Still thinking this through…
So, Na2S + H2O -> 2Na+ plus SH- plus OH-
Now when excess Cl-CH3COO:Na is added, it will (should?) react with both SH- and OH- to (eventually) produce thiodiglycolate AND diglycolate.
Since I want to avoid producing diglycolic acid in favor of thiodiglycolic acid, and Na2S is also slightly soluble in alcohols, I was thinking that I should dissolve Na2S in ethanol and then add the Cl-CH3COO:Na. The product (thioglycolate and then thiodiglycolate) should be soluble in ethanol but at the same time the Na2S will be consumed slowly since it's only partially soluble in ethanol.
At first glance, this seems like a better way to avoid producing H2S or unnecessary glycolate. What do you think?