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All 18 posts   Subject: Improved recrystallization   Please login to post   Down

 
    Prepuce
(Hive Bee)
11-03-04 06:46
No 539384
User Picture 
      Improved recrystallization     

SWIP wouldn't presume to teach anything to the real chemists in this forum, and maybe not to some of the more experienced bees either. But he ran into an improvement on the procedure he believes most bees use, and while the changes are very small, they made a huge difference. SWIP bets that you'll be pleasantly surprised at the results if you try it, but only if you carefully follow the procedure.

You will need:
  1-2 ehrlenmeyer flasks or ghetto equivalent
  2 small beakers, ~50 ml depending on the size of your sample.
  Denatured alcohol (the kind with methanol as denaturant works well)
  Acetone
  Eye dropper

Gently heat a small beaker of denatured alcohol. (Not on a flame, of course, and don't forget to aim a fan to blow the fumes away from any source of ignition.) Put the substance you want to recrystallize in a small ehrlenmeyer flask or ghetto equivalent, and add hot denat drop-by-drop until the sample disolves and cloudiness in the solution just clears.

If the solution has any suspended particles, add additional hot solvent to prevent crystals from forming, then hot-filter the solution through a moderately compacted Charmin plug. Don't use vacuum or crystals may form and get stuck in the filter. Rinse the original beaker 2-3 times with a little hot denat and pour it through the filter. Finally, pour some denat directly on the filter to minimize losses. Examine the solution, and if there is still any trace of suspended particles, repeat filtering but use a more tightly compacted Charmin plug.

Put the clear solution on heat and evap until solids start to appear. Blow air from a hair dryer across the surface if you want to speed things along. Then add hot denat drop-by-drop until all has redisolved and the cloudiness in the solution has just disappeared.

Poor a small amount of acetone into another small beaker. With an eyedropper, add the acetone drop-by-drop to the denat solution until it just turns cloudy. You'll have to look close because it's not really easy to see. Now add just enough hot denat--maybe a drop or two--to make the cloudiness disappear.

Let the sample cool, cover, then place in the coldest spot you can find in the freezer. Be prepared for a surprise when you return in about a half hour.

decant the mother liquor off of the crystals, then rinse the crystals with ice cold acetone. Don't throw away the remaining mother liquor, as it still contains a little of your sample. When you're ready you can evaporate/recrystallize this to recover a little more product.

Like SWIP said, this isn't a departure from the normal procedure, but there are some indicators that help to get repeateable results. SWIP has been dreaming about recrystallizing for several years, and thought he had become somewhat proficient. The first time he dreamt about trying these changes, though, he had to do it over three times before he got it right.

When he finally finished the process and thought the flask was cool enough to put in the freezer, he was disappointed to see no crystals beginning to form. Not even anything on the surface. He stuck it in the freezer anyway, thinking he might get something to fall out anyway. He checked a half hour later to see if it looked promising, and was astonished to see that the flask was crammed with large crystals! They filled the flask up to the line of the solvent, and many were at least 1/4 inch long and 1/8+ inch wide. After less than 1/2 hour! Imagine what it will look like after sitting overnight, or after a second recrystallization. One big diamond maybe?

PP
 
 
 
 
    Jacked
(Ancient Alchemist Delux)
11-03-04 08:42
No 539400
      reply     

All the freezer is doing is making the crystals form way to fast to purify. Thats why the majority will purify there product by slow recrystallization. And whats new about duel solvent recrystallizing that you are doing? Other than rushing the formation of the crystals..

Tighten Up!  (UH)
 
 
 
 
    Amnesia
(Newbee)
11-03-04 12:03
No 539415
      Yeah i cant see how this is any different to...     

Yeah i cant see how this is any different to the dual re-x procedures stated here million times over.
Can you point it out prepuce and how it makes it better than the procedures already stated, because all i can see is rushing of the crystal formations which gives a worse product.
 
 
 
 
    WizardX
(Wizard Master)
11-04-04 02:56
No 539575
User Picture 
      Activated Charcoal     

Some recrystallisation methods use Activated Charcoal for extra purification.
 
 
 
 
    Prepuce
(Hive Bee)
11-04-04 05:25
No 539596
User Picture 
      What's different     

Jacked, what's new about this is definitely subtle, and I'm sure there are some to who there is nothing new about it. SWIP is assuming that the way he learned to do recrystallization, strictly from reading posts to the Hive, is similar to what others are doing. Namely, disolve the sample in a little solvent, heat until it gets to that "just right" point, then flood it with acetone. If any crystals fall right out, add just a bit more solvent. Nothing wrong with that procedure at all. SWIP has been using it for several years.

