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Author Topic: DCM instead of toluene/xylene in al/hg amination  (Read 135 times)

igotthere

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DCM instead of toluene/xylene in al/hg amination
« on: December 23, 2012, 12:36:27 AM »
Will DCM work as my extraction solvent when extracting from post NaOH addition reaction mess?
And can I just wash/dry then gas as per xylene?

thx


igt

jon

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #1 on: December 23, 2012, 02:29:08 AM »
no  i think it dissolves hydrochlorides.

lugh

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #2 on: December 23, 2012, 04:57:18 AM »
It also tends to form emulsions  8)
Chemistry is our Covalent Bond

pbinteger

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #3 on: December 23, 2012, 05:11:57 AM »
But also -- Toluene tends to form more of an azeotrope with water during workup so it's important to dry it before gassing it or you may have trouble forming xtals -- I recommend evaporating ~5% of your extraction to get rid of water.

igotthere

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #4 on: December 23, 2012, 03:46:19 PM »
thanks guys

RoidRage

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #5 on: December 24, 2012, 09:58:17 AM »
Quote from: pbinteger on December 23, 2012, 05:11:57 AM
But also -- Toluene tends to form more of an azeotrope with water during workup so it's important to dry it before gassing it or you may have trouble forming xtals -- I recommend evaporating ~5% of your extraction to get rid of water.

It's well known that water forms an azeotrope with toluene but does that actually makes the toluene harder to dry with desiccating agents when compared to others non azeotrope-forming non-polar solvents? I really don't think so to be honest.  And if I'm wrong, I'd really like to get the explanations :D

pbinteger

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Re: DCM instead of toluene/xylene in al/hg amination
« Reply #6 on: December 24, 2012, 04:29:44 PM »
The problem with common using drying agents is there's no solid indicator that you've got all the water out, and they don't actually get all of the water out. Na2SO4 or mgso4 should be used to pre-dry the solvent before drying it over heat with Na/benzophenone. Then it should be stored over 3A sieves. I know that seems extreme but Toluene in particular will hold about 225ppm h2o even after using common drying agents. At the very least the Freebase / Toluene extract should be dried over 3A sieves for 24 hours before gassing -- that should bring h2o down to the double digits ppm.

 
« Last Edit: December 24, 2012, 04:44:19 PM by pbinteger »
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