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tom haggen
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acetylsalicylic acid
The other night I took some powdered aspirin tablets, and dumped them into some 99% rubbing alcohol. Everything was going smoothly but it was taking
for ever for things to filter. Anyway once I got past that, I took the remaining solution and started distilling off the alcohol, expecting the
acetylsalicylic acid to precipitate out. Instead it boiled down in to a most disgusting light brownish , tree sap like goo. Does anyone know what
happened?
[Edited on 8-2-2004 by tom haggen]
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vulture
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Sounds like decarboxylation to me....
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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tom haggen
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Should I use less heat to avoid this? any advice is greatly appreciated.
[Edited on 9-2-2004 by tom haggen]
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JDP
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Was the rubbing alcohol you used Isopropyl? If so, I'm not really shure what happend, but I have heard of people haveing problems with
recristalizeing from isopropinol, saying it yielded lots of acidic acid vbapors and sutch.
~JDP
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guaguanco
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acetylsalicylic Acid is an easily hydrolysed ester, so you're going to want to protect it from water if you're going to be boiling it. I
would expect that you've ended up with a mixture of salicylic acid, acetylsalicylic acid, acetic acid, isopropanol, perhaps traces of isopropyl
acetate. A fine mess.
You're best bet is recrystallizing it from something like ether or methylene chloride
[Edited on 9-2-2004 by guaguanco]
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Darkfire
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Ive never had a problem just tossing in asprin myself.
\"I love being alive and will be the best man I possibly can. I will take love wherever I find it and offer it to everyone who will take it. I
will seek knowledge from those wiser and teach those who wish to learn from me.\" Duane Allman
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JDP
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I always just pureify my ASA with acetone, since it's the cheapest solivent I have access to, about $10 a gallon. after it's dissolved I
just put it though a filter and dry it in the open air.
~JDP
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tom haggen
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Are you sure that the starch and other parts of the coating are not miscible in acetone?
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Mumbles
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The filler for the most part is not soluble. The filler in mine consists of microcrystaline cellulose, starch and Magnesium Stearate. None of which
are soluble. I think if the filler consists of Carnauba wax, you may get a small amout of that in the final product.
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tom haggen
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So using acetone as a solvent will eliminate all possiblities of decarboxylation? That stuff is so nasty I could barely scrub it out of my beautiful
glass beaker. And I scratched the shit out of my glass trying to clean it.
[Edited on 10-2-2004 by tom haggen]
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guaguanco
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| Quote: | Originally posted by tom haggen
So using acetone as a solvent will eliminate all possiblities of decarboxylation?
[Edited on 10-2-2004 by tom haggen] |
salicylic acid is quite stable. You're not going to decarboxylate it at the temperature of boiling acetone.
If you recrystallize it from a reasonably dry aprotic solvent like acetone, you should be able to prevent hydrolysis.
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tom haggen
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Thank you everyone for your help. I guess I will try to recrystallize actelysalicylic acid with acetone at the lowest temp. possible.
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Mendeleev
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I had a question about the filtering. I also have the problem of taking to long to filter things. The precipitate accumulates at the bottom of the
filter and does not allow any more water to pass, so it takes a long time. Does anybody have any remedy for this besides using a separate filter for
each gram of precipitate? How the hell to they do it industrially? I'm sure World War II would not have lasted a week if it took them this long
to get 100 grams of precipated HE or anything else.
Trogdor was a man. A dragon man. Or maybe just a dragon. . .
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tom haggen
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I have found that the oxidisers I have worked with filter with ease. When my solution is piping hot, the filtrate flows like a water fall thru the
filter paper, and the contaminates collected in the filter are discarded. Filtering Acetone Peroxide moves along quick enough, but I usually have like
2 containers with filters, and switch back and forth. The other night when I was filtering acetylsalicylic acid, I had 4 filtering containers going,
and things were filtering at a snails pace. I just about went postal when my filtrate decarboxylized, and I waited all that time for filtering.
[Edited on 15-2-2004 by tom haggen]
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Hermes_Trismegistus
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| Quote: | Originally posted by Mendeleev
I had a question about the filtering. I also have the problem of taking to long to filter things. The precipitate accumulates at the bottom of the
filter and does not allow any more water to pass, so it takes a long time. Does anybody have any remedy for this besides using a separate filter for
each gram of precipitate? How the hell to they do it industrially? I'm sure World War II would not have lasted a week if it took them this long
to get 100 grams of precipated HE or anything else. |
Flute your filter paper
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Mendeleev
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What mean this "flute"?
Trogdor was a man. A dragon man. Or maybe just a dragon. . .
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Hermes_Trismegistus
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Please note, this is a difficult thing to describe in words.....but I'll try.
**(fold twice if your paper is smaller 6cm diameter, thrice if larger than 8cm diameter)**
fold your filter paper in half, twice/thrice, unfold without rebending out the creases
fold in half again, twice/thrice, only this time with the new creases halfway in between the old creases, and in the opposite direction,unfold without
rebending out the creases.
(advanced) fold two opposite creases in so that a two opposing tunnels are formed
***note
this is a bit of origami that will serve you well, but if you have more time than money pre-folded filter papers are available.
However, only real filter paper is stiff enough to stand up to the mass of the filtrate\solvent without deforming.
buy real filter paper, cheap....efficient and light enough to mailorder at little expense.
