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Topic: reflux and distillation differences  (Read 9063 times)

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Offline jack2020

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reflux and distillation differences
« on: February 19, 2014, 02:38:00 PM »
hi all
I want to synthesize an organic compound which it should be refluxed for 2h in pyridine and then it should be disstilled to remove 2/3 of pyridine, how I can do it? I mean I should open the system after 2h and then change the condenser and system for distillation? isn't it dangerous due to low flash point of pyridine?
thanks for your help
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Offline kriggy

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Re: reflux and distillation differences
« Reply #1 on: February 19, 2014, 03:01:21 PM »
For reflux you use condenser like this one so the pyridine drops back to the flask. After 2hrs I think you can remove the pyridine by rotovap - vacuum lowers the boiling point so you reduce the risk of flame.
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Offline Corribus

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Re: reflux and distillation differences
« Reply #2 on: February 19, 2014, 03:26:21 PM »
I think a real vacuum distillation, with gentle heating, will be more efficient than a rotovap.
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Offline kriggy

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Re: reflux and distillation differences
« Reply #3 on: February 19, 2014, 03:57:47 PM »
Doesnt rotovap have vacuum? At least the one in my lab has it.
There might be mistake with naming those instruments on my side ofc.
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Offline jack2020

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Re: reflux and distillation differences
« Reply #4 on: February 20, 2014, 11:27:25 AM »
unfortunately our lab is very poor and we don't access vacuum even for our rotary so what do you think if I try to convert the reflux system to distillation system with changing the angel of condenser 90oC
because I think for reflux the condenser must be vertical but in distillation the condenser is horizontal, am I right?
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Offline discodermolide

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Re: reflux and distillation differences
« Reply #5 on: February 20, 2014, 11:32:58 AM »
Search the terms on Google, you should be able to find lots of images and perhaps videos as well describing what you want to do.
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Offline AlphaScent

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Re: reflux and distillation differences
« Reply #6 on: February 20, 2014, 11:51:59 AM »
My thoughts exactly disco. 

Distillation and evaporation are two different phenomena.  Look at each.

Distillation is going to be the better bet with pyridine.

My question to you is, What is the reaction?

 Pyridine usually serves a purpose in the reaction and is not present only for its solvent properties.  Either way you can use less pyridine or replace with a more volatile solvent which makes removing the solvent that much easier.
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Offline zsinger

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Re: reflux and distillation differences
« Reply #7 on: February 20, 2014, 03:06:03 PM »
Pyridine is a HCL sponge in the reaction :).  Using anion salts avoids the need for pyridine.
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Offline AlphaScent

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Re: reflux and distillation differences
« Reply #8 on: February 20, 2014, 03:38:51 PM »
The reaction is never stated.  You dont know for sure if it is a scavenger.  More information could be useful.
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Offline jack2020

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Re: reflux and distillation differences
« Reply #9 on: February 21, 2014, 03:35:54 AM »
thanks for the replies, let me not to speak about all details, I think zsinger is right because one of my reagents is a hydrochloride salt and probably the pyridine should act as HCl sponge, I have to use pyridine because it has been proved as the best solvent (poor me  :'(), so tell me how I can avoid the dangers of refluxing with pyridine and then distillation which should follow again with reflux.
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Offline jack2020

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Re: reflux and distillation differences
« Reply #10 on: February 21, 2014, 03:58:42 AM »
I have found a picture of 2 condenser which are oriented by 90 degree is it possible to set the first condenser for reflux and after 2h set the second condenser for distillation and after distillation compelation remove the second condenser to continue the reflux  ???

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Offline discodermolide

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Re: reflux and distillation differences
« Reply #11 on: February 21, 2014, 04:48:36 AM »
Sure it may be possible, but I would not advise it.
Just do the reflux. Then change the condenser to distillation, after cooling the reaction so that is no longer refluxing. Do the distillation and swap back again.
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Offline jack2020

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Re: reflux and distillation differences
« Reply #12 on: February 21, 2014, 05:29:07 AM »
yes, your solution is more wiser than mine :D
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Offline zsinger

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Re: reflux and distillation differences
« Reply #13 on: February 21, 2014, 01:36:55 PM »
Follow Disco's advice, and you shall receive product :). (Hopefully)
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