The only trouble he's had has been getting the solution to just the right stage every time. Even with all the practice he's had, he still misses from time to time, and some results are better than others.


What he likes about this procedure is that there is a signal  to say when it's had enough of the solvent, and another to say when it's had enough acetone. SWIP has been able to produce consistent results for the first time by following these steps. But in addition, you end up with less total liquid and SWIP thinks that's significant in the formation fo the crystals. While it's surely obvious to many, but the filtering technique as it's applied is very efficient and all but lossless.

SWIP has never before suceeded in growing such large crystals on the first recrystallization, even when left overnight. He couldn't believe it when they grew in about 1/2 hour, but he agrees with you--that's rushing things. If crystals like this form in a half hour, what will they look like after growing all night?

To summarize, the technique offered SWIP consistent and better results than he's ever previously acheived. Realistically, he never expected to teach you anything about growing crystals!

PP
 
 
 
 
    Prepuce
(Hive Bee)
11-04-04 05:29
No 539598
User Picture 
      Been meaning to look into charcoal     

WX, SWIP has been meaning to investigate the use of charcoal to clarify a solution before recrystallization. It is his understanding that charcoal is especially effective in removing an off-color. He's been worndering if carbon, such as that sold for acquarium filters, could be finely ground and used in place of charcoal. For the ghetto chemist it looks like it's easier to pick up good quality carbon than charcoal.

PP
 
 
 
 
    biotechdude
(Hive Bee)
11-04-04 07:51
No 539614
User Picture 
      good, but take care     

Some recrystallisation methods use Activated Charcoal for extra purification

Actived Charcoal (carbon) is readily available (aquarium shops, home brew barns..).  Get the best quality.

Word of caution.  Activated carbon can absorb some of the end product.  The main factors are time, ammount of ActC used (active sites), and end product/impurity ratios. 

Also keep in mind that the ActC will need to be filtered/removed.  The mechanical loss (esp is conc. solutions) can be a yield killer. 

Swib has used it to clarify fb-ephedrine steam distillate from fine organic matter.  Worked ok.  Haven't had a need to do it on the end product; so can't vouch for that.
 
 
 
 
    Prepuce
(Hive Bee)
11-05-04 05:41
No 539807
User Picture 
      use of activated charcoal     

Bio, SWIP thinks that if he were going to use activated charcoal, he would first dilute the liquid as if he were going to filter it, then once finished it could easily be re-concentrated. That should hold the losses down to minimum.

From what he has read, it should only take a tiny bit to do the job, but he's also read that it can be very difficult to remove. There is another material that is sometimes added to help take it out of the solution, but SWIP can't find the name of it at the moment.

It would be interesting to find out if AC might remove discoloration of, say, the piss yellow variety. SWIP has no idea what the mechanism of action is, but doesn't think he'll be holding his breath on that one.

PP
 
 
 
 
    Jacked
(Ancient Alchemist Delux)
11-05-04 08:50
No 539823
      what kind of troubles     

What kind of troubles have you had? A highly diluted solution of meth and alcohol will eventually produce crystals when the alcohol has been evaporated to a point were the solution is supersaturated and cant hold the shit.. So actually producing a crystal is going to be hard not to if let sit long enough.. Your post is articulate in the method and description and that in itself is a good thing that can be easily followed.. It still is referred to as a duel solvent recrystallizing.. Try letting it do its own thing, Wrap saran wrap over the top of your beaker and sit it some place were it will be undisturbed for a few days. Even with the saran wrap it will evaporate just at a slower rate. Check it every 12 hours but do not disturb it. You don't want it to evaporate to dryness so keep an eye on it. Save that mother liquid for the next recrystallizing. Even walking heavy around it can agitate it so be sneaky.. You wont be disappointed.

Tighten Up!  (UH)
 
 
 
 
    dasedbee
(Stranger)
11-05-04 22:00
No 539906
User Picture 
      Here in the ghetto     

we found the need to filter some pesky solids from a solution. Since we found ourselves "financially embarrassed" the vacume filtration setup was ruled out. The aparatus as illistrated makes use of the ceramic fuel filter used in vehicles with a carb. To house this a see-thru fuel filter was "carefully opened" using a hacksawwink, the paper element was removed, and the ceramic filter was insterted. To seat the filter automotive silicone was used to act as a large "O" ring to make the solution pass thru the filter instead of around it. The housing was then resealed with the silicone. Since this is a positive pressure filtration device, a squeeze bottle (like used in resturaunts for ketchup) was filled with the solution to be filtered. This device will not absorb liqiuds in this configuration. If a high flow (low resistance) configuration is desired, use the fuel filter with the original paper element. The disadvantage is the paper element will absorb some of the solution. A sand filter can be fabricated by the same method with the addition of a fine screen (like the reusable coffee filters) held in place by silicone to trap the sand in the filter.(for sand filtering the ceramic filter is ommitted) Vary the resistance by the amount of sand in the see-thru filter. Not real pretty, but it works.
ghetto_super_filter.jpg

