Author Topic: Ketone Distillation and Different Pumps Used  (Read 1627 times)

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TheBlindGenius

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Ketone Distillation and Different Pumps Used
« on: August 21, 2002, 10:32:00 AM »
The vacuum distillation of MDP2P must, of course, be done in a vacuum atmosphere or the ketone will polymerize at a certain temperature.  The temperature/vacuum correlation is not something that is easy to calculate.  In the real world, the numbers are often very different even from the figures given by the JAVA applet pressure/temp calculator at rhodium.ws.  In swim's observation, most bees use vacuum pumps like the "yellowjacket" that theoretically pump down to one micron or less and use pump oil and a cold trap, while some use water aspirators or recirculating water aspirators with pumps, etc.  Swim has often looked in his different catalogs at the many pumps offered, and one that is very appealing to him is the diaphragm vacuum pump.  For example, KNF and Vacuubrand are the most noted.  Swim likes these pumps because they are easy to clean, don't require pump oil, can take a good amount of oil or water vapors without breaking, and are small and lightweight.  He has one that pulls 120 mmHg (that's what the catalog from the place he got it from says anyway) which he uses for vacuum filtration.  There is a small shop a few miles from swim's house that sells surplus or used scientific equipment, and they have a KNF pump that theoretically pulls 10 mmHg for $500, as well as more expensive ones ($1000+) that are rated for 6 mmHg and 1.5 mmHg.  swim was wondering if anyone had used these types of pumps to distill ketone, if they are a good choice, and if the 10mmHg one is good enough for the job.  The reason he asks is that it seems that vacuum pumps don't pull even close the amount they say they do.  There was a post by LabTop explaining why a long time ago.  Swim has been using metabisulfite as his way of purifying ketone, and the best color he can get this way is a yellow/light red color.  he would like to get purer ketone in the future.  Anyways, thanks for any comments.

Osmium

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The 10mbar (6.5mmHg!) pumps are borderline for ...
« Reply #1 on: August 21, 2002, 11:07:00 AM »
The 10mbar (6.5mmHg!) pumps are borderline for ketone. They will work sufficiently when your ketone isn't too contaminated with lots of tar, the pump isn't in need of maintainance and will reach that vacuum consistently, your apparatus is absolutely gastight and there's no water and not too much solvent residue in your ketone.
The lower than 10mbar pumps will work better for this task, and I wouldn't distill ketone with a pump that cannot go below 15...20mbar except in emergencies.
My recommendation is: distill ketone and product with oil pump, saf/iso and everything boiling below with diaphragm pump.

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TheBlindGenius

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Swim just called the place up, the guy put him on ...
« Reply #2 on: August 21, 2002, 11:27:00 AM »
Swim just called the place up, the guy put him on hold and called KNF.  He said that the pump is rated at 29.5" or 10 mmHg, or about 15 mbar.  He also said the pump is new so it doesn't need maintenance of course.  Swim's book TS2 features a girl distilling a 500g DMF/O2 Wacker at only like 75 or 100mmHg.  Check it out, it's there.  How the fuck did she do that, if now your telling me that 6.5mmHg is borderline?  I'm not contradicting you, I just don't get how she did that.  Maybe if swim uses a 10/30 jointed thermometer into a 10/30 jointed still head instead of using a regular thermometer and a thermometer adapter, the apparatus will be more leak-tight, right?  Anyways, if swim has money he will buy both that and an oil pump later this year.  about the oil pump, can someone recommend a certain brand that does the job but isn't too expensive? if swim spends the money on both, he wants the oil pump to be able to distill the ketone at below 90 or 100 deg, that way a water bath can be used instead of an oil bath.  However, wouldn't a high vacuum cause the difference in bp's between isosafrole and ketone to be very small?  so maybe borderline is good??  :P

Bubbleplate

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Besides A Good Vacuum Pump
« Reply #3 on: August 21, 2002, 12:58:00 PM »
Don't forget to pay attention to the other factors: like good glassware setup. With high boiling temp materials like oils, ketone, etc. the shorter the distillation path, the less re-condesation back into the flask you'll get. Get a good distillation column like a Vigreux and insulate it well with foil, fiberglass, etc. Better yet, try and beg/borow/steal a Vacuum Jacketed/Silvered column. Those columns really work wonders!
Don't kid yourself - the deeper the vacuum, the easier it will be to boil a given product. The absolute boiling point temperature will be LOWER with more vacuum, but that doesn't change (for the most part) the difference in bp between two materials.

