enter image description here

Hey folks,

so I've been wondering why the use of 5 equivalents of Et3N in this case of a Swern-oxidation is necessary. I have done this reaction succesfully quite a few times now, but all the literature uses 5 equivalents as well. I am fully aware of the mechanism (shown below). I can explain one eq. for the HCl that emerges in step one:enter image description here And in the second step we need the base to form the sulfurylide: enter image description here

but this should not be a equilibrium as the Ylide has no net charge and in my opinion is more stable. If it were to just enhance the reactivity a bit, I'd think that 2 more eq. (so 3 eq. in total) are sufficient.

I hope you can help me with this.

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    $\begingroup$ Have you tried the reaction with less equivs? Do you need extra to raise the pH especially in the presence of carbon dioxide? Is some trapped as a hemi-aminal? Just guesses ... $\endgroup$ – user1945827 Jul 2 '19 at 12:46
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    $\begingroup$ 3 equivalents of Et3N is stoichiometric. If the ylid is reversibly protonated by Et3N-HCl, why not use excess Et3N? It certainly isn't detrimental. Note that each successive reagent is in excess. $\endgroup$ – user55119 Jul 2 '19 at 15:03
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    $\begingroup$ If isn't broke don't fix it! Et3N is cheap. $\endgroup$ – Waylander Jul 2 '19 at 19:03

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