reactions). H2SO4 has a pKa ~-2, whereas H3PO4 has a pKa ~ 3 (according to paulings rules).I think nitric acid should be somewhere between the two. Therefore I would expect P2O5 and HNO3 mixtures to be poor nitrating agents (except from the increased concentration of the nitric acid due to removal of the azeotropic (~32%) water by the P2O5).
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[*] posted on 17-5-2009 at 17:22


No, I don't think this will work, since the P2O5/H2SO4 mix does not seem to contain any free SO3 at room temperature- it doesn't even fume in air! I think it contains mixed anhydrides of H2SO4 and H3PO4 instead.
The SO3 is only liberated upon strongly heating the mixture- despite the 45°C boiling point of monomeric SO3, the mixture must be heated far above 200°C to liberate most of its SO3. This strongly suggests that the SO3 is produced by some sort of pyrolysis process in the mixture instead of just being distilled out.

Also, the P2O5/H2SO4 mix is very viscous. You would have a hard time nitrating anything with it.
You should really try to make pure SO3 and add this to H2SO4.




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[*] posted on 17-5-2009 at 17:58


Quote: Originally posted by DJF90  
I dont think phosphoric acid is strong enough to protonate the nitric and thus allow water to leave forming the nitronium ion (the electrophile in nitration reactions). H2SO4 has a pKa ~-2, whereas H3PO4 has a pKa ~ 3 (according to paulings rules).I think nitric acid should be somewhere between the two. Therefore I would expect P2O5 and HNO3 mixtures to be poor nitrating agents (except from the increased concentration of the nitric acid due to removal of the azeotropic (~32%) water by the P2O5).


IIRC, you will generate some N2O5, which behaves as nitronium nitrate. The nitrating properties will differ from normal mixed acids, I imagine.

[Edited on 5-18-09 by UnintentionalChaos]




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[*] posted on 17-5-2009 at 19:10


Yes of course but only if there is excess P2O5. The [NO2][NO3] will of course be an effective nitrating agent, and if I'm doing the mechanism right in my head then HNO3 is the byproduct.
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[*] posted on 7-1-2010 at 09:41
Oxidising sulphur dioxide


How can someone turn sulphur dioxide into trioxide without using high pressure vessels or huge deals of heat (>400 ºC)?

Best regards, Dúlio.

[Edited on 7-1-2010 by D S2 A]




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[*] posted on 7-1-2010 at 11:05


Read the fucking thread!!!
Pass over V2O5 mixed with O2...
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[*] posted on 7-1-2010 at 11:11
Ops!


Sorry. I forgot to mention that vanadium pentoxide is not available here... :D

Any suggestions?

Best regards, Dúlio.




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[*] posted on 7-1-2010 at 11:13


Other catalyst, do some research!!!!






Hint - Fe2O3
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[*] posted on 7-1-2010 at 11:15


Thank you, Picric-A . Do you have any other hint? Ferric oxide is not very efficient...

Best regards, Dúlio.




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[*] posted on 7-1-2010 at 11:15


No, do some work yourself.

[Edited on 7-1-2010 by Picric-A]
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[*] posted on 7-1-2010 at 11:19


I am doing that since a few hours ago. Thank you for the attention, Picric-A. In case of any good information: [ dulio@vista.aero ].

Best regards, Dúlio.




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[*] posted on 7-1-2010 at 11:21


Thats obviously wrong as i did one google search now, 'oxidation of SO2' and it came up with a very good catalyst, oxidises efficiently, quickly with good yield.
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[*] posted on 7-1-2010 at 11:26


Hum, I shall review it. I have notes here saying that Fe2O3 is not very good. Maybe it is a wrong notation. Thank you for advise, Picric-A.

Best regards, Dúlio.




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[*] posted on 7-1-2010 at 11:28


Quote: Originally posted by D S2 A  
Hum, I shall review it. I have notes here saying that Fe2O3 is not very good. Maybe it is a wrong notation. Thank you for advise, Picric-A.

Best regards, Dúlio.


Indeed Fe2O3 is a fairly bad catalyst for this but you said V2O5 is unavailable,
I said you were wrong becuase you said you have searched for an hour which is obviously wrong.
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[*] posted on 7-1-2010 at 11:34


I am searching for methods to produce SO3 and produce oleum. I know the procedure with V2O5 but I want to avoid it. I shall not have unlimited resourses and equipment to produce SO3. I spent most of time on esterifications, not on oleum and related...

Best regards, Dúlio.




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