If they drive God from the earth, we shall shelter Him underground - Dostoevsky

TheBlindGenius

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Glassware setup
« Reply #4 on: August 21, 2002, 05:24:00 PM »
I'm sorry, I don't quite comprehend.  Do you WANT a short distillation path or not?  It sounds like you do.  But if you do, why use a column?  Aboutt vacuum jacketed silvered columns.... If swim had the money he would get one  :P .  Swim's glassware source doesn't carry them, unfortunately, and they aren't used in his university's O. Chem I lab so he couldn't borrow it either.  And if you are going to use a column, wouldn't you need a variable reflux distillation head/receiver setup ($500+)?

hCiLdOdUeDn

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I think osmium was talking about 6.
« Reply #5 on: August 21, 2002, 05:29:00 PM »
I think osmium was talking about 6.5mm HG being borderline because then it will be easier to distill the impurities such as tar. IMO 40mm HG produces purer Ketone than 6mm HG

hcildoduedn

TheBlindGenius

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Huh?
« Reply #6 on: August 21, 2002, 05:36:00 PM »
I'm sorry, I don't know much about the whole distillation thing except what I have read in TS2 and Zubrick, so if I come off retarded, don't break my balls.  But, wouldn't you not have to distill the tar?  Wouldn't you just let the ketone come over, turn the heat off and let the tar sit in the distillation flask?  See, I was thinkin' what you were thinkin'.  It might not be right, but I know for a fact that reducing pressure reduces the difference between bp's.  It's not very drastic, but it does happen, right?  So, if you have the largest poosible difference between say the bp's of isosafrole and ketone, without the bp being so high that it polymerizes, then it would be easier to distinguish the two fractions because the temp would jump up, right?  Or not?

Nemo_Tenetur

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Batch size is also important
« Reply #7 on: August 22, 2002, 12:56:00 AM »
I want to add here two things:
IMHO, the batch size is also an important factor. If you want to distill a huge quantity ketone you need up to hours heating. It seems logical that hours heating produces more tar than a few minutes heating for a small-scale batch. I've distilled MDP2B with a somewhat higher boiling point than MDP2P in a small scale (less than 50 ml) with a water pump without problems. On the other hand, a kilo-batch 4-methoxy-APP was destroyed under membrane pump conditions, whereas this compound can be distilled even with a water pump in a small scale without problems.

The second thing is: make sure that your diaphragm pump is chemical resistant. Most pump producers sell two different pump types: a "normal" edition and a chemical resistant one (teflon coated).


noj

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The higher the vacuum, the lower the distillation ...
« Reply #8 on: August 22, 2002, 08:27:00 PM »
The higher the vacuum, the lower the distillation temperature, and the smaller the distance between fractions

I don't understand how the distance between fractions can get smaller. It should remain consistant as long as the pressure remains consistant.

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TheBlindGenius

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Distance between fractions
« Reply #9 on: August 23, 2002, 12:15:00 PM »
Swim doesn't understand it either, but it definitely happens.  there's more info on it on TFSE or in Zubrick's book.  BTW, about how many mmHg does a water pump pull?  Is a water pump the same as an aspirator?

Bubbleplate

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A Water Pump Is NOT The Same As An Aspirator
« Reply #10 on: August 23, 2002, 01:09:00 PM »
An Aspirator a device based on the "Venturi Effect" in which a moving fluid (H2O) in a tube with a smaller diameter is inserted a very short distance into a tube of a larger diameter (Aspirator). [See

http://www.coleopsoc.org/scarabs/scarabs_9.pdf

] The moving water when you turn on the faucet will suck air, i.e. create a vacuum.
A water pump could be one of many things, but typically is a device powered by an electric motor that turns an impeller (turning fan-like water wheel) that "scoops" the water through an intake port and out the discharge port.
The two can be combined quite effectively (A high speed water pump like a Sump pump with an Aspirator) to create an excellent quality vacuum device. (Mine pulls almost 29") You can make it "self contained" ; i.e. in a 5 gallon bucket and the water gets re-circulated over and over. Adding ice to the water will increase the strength of the vacuum.
Rhodiums Web site has an example of this:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/equipment/aspirator.html



If they drive God from the earth, we shall shelter Him underground - Dostoevsky

locrian

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I don't understand how the distance between ...
« Reply #11 on: August 28, 2002, 05:44:00 AM »
I don't understand how the distance between fractions can get smaller. It should remain consistant as long as the pressure remains consistant.

Um, how do you figure that?  The way I see it (and mind you I have no source to back this up, I'm guessing but it makes sense to me) atmosphere is reduced proportionally through use of suction or vacuum.  Atmosphere is literally being pulled out of the setup.  And its not like your vacuum is going to only selectively remove cooler atmosphere first, I can't think of why that would occur.  I think your looking at it like a teacher's "bell curve" as they mislabel it.  You know, where every test grade gets lifted up by the same number of points it took to make the highest grade 100%.  Rather think of it as a spring.  When left alone and looked at from the side you see even spacing in the coil.  When you push the spring down, the spacing still remains even - proportional, its not like the bottom part collapses first.  Again though, I could be totally wrong, I'm only guessing at what seems logical.   :P