January 24, 2021, 04:24:39 PM
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Topic: Purity of acid chlorides from thionyl chloride  (Read 454 times)

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Offline Reddart

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Purity of acid chlorides from thionyl chloride
« on: December 08, 2020, 08:32:52 PM »
I have always used oxalyl chloride (CH2Cl2, drop of DMF) to make acid chlorides in the past. Always end up clean enough to use by just pumping off the solvent and excess oxalyl chloride.

Since I now need to use thionyl chloride for cost reasons, will it be clean enough to use by just evaporating the excess thionyl chloride (using excess as the solvent, no other cosolvent)? The product chloride should be relatively non volatile compared to thionyl chloride.   

Offline rolnor

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Re: Purity of acid chlorides from thionyl chloride
« Reply #1 on: December 09, 2020, 11:13:15 AM »
I dont see any problem, the reagent and by-products are volatile.

Offline Reddart

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Re: Purity of acid chlorides from thionyl chloride
« Reply #2 on: December 09, 2020, 11:59:57 AM »
I found a promising prep about this very topic: Vol. 75 No. 10 October 1998 • Journal of Chemical Education

Offline BobfromNC

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Re: Purity of acid chlorides from thionyl chloride
« Reply #3 on: December 09, 2020, 05:07:27 PM »
If you can put it under vacuum for a while after the rotovap, that should remove any traces of SOCl2.  I use both oxalyl chloride and thionyl choride, mostly following the prep I have, but I have alternated, and in most cases they both work fine.   Oxalyl seems a little gentler to me, but not on everything.

Offline mikeB

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Re: Purity of acid chlorides from thionyl chloride
« Reply #4 on: January 19, 2021, 02:15:06 AM »
After rotary evaporating the excess of thionyl chloride, I would dissolve the residue in toluene and rotary evaporate it. After repeating this for 2 or 3 more times the product is completely free of SOCl2.

--Mike
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--Mike
“ [Thermodynamics is] the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown. Einstein"

Offline Babcock_Hall

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Re: Purity of acid chlorides from thionyl chloride
« Reply #5 on: January 19, 2021, 09:45:15 AM »
mikeB, how did you decide to try toluene?

Offline mikeB

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Re: Purity of acid chlorides from thionyl chloride
« Reply #6 on: January 19, 2021, 06:14:40 PM »
High boiling point yet easily removed on a rotovap hooked up to a non-oil pump vacuum. Also non-reactive for my applications (amide couplings) so no need for extensive high vacuum drying.

--Mike
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--Mike
“ [Thermodynamics is] the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown. Einstein"

Offline mikeB

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Re: Purity of acid chlorides from thionyl chloride
« Reply #7 on: January 19, 2021, 06:18:13 PM »
Also the toluene-water azeotrope is an extra perk if you have acid-water (like HCl) to remove from your samples.

--Mike
Cheers,
--Mike
“ [Thermodynamics is] the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown. Einstein"

Offline hypervalent_iodine

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Re: Purity of acid chlorides from thionyl chloride
« Reply #8 on: January 19, 2021, 10:42:01 PM »
I've always found it to be quite straightforward. In the past I've removed excess with an aspirator. It should go without saying, but if you use a rotovap, take care to put in an internal trap between the condenser and pump to protect it from being chemically degraded.

Offline rolnor

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Re: Purity of acid chlorides from thionyl chloride
« Reply #9 on: January 20, 2021, 01:12:09 PM »
I have destroyd expensive pumps by distilling acid chlorides, I strongly suggest using aspirator. SOCl2 is not hard to remove in vacuo.

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