Sciencemadness Discussion Board

acetylsalicylic acid

tom haggen - 8-2-2004 at 11:03

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]

vulture - 8-2-2004 at 11:06

Sounds like decarboxylation to me....

tom haggen - 8-2-2004 at 15:40

Should I use less heat to avoid this? any advice is greatly appreciated.


[Edited on 9-2-2004 by tom haggen]

JDP - 8-2-2004 at 20:25

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.

guaguanco - 8-2-2004 at 22:15

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]

Darkfire - 8-2-2004 at 22:28

Ive never had a problem just tossing in asprin myself.

JDP - 8-2-2004 at 22:38

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.

tom haggen - 9-2-2004 at 12:21

Are you sure that the starch and other parts of the coating are not miscible in acetone?

Mumbles - 9-2-2004 at 15:56

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.

tom haggen - 9-2-2004 at 19:30

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]

guaguanco - 9-2-2004 at 20:15

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.

tom haggen - 9-2-2004 at 21:08

Thank you everyone for your help. I guess I will try to recrystallize actelysalicylic acid with acetone at the lowest temp. possible.

Mendeleev - 14-2-2004 at 20:03

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.

tom haggen - 14-2-2004 at 21:11

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]

Hermes_Trismegistus - 14-2-2004 at 21:30

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:)

Mendeleev - 14-2-2004 at 21:45

What mean this "flute"?

Hermes_Trismegistus - 14-2-2004 at 22:42

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.

Mumbles - 15-2-2004 at 10:32

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.

still need to flute your paper.

Hermes_Trismegistus - 15-2-2004 at 14:35

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)

;)

Hermes_Trismegistus - 15-2-2004 at 15:05

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.

Mumbles - 15-2-2004 at 19:49

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.


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

Mendeleev - 16-2-2004 at 09:47

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?

tom haggen - 19-3-2004 at 22:53

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]

Esplosivo - 20-3-2004 at 07:14

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.

tom haggen - 20-3-2004 at 09:12

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]

tom haggen - 20-3-2004 at 18:33

Well today I evaporated off the remaining isopropyl which was mixed with acetylsalicylic acid. I got some pretty awsome crystal formations. what do you guys think?

IMGA0145.JPG - 109kB

Geomancer - 22-3-2004 at 18:57

Yesterday and today, I recrystalised two batches of asprin, one of 13g and one of 68.25g. No undue problems were encountered. I will give the procedure for the second batch.

The tablets were crushed until they were mostly powder, then added to 100mL of boiling ethanol. The ethanol was again heated to boiling, and filtered through two coffee filters with a small amount of diatomaceous earth deposited (my earlier attempt demonstrated that some stuff gets through the filters). Even though the assembly was being warmed, some crystaliztion occurred. I washed the filter cake with an aditional 25mL or so of hot ethanol, though it appears some crystals were still left. Also, some stuff got through the filter even with the DE. I attempted to remove this by sedimentation and decantation, but this was only partly successfull.
The filtrate is relatively unsaturated, as filtering more saturated solutions proved problematic (think stalagtites, etc.). Crystalization begins only relatively close to room temperature. After the product had cooled to room temperature( with considerable crystal growth), I added 100mL or so of cool water. Precipitation was almost instantaneous, with the solution quickly turning opaque and then into slush. The entire jar was involved, so I added about 20mL more water to make sure I had gotten most of it, and stuck the thing in the freezer. After the solution had cooled, I broke up the slush and filtered through a single coffee filter. I washed the filter cake with several portions of water (about 100-200mL total). The product is in the form of needle-like white plates.

Aspirin was from Rite-Aid, lightly coated, 325mg tablets.
Ethanol was from the hardware store, claims to be denatured with methanol.

Sir Dudalot - 23-3-2004 at 14:14

I've always just dissolved my asprin in acetone then filtered and left the acetone out for a day or so to evaporate. This was during the summer when it was warmer though (aournd 20*C at night). I never had any problems with slow filtering. I bought my asprin at a local drugstore and my acetone at my local hardware store. Nothing special. No heating involved.

Geomancer - 23-3-2004 at 19:47

I chose to recrystalize rather than simply extracting. No doubt this is just another sign of my latent eletist tendencies.

Aspirin hydrolysis

roger2003 - 28-3-2004 at 03:01

For details see:


http://files.irt.drexel.edu/courseweb/ScienceInMotion/newman...

tom haggen - 28-3-2004 at 08:52

My Acetylsalicylic acid was also recrystallized. I think I have been using the term extraction incorrectly lately. Forgive me for my misuse of terminology.

[Edited on 28-3-2004 by tom haggen]

Geomancer - 28-3-2004 at 15:55

roger2003: Sweet. Interesting that they use acid hydrolysis. I've been using basic hydrolysis.

The pH-Rate Dependence of the Hydrolysis of Aspirin

roger2003 - 29-3-2004 at 03:06

details:

http://www.md.ucl.ac.be/pharma/tpao/tpintegres/Cinetique_chi...

