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Author: Subject: Rotovap quesions
themysteryman
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[*] posted on 6-1-2012 at 20:15
Rotovap quesions


I'm planning on doing an overhaul of my gear. I currently have an older analog buchi rotovap with diagonal condenser. I plan on purchasing one of the newer digital models with all digital controls and and vacuum controller. I was just wounding if someone could answer a few questions for me.

- With the newer, accurate digital Rotavapors is it possible to distill something you would normally need a manually distill with a fractionating column?

I also noticed they make glassware that you can do reflux reactions with (http://www.mybuchi.com/Glass-assembly-S-vertical-ref.7488.0....)

- Is it practical to use a rotavap for refluxing over - a hot plate/magnetic stirrer combination?

Any feedback would be appreciated!
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Dr.Bob
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[*] posted on 6-1-2012 at 21:26


A rotovap is not designed for fractionating anything, it is designed to remove solvents quickly. So it is nearly useless for distilling mixtures apart, unless they are trivial to separate.

The digital ones don't work any different than the manual ones, except break more often. I have used a number of models, and they all evaporate solvents fine. The digital stuff is not much help.

I also would not reflux stuff in them. They cost too much to use for that, when a heating mantle and condenser cost a fraction of what a rotovap does. Plus most rotovaps are dirty after a while, and if you reflux anything in them, you will clean the condenser and end up with crud in your reaction.

If you want to heat and stir a reaction at moderate temps, you can use the water bath to heat a flask while it rotates with out the vacuum connected. I have done that a few times when I need to dissolve something in a flammable solvent without using a hot plate. (No working steam lines...)

I cannot imagine using a hotplate with a rotovap, it already spins to stir, and has a water bath for safety. Don't mess with the design y changing it.

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themysteryman
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[*] posted on 6-1-2012 at 21:34


Quote: Originally posted by Dr.Bob  
A rotovap is not designed for fractionating anything, it is designed to remove solvents quickly. So it is nearly useless for distilling mixtures apart, unless they are trivial to separate.

The digital ones don't work any different than the manual ones, except break more often. I have used a number of models, and they all evaporate solvents fine. The digital stuff is not much help.

I also would not reflux stuff in them. They cost too much to use for that, when a heating mantle and condenser cost a fraction of what a rotovap does. Plus most rotovaps are dirty after a while, and if you reflux anything in them, you will clean the condenser and end up with crud in your reaction.

If you want to heat and stir a reaction at moderate temps, you can use the water bath to heat a flask while it rotates with out the vacuum connected. I have done that a few times when I need to dissolve something in a flammable solvent without using a hot plate. (No working steam lines...)

I cannot imagine using a hotplate with a rotovap, it already spins to stir, and has a water bath for safety. Don't mess with the design y changing it.



Thank you! I meant use my standard glassware with the hotplate/stir combo, not use the hotplate instead of a water bath.
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Hexavalent
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[*] posted on 8-1-2012 at 08:53


Can anyone point me to a source for a rotavap, cheaply? I've come to the point that every organic chemist reaches when he or she needs such a gadget!



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[*] posted on 8-1-2012 at 08:58


Quote:
Can anyone point me to a source for a rotavap, cheaply

All the info on these pages is free!

P
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Lambda-Eyde
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[*] posted on 8-1-2012 at 08:59


Depends on what you mean by "cheaply". If you're really lucky, you might be able to get a complete older model on eBay for anything from 400 to 700 USD. Rotavaps don't come cheap except for very rare cases...

Edit: Haha, I read in another post that you're thirteen? :D Now, a 13-year old with a rotavap, that would be something unique! I mean no offense though, I envy anyone who has a rotavap at that age!

[Edited on 8-1-2012 by Lambda-Eyde]




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Hexavalent
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[*] posted on 8-1-2012 at 09:02


Would it be cheaper to buy all the parts separately?



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Lambda-Eyde
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[*] posted on 8-1-2012 at 09:07


Probably yes, probably no. I've seen the motors go for below 100$ on eBay, but the condensers go for waaay more than that. Then you have to get a heating bath, and also the ring stand. Problem is that you have to be sure that all the parts are compatible and working properly (I actually don't know about the differences between B├╝chi models, perhaps someone could clarify this). The flasks aren't cheap on their own, either. So, then you have to narrow it down to a specific brand and model, and an affordable price. It could probably take years with constant surveillance of eBay to gather all those bits.



