Sciencemadness Discussion Board

Aspirin purification.

Veruth - 26-12-2006 at 11:03

I'm doing a small test in preparation for a picric acid synthesis I want to try, but I'm not quite sure if it came out right.
I dissolved 63 aspirin tablets each containing 325 mg ASA in about 250ml acetone. The resulting mixture was then filtered to remove the insoluble binders, fillers, etc. The resulting liquid was then placed on low heat (a scavenged coffee pot heating element) to speed up the evaporation. When all the solvent boiled off I was left with a white cake in the bottom of the container. It's not dry yet, but it has an odd vinegar smell to it. This makes me wonder if the heat was high enough to decompose the ASA or if there is some other reason for it. Or maybe it's got something to do with the acetone, most things I have read recommend ethyl or isopropyl alcohol.

pantone159 - 26-12-2006 at 11:15

If the aspirin was old, perhaps is was already decomposing, before you evaporated it?

Veruth - 26-12-2006 at 11:40

It shouldn't be too old, I bought it two days ago. I guess there is no way of knowing how long it's been on a shelf there though.
Also, I'm not sure if it's decomposing or not, it's just my guess.

Aqua_Fortis_100% - 26-12-2006 at 13:35

I'm also not sure about which the very old ASA affect the TNP manufacture ... because mine is old (3 years) and in any case apparently work when i made some TNP..
anyone can help me about this?

and about the solvent for extract the ASA i think which is better use Ethy Alcohol because it's cheap(almost always more than acetone ,isopropyl alcohol,etc),and more easy to find...
-----
procedure used many time ago:
first, put mine 500ml of EtOH in a plastic thin container and this in another plastic container (bigger than first ) filled with very hot water, and then adding the 125 crushed 500mg tablets of cheap brand of aspirin in EtOH, and then stired with a spoon.. then i filter the alcoholic solution through a coffee filter and put this solution in another similar container, but with many more surface to make it more easy and quick to evapore the EtOH... put this in same bigger container filled with hot water(hot water replaced constantly ,working as hotplate..).. ready!

(if you evapore too quick the EtOH, you got small shinny crystals, but if you evapore the solution to saturation point or little more, and then stop the heat and close the container and wait , you will see nice very BIG and almost perfect crystals of ASA ! :D )

haha in this new year's eve the noise of TNP and DDNP will be audible here.. :D

[sorry about my poor english..]

Sauron - 26-12-2006 at 13:48

Interpose a water bath and heat the bath to 50-80 C.

The acetone boils low and loves to evaporate.

This way you avoid any chance of decomposing your ASA.

Ordinary nitrations w/mixed acid generally give a lot of tar in picric acid preps. I seem to recall a very mild heterogenous nitration of phenol that was high yield and didn't give tars at all. It was in an Iranian journal maybe? Wasn't it on the Hive?

Aqua_Fortis_100% - 26-12-2006 at 16:27

thanks Sauron..
the acetone has a boil point lower than EtOH, so really maybe better... but actually here isn't great because the cost of Acetone is very expensive and is very hard to find (as some others solvents here ,it has controlated sales because is used for criminals to make drugs ..), I tried the dry calcium acetate pyrolisis for got mine acetone, but the yield is really poor,some mililiters.. so , for me the EtOH is the best..

about the nitration of ASA/phenol unfortunately i haven't nitric acid , phenol or a DECENT sulfuric acid (mine is a filtrated and strongly boiled battery acid) ..
mine nitration of ASA was very weird..
first i heat my conc H2SO4 in a simple glass container and add the ASA, slowly.. all dissolves while boil and no any colour has observed,but after 10 minutes or less, a white and volumous mass of crystals precipite in hot boling H2SO4!!! what's the substance? somewhat as "ASA sulphate" or phenol sulfate??? why the colour not becomes red and black? this is normal???

