chlorination of disodium pyro-H-phosphonate?
Phosphorous acid, H3PO3, is a misnomer; the molecule is diprotic HP(OH)2O, H-phosphonic acid, forming two sodium salts, HP(ONa)(OH)O "sodium hydrogen
H-phosphonate" and HP(ONa)2O "disodium H-phosphonate" aka "sodium phosphite. The latter salt, sodium phosphite, is a fungicide.
The former salt, sodium hydrogen H-phosphonate, can dehydrate to disodium pyro-H-phosphonate, HP(ONa)(O)OP(O)(ONa)H, where both hydrogen atoms are
bonded to phosphorus (not protic).
https://en.wikipedia.org/wiki/Phosphite#Salts_containing_H2P...
H-phosphonate esters and possibly salts can be oxidized by halogens to replace the hydrogen with chlorine, see e.g.:
http://pubs.acs.org/doi/abs/10.1021/ma970390i (I figure that Cl2 is probably strong enough to oxidize the salt in any case)
Normally, the direct oxidation of H-phosphonic acid or its salts would lead to elimination of HCl and formation of a metaphosphate, but in the case of
Na2H2P2O5, there just isn't enough oxygen to form metaphosphate, so the reaction should look like this:
3 Na2H2P2O5 + 6 Cl2 >> 6 NaCl + H3P3O9 + P2O5 + 3HCl + POCl3
You can rearrange the sodium and hydrogen atoms a little, but you always end up with some P2O5 or POCl3 left over, which implies that this could be
used to synthesize those molecules. Remember that this reaction is apparently favorable:
P2O5 + 3 HCl >> H3PO4 + POCl3
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