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Hexavalent
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[*] posted on 8-1-2012 at 09:11


The only thing you really need is the motor, and maybe the ringstand. Couldn't you set up your own heating bath, use your own condenser and bump trap and solvent collector?



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Pulverulescent
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[*] posted on 8-1-2012 at 09:16


I don't own a rotovap . . . (sniff!)
But then, why the fuck would I need one?

P
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Hexavalent
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[*] posted on 8-1-2012 at 09:17


Do you do inorganic or organic chemistry mainly?



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Pulverulescent
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[*] posted on 8-1-2012 at 09:24


I kinda just fuck around with mixed acid and various substrates, mostly!
BTW, ring stand . . . ?
What ring stand?

P
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[*] posted on 8-1-2012 at 09:30


The ring stand that holds up the motor and the solvent collector.



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Lambda-Eyde
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[*] posted on 8-1-2012 at 09:40


Quote: Originally posted by Pulverulescent  
I don't own a rotovap . . . (sniff!)
But then, why the fuck would I need one?

P

Well, you don't need a car, or a house, or two kidneys - but they sure as hell make life easier, less tedious and considerably more enjoyable!

Quote: Originally posted by Hexavalent  
The only thing you really need is the motor, and maybe the ringstand. Couldn't you set up your own heating bath, use your own condenser and bump trap and solvent collector?

No, as most rotavap condensers have the vapor tube integrated into them - ie the tube that goes through the motor and makes a vacuum-tight seal. Some have the condenser connected to a separate vapor tube with a ground glass joint, but I highly doubt those are standard sizes that you could get a condenser or an adapter for. Also, you'd need a very efficient condenser to handle the large volumes of low-boiling vapors, which would cost a lot anyways. The heating baths are really neat to have, but obviously any water bath would be a suitable replacement. But (at least to myself) there's a point in the rotavap that it should be ready to serve its duty at any time, and running parallel with whatever you have going on so that you don't have to assemble the condenser, set up the hotplate and water bath etc. each time you're going to use it.

Besides, half the point of owning a rotavap is to stare at those incredible coils when you're waiting for your solvent to come off... Right? ;)

Quote: Originally posted by Pulverulescent  

BTW, ring stand . . . ?
What ring stand?

P

Mind you, English is not my native language. :P I pondered quite a bit on what word to use, but "stand" sounded... silly, and I couldn't think of anything else. Besides, I'm used to seeing those advertised as "ring stands" irregardless of whether they come with an actual ring or not.

Oh, and P/H, is your change of name being accompanied with a personality change..?




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[*] posted on 8-1-2012 at 09:51


Don't worry about English not being your first language, you are doing very well and we all understand clearly what you are saying. What does P/H mean though?



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[*] posted on 8-1-2012 at 09:56


Quote: Originally posted by Hexavalent  
Don't worry about English not being your first language, you are doing very well and we all understand clearly what you are saying. What does P/H mean though?

Yeah yeah, I know that. It's just that a few technical terms don't translate well from Norwegian. P/H is Pulveresc-whatever/hissingnoise, his other nickname.

Edit: LOL, I just remembered that "irregardless" isn't a word! Probably made a few of you out there to poke out your eyes with a fork, eh? :D

[Edited on 8-1-2012 by Lambda-Eyde]




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[*] posted on 8-1-2012 at 10:03


I assume the condenser for a rotavap is also thick-walled for vacuum resistance?



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[*] posted on 8-1-2012 at 10:05


I also feel special now that I've got two stars:)



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[*] posted on 8-1-2012 at 13:43


Quote:
Oh, and P/H, is your change of name being accompanied with a personality change..?

I can't change something I don't have, now can I? :D

P
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[*] posted on 8-1-2012 at 14:39


Quote: Originally posted by Hexavalent  
I assume the condenser for a rotavap is also thick-walled for vacuum resistance?


Most brands, if not all, of lab glassware regarding condensers and such are designed for vacuum applications. Personally never seen a "for vacuum made" condenser next to a "regular" condenser in any of the renown glassware producers.

A rotavap is fairly easy and cheap to compile from "junkyard" stuff and some special glassware, as the vapor duct, and a good vacuum seal. Any other parts may be machined and adapted.

