06-23-00 18:49
No 20559
A bee I know is having trouble with vacuum dist extraction of MDP2P from MMs Methanol based Benzo Wacker.
When trying to vac extract at about 40C, boiling material foams over carrying with it most potential product. How does said bee prevent foaming?
(Chief Bee)
06-23-00 18:55
No 20564
It is hard to prevent foaming[1]. You just need to use a larger flask[2] until the foaming has stopped, then change to a smaller.
[1] Using a lower vacuum gives less foaming, but this is not always suitable.
[2] Or divide your mixture into several portions and process separately.
http://rhodium.lycaeum.org
(Newbee)
06-23-00 19:08
No 20571
Yeah...larger flask was said bee's next step.
Roughly speaking, how light in color should the methanol benzo product bee after washes (before vac dist)? Said bee doesn't see much separation after NaOH washes.
Is BS's method using DMF any easier/cleaner?
It seems like too many solids remain even after vaccum filtration resulting in high viscosity which produces the foam as DCM tries to become vapor.
(Stranger)
06-25-00 06:41
No 21108
On the contrary..SWIM would recommend a SMALLER flask. She experienced the same damn problem..with MM's workup...and for a few weeks SWIM had clumps of hair missing from her head from the frustration. Anyway..just a few notes..
When heating reaction...make little 4mm twists of the dial to SLOWLY reach the reflux temp..dont overheat EVER!!
Fall asleep and leave the reaction longer than 8hrs...expect tar.
Do RXN, cleanup and distillation in one day..work quickly and try not to let things sit at all.
If you end up with 300mL crude oil...use a 500mL RB, and immerse about 70% in. safflower oil... Distill slowly. Add Ice. Enjoy.
(Just SWIM's opinion but it seems that the foam appears when the liquid is not stirred efficiently. When the liquid is in a smaller flask and being stirrered constantly..the exposed surface area of the oil doesnt form a "skin".. thus preventing the foam) You might also try distilling in two smaller portions instead of one large one.
If all else fails...use a claisen and distill...or do the bisulfite and use that w/o distilling at all.
BTW- MM's Post wacker color: deep red with a lovely spicy bouquet.
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(Newbee)
06-26-00 19:09
No 21771
Hey thanks alot! I know what you mean about the loss of hair. 3 day scratching the head wondering what she's doing wrong.
(Newbee)
06-26-00 19:34
No 21776
Hey, I did search on bisulfite method an can't find any details. Can someone point the right direction?
(Stranger)
10-25-02 14:45
No 372528
The wacker ala MM has proven to be a lesson in frustration, afoaf does not own a stirer hotplate combe so has his flask's heated in a shallow fryer with mag stiring from underneath, also doesn't own a distilation column, just flask ->distilation head-> condensor.
He after what he assumes was successful wacker, as all behaved as described and all noted observations matched those posted, ie color changes in wash's, scumm emulsion etc.
After seperation Dcm/Ketone was fired into 1l rbf, 1" stirbar. The vac source applied, aspirator, with the aid of autogauge showed to pull 27"merc. Same as used for safrole dist. What happened next is still shitting him, The DCM came off no probs, then some heat was applied (perhaps a little to fast, to much, oil bath about 60deg.
Some water came over, as noted by vapour temp, then the whole contents of flask foamed over massively. Oh the safflower oil was added as buffer (?) The mess was back washed into the flask with some distilled water(? not a great choice)
The Ketone in the flask before the h20 was added looked as brown as earlier just foamed onto side of flask. This was then tried again, same thing happened once water had been removed. Contents stay dark until foaming starts then turn yellow, then back to dark once vac source is pulled.
So to finally get to some point here, if afoaf has degraded ketone, ie fucked, how does it behave?
how quickly does the ketone from the wacker have to be seperated?
Does it have to be constantly cold to stop it decomposing? Then when and if it is ketone, which by observation and workup is assumed so, how sensitive to the distillation process is it?
Has he ruined it by heating?
How fast is to fast to heat to bp, and what happens to ketone when heated rapidly?
Everyone keeps saying heat slowly to temp over two hours, what increments in temp are we talking here?
Well there are many more questions, he will try what was mentioned about smaller amount in flask and see if this helps in this instance. The whole incident performed for educational purposes has carved a runway in the carpet from the mad pacing back and forth,
You dont learn from doing things the right way, coz if you did you would already know it.
Keen for some feedback, tired, frustrated, amused and confused.
Happy ?
(Hive Bee)
10-25-02 16:14
No 372548
My oil bath temp when K starts to come over is usually 150-160 C. (with 29 + vacuum) Have you measured temp inside still head? Sounds like your oil bath is no where's near hot enough. I get K between 102-105 C. Don't forget there's a differential between oil bath temp and temp inside the RB flask. (That is, temp inside flask is LESS than oil bath)
There's no getting around some splashing/foaming, however, a long Vigreux column is ESSENTIAL! SWIM's best is 450 mm long and has 3X the "normal" number of indentations. I've actually found that spinning the stor bar at a lower speed, say at 3, instead of max helps reduce splash over.
To do a Wacker and cleaning and distill in one day is alot of work. Mistakes happen and you can get impatient when rushed for time. SWIM splits his into:
Day 1: Wacker - refridge product.
Day 2: Wacker cleanup - refridge product.
Day 3: Distill K - refridge product.
Nice slow pace makes for less mistakes...
(Stranger)
10-27-02 12:17
No 373182
Thanks for the feedback.. I was not aware of the thermo lag between bath and flask.. And yes the temp in the distill head was measured the whole time.. that was how i new the water was coming over at about 59-61 deg C at 27"Hg. Upon inspection of contents of boiling flask, there seems to be some sort of crystall formation on side walls of flask.. they look whitish??? have collected some yellow green liquid that was floating atop some water in collection flask..
Does ketone dissolve in water at all?
So basically I have to have my oil bath 30 or so degrees higher than the boiling point of my desired fraction, is that right?
How can you tell when your raw ketone has been killed in a distillation attempt, what conditions are to harsh for it?
Am working with aspirator off tap water pressure so vac is between 26"Hg and 27"Hg. Will attempt to distill other portion that was set aside and compare with previous run.
Thanks again
Happy ?
(Hive Bee)
10-27-02 13:00
No 373188
In some cases you can add surfactants that boil off at lower temps (not in this case) like tert-butanol.
Since you don't have adequate stirring t may be suggested you connect your vacum to a needle valve, in line with manometer, or pressure gauge (capable of reading vacumns or negative pressures such as those used in HVAC) once you have this modification hooked up to your trap, or vacumn nozzle then, you can reduce your vacumn as needed until the frothing subsides.
E.G. open the valve to let air into the system, then close again and repeat as many times as is nessecary to break the foam.
Also if bumping is a problem you can rig a capillary tube going into your distilling flask as a sort of ghetto gas inlet.
This too can be connected to a valve to regulate airflow into the capillary.
(Newbee)
10-27-02 20:37
No 373253
dwolf,
1) what temp did safrole come over at?
look at the chart on the safrole distillation document on rhodium's site.
basically, you need 28" to pull safrole at 140C and ketone 40C higher at 180C.
ketone tends to burn over 200C in the flask. dunno about the frothing though, try turning down the aspirator?
using an electric water pump to boost your aspirator, acquiring a refrigerator compressor, and buying a real friggin' vacuum pump for $200 are all covered in other threads.
(Hive Bee)
10-28-02 09:08
No 373516
I have put at least 20 posts about distillation of ketone on the Hive. UTFSE!!!