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Mumbles
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You could always use vacuum filtration. A filter flask, aspirator, and buchner funnel will put you back maybe $30.
I don't know how it's done in industry, but I'd think a vacuum would be kind of expensive to use like that.
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Hermes_Trismegistus
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still need to flute your paper.
Especially with vacuum, or you'll suck a wad of paper/filtrate right into your funnel.
In industry the simplest system they use is a very fine stainless steel mesh "bowl" the wash goes into the bowl and centrifugal force
spins the solvent out the sides and down the sides of the vessel. The filtrate is spun out and up the sides of the mesh "bowl" to be
collected at the top rim.
it just gets more complicated from there.
If you do alot of filtration, you may wish to invest in a mesh yourself. You can get some of the mesh from those "filterless" coffee
machines. (order a replacement "filter" from customer service)
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Hermes_Trismegistus
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quote:
--------------------------------------------------------------------------------
Originally posted by Mumbles
. A filter flask, aspirator, and buchner funnel will put you back maybe $30.
--------------------------------------------------------------------------------
Wow! those are awesome prices you're getting.
I'd end up paying at least 70 dollars for the same setup and even with the one liter filter flask I'd still be filtering smaller amounts at
a reasonably slow pace.
using your handy shop vac for vacuum filtration isn't a big deal, you just need to set an approprate duty cylcle to avoid overheating and using a
jar(or five gallon glass carboy with humumgo automotive funnel) with two holes punched in the lid(or a two hole stopper from a homebrewing supply
store) to collect the solvent. Then attatch one of the holes to a hose and the other to your funnel.
Hold the end of the hose at the intake of your vacuum, The amount of a seal you regulate with your hand will determine the amount of suction. (and how
fast the vacuum motor overheats)
The aspirators are more important in applications where a cheap(I'd pay about forty dollars canadian plus shipping plus duty) constant and
consistent vacuum is needed. (like vacuum distillation)
***note, you may need to have an intermediate bubbler or filter between the filter and the vacuum for safety.
Depends on your solvent, I wouldn't (personally) bother with acetone, I'd just do it outside. I would definitely use it if I was using
ether.
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Mumbles
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| Quote: | Originally posted by Hermes_Trismegistus
Still need to flute your paper
Especially with vacuum, or you'll suck a wad of paper/filtrate right into your funnel.
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A buchner funnel is different than a normal funnel. Its like a cylindrical bowl with holes in the bottom. Then it tapers off and is connected to the
flask by stopper. They do have these metal screens you place under the filter paper to improve flow. This acts like fluting to an extent.
http://campus.murraystate.edu/academic/faculty/Beth.Brubaker... A picture
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Mendeleev
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http://www.service-filtration.com/Admiral-Filtration-Systems... Does anybody think something like this will work? Are these the kind that work
using the fine steel mesh centrifuge bowls? What really attracts me is that is says they are acid proof. As far as the "real" filter paper
goes, it should be sold at any normal science supplier right?
Trogdor was a man. A dragon man. Or maybe just a dragon. . .
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tom haggen
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So if I try to recrystalize acetylsalicylic acid with say 70% isopropyl alcohol I will risk hydrolysis because of the 30% H2O content. Is hydrolysis
what causes acetylsalicylic acid to get so sticky sometimes? Also, if I recrystalize acetylsalicylic acid with 70% isopropyl alcohol, can I avoid
decarboxylation if I evaportate the alcohol off over a water bath below 85 degrees Celcius? Guess I will be finding out soon since i'm running
this exact experiment right now.
[Edited on 20-3-2004 by tom haggen]
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Esplosivo
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The decarboxylation of acetylsalicylic acid occurs at a temperature of around 140 deg Celcius, therefore evaporating the alcohol using a water-bath
will prevent temperatures going in excess of 100 deg Celcius.
I cannot understand the effect being spoken about the ester being hydrolysed by the water. As far as I know hydrolysation of Acetylsalicylic acid
occurs in alkaline conditions and not in 'neutral' water.
Anyway, if this is true, the isopropyl acohol can first be removed by maintaining a constant temperature of around 86 deg Celcius in the water bath.
If the conc. of isopropyl alcohol is 70% then as an approximation one can say that when nearly 3/4 ths of the solution evaporated the remaining is
some alcohol, water and the ester. The ester, being slightly soluble in water, could then be crystrallized out of solution by cooling the mixture in
an ice-salt mixture or something of the sort. This can be carried out if one assumes that the ester is not hydrolysed (as mentioned) at temperatures
lower than 90 deg celcius.
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tom haggen
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Sorry for my lack of knowledge, but if the acetylsalicylic acid becomes hydrolysed by the water will this form a new compound? Anyway, I heated the
solution over a water bath @85C for a couple of hours. Went to bed and the acetylsalicylic acid was still disolved in the remaining solution. when I
woke up and checked it, to my satisfaction much of the acetylsalicylic acid precipitated out. No decarboxylation or anything. I think I will just let
the rest of it dry out in the sun see as how it's going to be warm today. I just curious if the any acetylsalicylic acid was hydrolysed by the
30% water content of my isopropyl alcohol would it have formed a new compound?
[Edited on 20-3-2004 by tom haggen]
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