As regards to the newer age rotavaps I see few advantages, and a vacuum controller and a thermometer may be applied to almost any old ones out there. The Buchi RE-111 is a good one and I used it alot over the years.

Also have a miniature one, a Buchi Rotavapor -M set up just for show in reflux configuration (pic)

IMAG0357resize.jpg - 257kB

with 14/20 tapering for the small stuff. Got it NOT cheap of ebay.de (greedy germans...)

Incidently I need parts for it as I just discovered that one of the tapers had just cracked upon standing, not depicting the broken one.. (pic)

IMG_2102resize.jpg - 126kB

This piece of glassware have a SVL 22 thread of what I could research is a Pyrex invention. Already bought one from a member here, actually the one that broke though I doubt the it was faulty from him, more a heavy usage on my part.

Highjacking this post with a request of parts for this specific rotavap..., with flasks and the threaded taper adapter as the most demanded items.



PS. Also seen rotavaps been used for fractional distillations but with a hell of equipment attached and a very long heavy-duty Vigreux condenser...




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[*] posted on 10-1-2012 at 01:23


the beauty of the re111 is the vertical condenser, better though with the ground glass condenser (b-40?) than with those annoying black connectors.
the vertical orientation allows for a far shorter vapour duct, which in turn allows for greater/simpler flexibility for modification.
for reactions that stir poorly setting it up for reflux is often the best way to go about them.
i might start a rotovap modification thread if there are many around who like me constanty change their setups.
after years of naffing around i finally only a few weeks ago achieved a home made seal over the vapour duct far superior to the buchi one, which always pissed me off. it acheives a better vacuum, is made of teflon(ie better chemical resistance) and allows one to use any suitable sized bit of pipe for the vapour duct. the only thing i'm unsure of is if the strain on the motor is greater, however as my mechanical seal is teflon on teflon, vs buchi's rubber on glass, i think its fine, it seems to spin just as fast.
steam distillations are excellent on the re 111




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[*] posted on 10-1-2012 at 04:48


Quote: Originally posted by Panache  
after years of naffing around i finally only a few weeks ago achieved a home made seal over the vapour duct far superior to the buchi one, which always pissed me off. it acheives a better vacuum, is made of teflon(ie better chemical resistance) and allows one to use any suitable sized bit of pipe for the vapour duct. the only thing i'm unsure of is if the strain on the motor is greater, however as my mechanical seal is teflon on teflon, vs buchi's rubber on glass, i think its fine, it seems to spin just as fast.


Indulge me please, as I've got a "stiff" vapor duct gasket, so it only seals when it is heated somehow and I think it maybe just have reached its limit age-wise as it never has been changed since the rotavap was bought, atleast not in my knowledge.
My rotavap is not very much used just reasonable old so it is not regular wearing out of the gasket, I need a gasket I could make at home preferably.

PS. Would welcome a rotavap dedicated thread though I don't use it as much anymore, though I wish I did..:(
Too little time too little time...




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[*] posted on 10-1-2012 at 14:14


Anyone interested?

http://www.ebay.co.uk/itm/Buchi-B-465-Rotavapor-Water-Bath-P...




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[*] posted on 15-1-2012 at 04:48


Quote: Originally posted by bahamuth  
Quote: Originally posted by Panache  
after years of naffing around i finally only a few weeks ago achieved a home made seal over the vapour duct far superior to the buchi one, which always pissed me off. it acheives a better vacuum, is made of teflon(ie better chemical resistance) and allows one to use any suitable sized bit of pipe for the vapour duct. the only thing i'm unsure of is if the strain on the motor is greater, however as my mechanical seal is teflon on teflon, vs buchi's rubber on glass, i think its fine, it seems to spin just as fast.


Indulge me please, as I've got a "stiff" vapor duct gasket, so it only seals when it is heated somehow and I think it maybe just have reached its limit age-wise as it never has been changed since the rotavap was bought, atleast not in my knowledge.
My rotavap is not very much used just reasonable old so it is not regular wearing out of the gasket, I need a gasket I could make at home preferably.

PS. Would welcome a rotavap dedicated thread though I don't use it as much anymore, though I wish I did..:(
Too little time too little time...


Sorry for the slow reply, i had been waiting to have it apart this week for aphotogrph, hopefully tom.




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