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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: zarhym on July 13, 2016, 08:46:01 AM

Title: I need some suggestions about sulfite esters.
Post by: zarhym on July 13, 2016, 08:46:01 AM

I have some problems about this synthesis.
1. I have some mixed results about the stability of this sulfite ester.
Sometimes I can  purify it through a silica column without decomposition. But it decomposed when the solvent is evaporated under reduced pressure at room temperature.
2. Many paper used aqueous Sat. NaHCO3 to quench excess thionyl chloride, and  I can wash the product with excess aqueous Sat. NaHCO3 followed with extraction with EtOAc. Although, the TLC indicates almost quantitative conversion of this reaction, it seems stable but the yield is too low when the solvent is all evaporated.  There are some white precipitations between EtOAc layer and aqueous layer. It looks like the product is decomposed since TLC test of aqueous layer indicates only starting material.   

The reactions uses about 3eq pyridine, 5eq SOCl2 and 10ml solvent /1g starting material . Is there anyway to remove excess SOCl2 and pyridine without having the product decomposed?
In your experience, is sulfite ester sensitive to water, acid,  base or temperature?

I need your suggestion about the workup and storage.

Thanks a Looot!

Title: Re: I need some suggestions about sulfite esters.
Post by: sjb on July 13, 2016, 09:42:25 AM

Typically I think you can use aqueous Cu(II) salts to wash away pyridine, though I'm not sure it would work in this case. Similarly, usually you can decompose excess thionyl chloride with methanol, but not sure of sulphite stability here.

Title: Re: I need some suggestions about sulfite esters.
Post by: wildfyr on July 13, 2016, 10:00:40 AM

Run a 2D TLC to really make sure its not decomposing? I wouldnt be surprised if its acid unstable and the silica gel is killing it. Also, when you quench SOCl2 with aqueous solution, it probably becomes acidic then. Don't use EtOAc to wash acidic solution, it can aldol condense and yield oligomeric BS.

You can distill off your solvent, excess SOCl2 and pyridine (DOUBLE TRAP). Whats left should be pdt and pyridine-HCl. The copper sulfate trick for pyridine is a great one, and can get any remaining pyridine/pyridine-HCl out, and the wash should be pretty neutral.