Db
 
 
 
 
    WizardX
(Wizard Master)
11-06-04 05:48
No 539989
User Picture 
      Recrystallization
(Rated as: excellent)
    

Online Laboratory Tutorials http://wulfenite.fandm.edu/labtech/labtech.htm

Recrystallization  http://wulfenite.fandm.edu/labtech/recryst.htm

Recrystallization works only when the proper solvent is used. The solute must be relatively insoluble in the solvent at room temperature but much more soluble in the solvent at higher temperature. At the same time, impurities that are present must either be soluble in the solvent at room temperature or insoluble in the solvent at a high temperature.


Selecting a solvent http://wulfenite.fandm.edu/labtech/solvent.htm

Single solvent method  http://www.chem.ualberta.ca/~orglabs/recrystallization/theory/theory2_01.html

Two solvent method http://www.chem.ualberta.ca/~orglabs/recrystallization/theory/theory3_01.html


Melting Point Test. http://wulfenite.fandm.edu/labtech/melting.htm


What if crystals don't form? http://wulfenite.fandm.edu/labtech/crystals.htm

Another potential problem in recrystallization is that the solute sometimes comes out of solution in the form of an impure oil instead of forming purified crystals. This usually happens when the boiling point of the solvent is higher than the melting point of the compound, but this is not the only scenario in which this problem presents itself. If this begins to happen, cooling the solution will not stimulate crystallization, it will make the problem worse. If an oil begins to form, heat the solution until the oil portion dissolves and let the whole solution cool. As the oil begins to form again, stir the solution vigorously to break up the oil. The tiny beads of oil that result from this shaking may act as the nuclei for new crystal formation
 
 
 
 
    Prepuce
(Hive Bee)
11-06-04 06:49
No 539993
User Picture 
      No troubles, really     

Jacked,

SWIP hasn't really had trouble, just inconsistent results. Stopping the evaporation too late and getting a beaker full of instant tiny crystals the moment the acetone hits it. Or worse, stopping the evap too soon and having no crystals fall out because the solution wasn't supersaturated. These are not what SWIP would call problems. Not at all.

SWIP isn't sure but he thinks he learned his technique from one of SWIJ's posts a long time ago. He has always used a peice of plastic wrap, but he always places the beaker inside a freezer and normally lets it sit there for at least 12 hours. He's learned to grown nice crystals that way. No trouble. If he's in a hurry SWIP may steal a few crystals from the first round.

What he likes about the procedure he posted is, (in addition to the repeateablity of the steps), simply: big, high quality crystals quickly. Yes, they would be even better if not produced so fast. But using his old method, it would take SWIP two 12 hour recrystallizations to get to the point the new method takes him in 1/2 hour.

Certainly no dispute with any of the old rules, however.

PP
 
 
 
 
    Prepuce
(Hive Bee)
11-06-04 07:02
No 539994
User Picture 
      Getting rid of the oil     

WX,

Thanks for this post. A method for avoiding/getting rid of the oil is a subject that SWIP has not previosly seen addressed.

Now this is veerign a bit from the topic, but could a similar technique be applied to recover I2 from solution with a non-polar solvent? SWIP thinks that throwing the baby out with the bath water is the major problem with yeilds in reclaiming I2 post-reaction.

The only time SWIP has come close to achieving this goal was when he mixed some IPA with a beaker full of I2 in solution with xylene. As he had hoped, the I2 seemed to prefer the IPA, but when he added additional water, followed by a few ml of H2SO4, then sodium hypochlorite, he didn't get the crystals he had hoped for. Instead he got what appeared to be melted I2, which of course can't happen. It was an oily liquid with no noticable smell, but the fumes burned the eyes so badly it was impossible to work with. Even handling it long enough to get rid of it was a challenge. SWIP had a similar adventure when he tried to use acetone. He has even seen I2 left over from a reaction emerge this way, perhaps in solution with polysorbate 80. Do you think it's a lost cause?