Geomancer - 30-3-2004 at 18:34

Here's somthing interesting. A few days ago, I dissolved a bunch of recrystalized ASA in excess base (Red Devil Lye in water). The starting material had a little phenol red added to help see what was going on. With the addition of enough base, the solution turned reddish, just as it is supposed to. Today (12:00) I came back to the (hopefully hydrolysed) solution. I added HCl to precipitate the product. The solution quickly turned yellow, even before most of the precipitation was complete. I continued adding acid until it was clear that I had got everything I was going to get. A smallish quantity of gas was evolved (this happened the previous time too. I hope it doesn't indicate decarboxylation), and there was a definite acetic odor (as expected). Around 8:00 I returned to filter off the product. The solution was green. What's up with that?

Esplosivo - 30-3-2004 at 21:24

The acetic odour given off shows that your ASA has been broken down to salicylic acid (also good for making picric acid).

tom haggen - 31-3-2004 at 16:04

Last time I recrystallized asa it reeked of an acetic odor. I used 70/30 isopropyl alcohol. It didn't take any over heating to accomplish this

[Edited on 1-4-2004 by tom haggen]

Mumbles - 1-4-2004 at 10:06

Ok Explosivo, perhaps you should read his post a bit more carefully. He said the acetic odor was expected. I take this to mean that he knows of the simple concept of hydrolysation. There is no need to pound that into the ground.

As for the green color. My best guess would be that some sort of Chlorosalicylic acid formed perhaps. Maybe the HCl decomposed and there is not Cl in the liquid. Perhaps the shade of green could help a bit more.

Esplosivo - 1-4-2004 at 10:26

Sorry, my bad. I missed the "as expected" part.

Well, the solution turned green. What was the intensity of the green colour. A pale faint green colouration would mean that there is Cl2 present, which I doubt since it would have reacted with the salicylic acid right? Could have been any impurity which formed a complex, such as copper imuprities forming complexes because of the acetic acid and the chloride ions?

Geomancer - 1-4-2004 at 17:04

I'm begining to think the situation isn't half as interesting as I thought it was. The solution was green, alright, a watery emerald green. But I now think it was contamination, specificly I think the acid solution was corrosive to the stainless steel spoon I had left in it. When I removed the spoon, I noticed a small amount of pitting and blackish residue as well as a less shiny surface. I dont know much about salycilate complexes, but I do know iron forms a purple one, so the contaminant isn't iron, or at least not ferric iron. Assuming that the steel is some combination of Fe, Cr, Ni and Cu, this would mean it's Cr<sup>3+</sup>, no?

thunderfvck - 1-4-2004 at 22:53

Cu+2 is green.

Geomancer - 2-4-2004 at 15:03

Quote:
Originally posted by thunderfvck
Cu+2 is green.


Yes, but copper would oxidize any exposed iron.

Geomancer - 5-4-2004 at 19:52

Yesterday I came back to my crude salicylic acid, which I had left out to dry after an incomplete and slow filtration (the white sludge liked the water more than gravity did). It was still damp, and the galvanized steel mesh I had been supporting it on had corroded badly (duh). I decided not to waste more time on drying, and dissolved it in the minimum amount of boiling ethanol. The solution immediately turned purple. Whether this was due to iron from my spoon or from the mesh I don't know. Upon filtration, losses due to premature crystalization were small and manageable, unlike with my attempts to recrystallize ASA from saturated solution. Crystals apeared to have difficulty nucleating, with initial growth confined to a large, flat, single crystal on the surface and some growth on the glass around the edges of the solution. Later crystals grew thoughout the solution, and, apparently, the growth action forced the upper crust a few mm above the liquid level. After it had reached room temperature, I cooled it in the freezer, and then slowly added an equalish volume of boiling water. I niether observed any sudden crystal formation nor any gross dissolution of extant crystals. I then cooled and froze to get a few more crystals. I filtered and washed with several portions of ice water. The final portion of wash water had only a barely detectable lilac tinge. I added a small portion of rust from my ex steel mesh to the final wash water. No immediate color formation was visable. The crystals are in the form of white needles, with a coarse texture, that drain liquid well. This is different from my earlier sample, which had a texture vaguely reminiscent of cotton candy. This may be due to different techniques, or to one (or both) of the samples being contaminated (probably with ASA). For what it's worth, I think that recrystallizing from water would be a better choice, next time.

thunderfvck - 5-4-2004 at 21:06

Hey, wait a minute...Cu +2 is not green...It's blue!

I don't know what I was thinking. Must have been those homosexual tendencies, once again...

Off topic to THIS subject but I don't want to open a whole new thread...I have a copper penny in some HCl, the solution is green. Cu+2 is in there, yes? CuCl2. Why is it green?

So it wasn't the homosexuality afterall...

The_Davster - 6-4-2004 at 15:38

I believe that copper(II) is green when it it is with a halogen anion. Otherwise it is blue.

Geomancer - 6-4-2004 at 16:56

Homosexuality causes one to see colors wrong? Copper ions change color depending on the ligands that coordinate with them. Chloride is capable of displacing water from the hexaaqua complex (blueish) to form the tetrachlorobiaqua complex (green) (I may be getting the nomenclature screwed up here). Bromide and ammonia also give distinctive colors; go to the "Complex Ions of Coppper" thread for more details.

I came back to my final wash water+rust from the previous post this morning. Purple! Apparently it takes some time for the rust to dissolve sufficiently. Either that or the "homosexual agenda" is alive and well.