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Topic: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation  (Read 5655 times)

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Offline themagicbean

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May I ask what is the role of each of the (aq) salts in the work-up (column chromatography)?  The only journal cites I can find are twenty years old and simply state in body text, without citation, as though it is too obvious.  (Desired product is organic, primary alcohol w/ benzene ring + dioxapentaring, DCM as solute.)

TPAP;  Tetrapropyl ammonium per ruthanate (http://en.wikipedia.org/wiki/Tetrapropylammonium_perruthenate)
NMO: N-mtehylmorhonone N-oxide (http://www.organic-chemistry.org/chemicals/oxidations/n-methylmorpholine-n-oxide-nmo.shtm)

Reactant + TPAP, NMO in DCM w/ 4A molecular sieve --> product -->
then column chromatography, again in DCM (with aqueous salts as above)

1.  NaS2O3:  Oxidizing?  Reoxidize RuO3 so that it is charged and can form salt complexes? 
    [Edit:  Reducing ... so ... found a link suggesting it complexes with transition metals, so it complexes w/ Ru (although my previous mechanism guess was wrong?) ]

2.  CuSO4:  Complexes well with pyridine so maybe complexes well with NMO?

3.  Brine:  Removes everything that is left.  (Overoxidized acids?)

And any anion is removing the tetrapropylammonium? 

Thank you!

[Various edits, not bracketed, after first comment.]
« Last Edit: October 13, 2014, 07:16:46 AM by themagicbean »

Offline Hunter2

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Re: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation
« Reply #1 on: October 13, 2014, 06:44:48 AM »
Better is to post the procedure and for what TPAP and NMO stands for.

Thiosulfat is more a reducer not a oxidiser.

Offline themagicbean

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Re: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation
« Reply #2 on: October 13, 2014, 07:14:35 AM »
I've edited to try to explain more completely, thank you.

Offline C-hemCards

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Re: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation
« Reply #3 on: October 13, 2014, 09:26:56 PM »
Do you mean Na2S2O3? That would be expected for this reaction, as Na2S2O3 is a reducing agent. Likely added to reduce any remaining NMO and perruthenate ion. Essentially, it's quenching the reaction.

Not sure what the CuSO4 may be doing. I've never seen that in a TPAP workup. May help with removal of the Ru salts, but that is just speculation. Of course, then you're hung with Cu entrained in your material...

A brine wash at the end of a workup usually provides a preliminary drying of the organic layer. This is usually followed by treatment with a more powerful solid drying agent (MgSO4 or NaSO4), then filtration of that solid drying agent away from the solution, concentration of the filtrate to an oil/solid, and chromatography.
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Offline Dan

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Re: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation
« Reply #4 on: October 14, 2014, 03:36:38 AM »
Reactant + TPAP, NMO in DCM w/ 4A molecular sieve --> product -->
then column chromatography, again in DCM (with aqueous salts as above)

Can you explain the experimental procedure clearly and in chronological order? To me this implies that chromatography is performed with DCM+CuSO4+Na2S2O3+brine - that does not make sense.

Presumably the crude is first washed with aqueous solutions of each of these salts, then the organic fraction is concentrated and the residue purified by chromatography. Is that right?

As has been mentioned, the thiosulfate is to reduce the NMO to N-methylmorpholine, quenching the reaction.

I guess, as you alluded to, that CuSO4 is used to chelate the amine byproduct (N-methylmorpholine) and take it into the aqueous layer.

As has been mentioned, the brine wash is for removal of water from the organic layer.
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Offline themagicbean

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Re: Role of work-up (NaS203, CuSO4, Brine) after TPAP + NMO Oxidation
« Reply #5 on: October 14, 2014, 06:38:07 AM »
"Presumably the crude is first washed with aqueous solutions of each of these salts, then the organic fraction is concentrated and the residue purified by chromatography. Is that right?"

Yes, correct, my apologies if it was not clear, sorry I've been a bit sick and out of it.

(1) Reaction  (Reactant + TPAP and NMO in DCM w/ 4A sieve)
(2) Resulting crude into separatory funnel.  Washes with three aq. salts in the order described  (and yes Na2S2O3, thank you). 
(3) Remove and dry with MgSO4 (from here I am good, but yes, it seems like brine was for early drying)
(4) Sintered glass filtration, then column chromatography

My questions are focused on step 2 and it seems as though you have answered them, thank you. 

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