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I am trying to form 2,2-diacetoxy acid using acetic anhydride and glyoxylic acid monohydrate (Scheme below)

enter image description here

I could not find a suitable synthetic protocol for this, so I just added 10 equivalents of acetic anhydride to 1 equiv. of glyoxylic acid monohydrate and refluxed the mixture at 140 °C. Now the limiting agent (glyoxylic acid monohydrate) is gone, but I am not sure with how to remove excess acetic anhydride; its boiling point is too high (139.8 °C) and the pressure of the rotovap in my lab isn't that strong (I tried removing toluene before, it only worked when I increased the water bath temperature to 70 °C).

Yes, I am aware that I can make an azetrope by adding toluene, which will have a lower boiling point, but that would still require the water bath temperature to be quite high and I'm scared that my product might be broken down or perturbed at such a high temperature. Should I add ~2 N HCl and extract my product with DCM? Any other tips or guidance? I'd appreciate any help.

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  • $\begingroup$ If you have access to a good vacuum pump (~30-50 torr) you probably should try fractional vacuum distillation. $\endgroup$ – permeakra Jun 30 '20 at 14:09
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    $\begingroup$ You refluxed the reaction mixture at 140C and you are now worried about a high water bath temperature? $\endgroup$ – Waylander Jun 30 '20 at 14:35
  • $\begingroup$ @Waylander you are right, wasn't thinking straight $\endgroup$ – chemrese Jun 30 '20 at 23:48
  • $\begingroup$ @Waylander I made an azetrope with toluene but still can't distill it off. Would adding ~2 N HCl followed by extraction with DCM do? $\endgroup$ – chemrese Jul 1 '20 at 13:25
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    $\begingroup$ I think there is every chance the 2N HCl would hydrolyse the acetal. Can you get an vac pump? $\endgroup$ – Waylander Jul 1 '20 at 14:15

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