[[[[about the phenol method ,my very old Industrial chemistry book (publicated in 1960!), says which the "H2SO4 acts on phenol and transform them in a dissulfonated phenol:
<IMG SRC="C:\Documents and Settings\Carlos\Meus documentos\Minhas imagens\Pyroimages\dissulfonatedphenol.jpg">
which is poured in a mix formed by 4 parts HNO3 (at 28°Be) and 3,2 parts NaNO3 [the book does not especifit if pbw or pbv...].. so due the replacement of two SO3H by two NO2 and the introduction of another NO2 radical in position 6 ,making a Tri-Nitro-Phenol .."]]]]

well, after a little more wait on fire of burner, i retire the glass container and being to add my purified double nitrate (from fertilizer) or KNO3 extracted and purified from black powder... almost instantly, the H2SO4 becomes very dark-red, then after red and finally orange,always releasing a very poisonous red gas (NO2)... after the additions i set stand the container and fill another container with crushed ice and dump the cooled orange poisonous liquid in it.. yellow nice crystals appeared.. wait the ice melts, then i filtered the crude precipitate and dissolve them in minimal amount of hot water(aprox 15ml).. then the yellow solution was cooled to -10°C with a salt ice bath ad filtered again... sorry by no provide the exact weights because i have no accurate scales at the moment... (i Also saved the first solution from orange liquid + ice for catch more TNP later.. :cool: ) ... my TNP was dry in filter and stain all with a strong yellow colour..but i handle this ONLY with a glove to protect my skin...

[sorry about my poor english and by the poor format of scanned pick...]

[Editado em 27-12-2006 por Aqua_Fortis_100%]

Sauron - 26-12-2006 at 16:36

Two alternatives:

Recover your distilled acetone instead of just letting it evaporate to the air. A rotary evaporator would be most convenient.

If acetone is expensive in Brasil, can you get 2-propanol (isopropyl alcohol?) Often sold as rubbing alcohol at 70%

If you can get this (preferably anhydrous) you can easily oxidize it to the acetone. It can't proceed beyond the ketone stage (like aldehydes can.)

Veruth - 26-12-2006 at 17:26

The heating element I was using isn't hot enough to boil water, and the acetone was boiling, so I'd estimate the temperature to be between 50 and 100 degrees. Would that even be enough to decompose ASA? Since this is a test batch, I might try a few more times with other solvents since I've got most of the ones recommended.

pantone159 - 26-12-2006 at 18:08

Can you get 95% or so EtOH? A mixed solvent recrystallization by dissolving aspirin in hot EtOH, filtering, adding hot H2O until just cloudy, then a little more EtOH to clear, then cool eventually in the freezer will give nice ASA crystals, without needing to evaporate the solvent.

The same treatment with acetone might work too, I haven't tried it. (E.g. dissolve aspirin in hot acetone, filter, add just the right amount of hot water, then chill, hopefully filter nice crystals.)

Veruth - 26-12-2006 at 19:25

Well, I've got denatured. Think the methanol would be much of a problem? If not, I'll try that. If so, I might be able to get some without it but it would take me a little longer since I'm underage and everything.

[Edited on 27-12-2006 by Veruth]

pantone159 - 26-12-2006 at 21:08

Quote:
Originally posted by Veruth
Think the methanol would be much of a problem?


No.

Aqua_Fortis_100% - 26-12-2006 at 21:44

Quote:
originally posted by Sauron:
Two alternatives:

Recover your distilled acetone instead of just letting it evaporate to the air. A rotary evaporator would be most convenient.

If acetone is expensive in Brasil, can you get 2-propanol (isopropyl alcohol?) Often sold as rubbing alcohol at 70%

If you can get this (preferably anhydrous) you can easily oxidize it to the acetone. It can't proceed beyond the ketone stage (like aldehydes can.)


