Hi,
I used oxalic acid to remove a ketal in a synthesis of (beta)cedrene.  The only thing i could get it to dissolve in was water or methanol.
Im not sure if you will be able to extract oxalic into a chlorinated dry cleaning solvent.    
Maybe worth a shot, but i dont think it will dissolve.  BTW oxalic isnt a nice reagent, it causes renal failure and attacks your CNS, so be careful with it.
Formic acid is a bit more soluble and migh be a better reagent to hit blood with in this case, but im not certain.
As to acid/acid reaction  

 .  Chemically speaking i think its unlikely, but dont quote me on that.
Hope this helps
Graeme
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