PP
 
 
 
 
    Jacked
(Ancient Alchemist Delux)
11-06-04 16:30
No 540038
      reply     

Just so you understand that the method you have posted is nothing new at all. It has been covered many times over... And a fast grown crystal is more than likely to have trapped impurity's with in its lattes. IMHO it would be defeating the whole propose of recrystallizing.. Read the links WizardX posted. There full of good info and will back what I'm saying.
 As fas as the past problems listed, If for some reason your solution isn't supersaturated when you thought it was all you haft to do is heat it up again and evap a little more alcohol.. Tiny crystal in the filter? They should never hit the filter. Add a little more alcohol and heat to redissolve the premature crystals then filter.. Inconsistent results is because of inconsistent parameters in your methods and the simple fixes that can be done as the problem shows itself. It would be hard not to produce a crystal of some type as the mother liquid slowly evaporates.. Recrystallizing is one of the simplest possible process that people with little or no chem backgrounds at all can learn to do and with consistent outcomes. Every close friend I ever had I taught how to purify there own gear for there own health and well being but mostly to watch the expression on there faces and the proud look they display the very first time "there cup runnith over"   
You post is a well written and descriptive Good job sounds like you are a very articulate bee.
This post would be a very good start for anyone just breaking into this subject...

Tighten Up!  (UH)
 
 
 
 
    Prepuce
(Hive Bee)
11-09-04 05:17
No 540580
User Picture 
      Nothing new, huh?     

Jacked, I'm sure you're right that there is nothing new in the procedure I posted. To me it seemed like there was, probably because I misunderstood some of what I've read previously. At any rate I didn't expect that bees like you would learn anything from it.

I think I still have to take just a little exception with you on the idea that the process produces lower quality crystals. You can believe me when I say that I've made the full range, one end of the spectrum to the other, so I know dirty crystals when I see them. I think the best way to make my real point, here, is just to say that the method works really well. Certainly, if you stop the process after a half an hour you aren't going to get anywhere near the best you can get!

Well, I was going to try to make this nice and concise but I guess I'm just not capable of that. Thanks for all the replies, and the advice, Jacked. You've always been one of the good guys around here.

PP
 
 
 
 
    placebo
(arrogant bee of the day)
11-09-04 09:15
No 540612
User Picture 
      A good write-up none the less     

A good write-up none the less

It's not really me, it's Android in disguise!
 
 
 
 
    Prepuce
(Hive Bee)
11-12-04 06:25
No 541171
User Picture 
      Ghetto filter augmentation     

Dased,

Just re-read your post here, and the point of it suddenly sunk in. I like the setup, but SWIP is not sure he understands the benefit of the ceramic filter. Is it especially useful for any particular application?

While ugly your setup may be, SWIP has an alternative that is at least as crude, but also quite effective. Until now he's avoided posting about it, even though he uses it frequently. SWIP doesn't have means of drawing a picture readily available, so he asked me to describe it in enough technical detail, hopefully, to get the idea across.

Set up your funnel with filter paper, charmin plug, whatever you happen to be using. Pour in your solution as always, but don't get the funnel too full. As the filter begins to clog and the flow diminishes, reach for your turkey baster and yank the rubber bulb off. Take the rubber bulb and squeeze it about halfway, then stick the open end into the funnel, into the pool of solution. Release pressure on the bulb slowly, drawing most of the solution into it. Push down firmly until the open end of the bulb seals against the funnel, and begin squeezing gently. When finished throw it into the corner or the sink or wherever, and try to remember to wash the damn thing before you use it again. At least shake off the loose dirt!

PP
 
 
 
 
    dasedbee
(Stranger)
11-12-04 23:52
No 541299
User Picture 
      Ghetto filters     

The subject of carbon filtration was brought up, with the detractor being the absorption of the "mother liquid". The ceramic filter (it looks more like a wet rock, shaped like the dart sharpeners) has the positive of very fine filtration as well was not absorbing the solution. The ceramic filter removes much finer particles than any OTC filter paper readily available here in the country. (We have to pump daylight in.) Swidb's anal-retentive enough he was looking for a filter that wouldn't leave the occasional paper fiber.
Since it is normally saturated with gas, the material is unlikely to breakdown in most environments (so swidb's thinking went). Swidb reuses the filter after back-flushing with acetone cleanings, if needed. The updated version uses vacuum to perform the same function by using a liquid trap made from an Erlenmeyer with a 2 hole stopper. A hose is run thru the stopper to the bottom of the flask while the suction is applied to the second hole in the stopper. A pretty clasic water trap.The push-pull advocates use a similar setup on their first container.

happy filtration - DB
 
 

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