Thanks again! to distil the solvent can be very convenient.. this is a great idea..(here the acetone most easy to bought ,if you is a common person, is a nail polish remover..(50-60%) ) .. about the isopropyl alcool, it is common pure ,but still expensive, even the 70% grade..( usually 5 times more expensive than EtOH)...about the oxidation to ketone unfortunately i'm not have the right materials to make it with safe..

Quote:
originally posted by pantone159 :
Can you get 95% or so EtOH? A mixed solvent recrystallization by dissolving aspirin in hot EtOH, filtering, adding hot H2O until just cloudy, then a little more EtOH to clear, then cool eventually in the freezer will give nice ASA crystals, without needing to evaporate the solvent.

The same treatment with acetone might work too, I haven't tried it. (E.g. dissolve aspirin in hot acetone, filter, add just the right amount of hot water, then chill, hopefully filter nice crystals.)


is another interesting idea, since (you just says) "without needing to evaporate the solvent"..
but can you tell me if this method has less yield than if evaporate all solvent?? thanks.

i'm really interested in Sauron's idea to recover the solvent by destill... but the safe for destill EtOH or acetone is mine major problem... In my yard there are TONS of charcoal and wood,so think if used for provide heat for destill and using more elabored homemade AND SUFFICIENTLY SAFE apparatus(with safe hotplate, right exit for the EtOH vapours, control of the flame, etc) , will can make the EtOH ,acetone or another common solvent becomes very cheap! (though it's become more and more impure each time which you recycle the solvent)...
what you think about this?
Quote:
originally posted by Veruth:
Well, I've got denatured. Think the methanol would be much of a problem? If not, I'll try that. If so, I might be able to get some without it but it would take me a little longer since I'm underage and everything.

[Edited on 27-12-2006 by Veruth]

well , if methanol is better than other solvents to dissolve ASA, i'm not sure,but i advise if you not have the sufficient protection against this nasty chemical, you must abort the ASA separation because the methanol vapour is a very bad thing to your eyes,brain,body,life... i NEVER worked with methanol by 3 reasons:
1) I never find this here (in common places,but in a chemical supplier i see)..
2)even if get one liter of this , i will NEVER use them, because great toxity and potential to fuck with live things ...(afraid specially about the methanol vapour.. nasty thing! :mad: )
3) even handling Methanol with care,and no instant damage observed this will can affect you(maybe permanently) later in life...


[sorry about my poor english.. i try to improve my grammar...]

[Editado em 27-12-2006 por Aqua_Fortis_100%]

pantone159 - 26-12-2006 at 22:03

Quote:
Originally posted by Aqua_Fortis_100%
is another interesting idea, since (you just says) "without needing to evaporate the solvent"..
but can you tell me if this method has less yield than if evaporate all solvent?? thanks.


Yes, but the product should be more pure. For me, in my dabblings, aspirin is so cheap that I hardly care.

Aqua_Fortis_100% - 26-12-2006 at 22:51

Oh, thanks again Pantone !
then next time when to buy some aspirin i will realize this procedure..
but i must also buy the lab grade 98% H2SO4 and if possible also HNO3 for more little funs! :D

---------------------------

some doubts:
the sodium or potassium bisulphate formed when my nitrates reacts with H2SO4 does not affect significantly the properties of TNP??? why the reason which the TNP not form picrates with these salts while it's made???
thanks all...

[sorry by my poor english, and any stupid question]

Nicodem - 27-12-2006 at 12:31

Quote:
Originally posted by Veruth
It's not dry yet, but it has an odd vinegar smell to it. This makes me wonder if the heat was high enough to decompose the ASA or if there is some other reason for it.

I'm wandering why would it matter if aspiring partially hydrolyzed during the isolation if it is going to be nitrated to picric acid anyway? Both aspirin (acetyl salicylic acid) and salicylic acid get nitrated to the same product anyway.
You can't avoid partial hydrolysis if you boil off acetone unless you use every solvent dry. Rather vacuum strip the solvent or use a dish with large area for evaporation at room temperature. If pure aspirin is needed then just recrystallize it like Pantone suggested.