okay, to make it clear exactly what is occurring in this reaction, i think that the iodine is oxidising the ascorbic acid and in the process ionising - which then allows it to nab a hydrogen that the oxidising freed from the ascorbic acid. Have i grasped this correctly? The thing is, dehydroascorbic acid can be turned back into ascorbic acid, but the question is: does the hydriodic acid do this? Or in other words, is this an equilibrium reaction or does it only proceed in one direction. From everything i've looked at so far, it is one way, but i've not seen a lucid explanation of the reaction kinetics and i am not sure.
I thought about whether the hydriodic acid would react with the dehydroascorbic or ascorbic acids, and i can't see how that would happen, from what i understand of the HI reduction mechanism, it is more specific than some reaction mechanisms because the iodine's larger size. there is two hydroxyls on dehydroascorbic acid, but can they be reduced or not? likewise all those keto groups all over it.
if it were possible i imagine one would want to ensure that more than enough HI would form to bring the concentration up to 57%, perhaps do the reaction with 4 mol of I2 and 4 mol of ascorbic acid and 1 mol of ephedrine, and a neutral atmosphere to reduce the possibility of the ascorbic acid being oxidised by something other than the iodine. Or perhaps only the ascorbic acid needs to be in excess as it will regenerate any I2 that reforms. I thought about whether the ascorbic acid perhaps could be brought to melting point under a neutral atmosphere (that's 190 degrees) but that would be too high perhaps? also rhodium has been throwing around the idea of using anhydrous acetic acid as the reaction medium... Perhaps anhydrous acetic acid would be exactly the right environment to use ascorbic acid/I2 as an in situ source of HI...
edit: looking at rhodium's new idea's page... hypophosphorous/i2 reduction using anhydrous acetic acid... let's suggest another idea: could the HI azeotrope distillation be done so that one adds 5% acetic acid (vinegar) rather than dh20, and then fractionally distilling the water out first then bringing the HI across with the acetic acid. This might need to be dried further, maybe using a molecular polarity filter (molecular seive are they called?) or whatever...
and so then, you have HI dissolved in acetic acid sans water, if one uses an adequate excess of reagent, and gentle conditions, wouldn't this work?
Acetic acid would certainly make it easier to distill out the HI, and if acetic acid/HI could be used as is... you couldn't get much simpler and neater really...
