Isohypophosphoric acid

There has been much confusion over the structure of these compounds but their diamagnetism has long ruled out a monomeric formulation, H2PO3. In fact, as shown in Table 12.7, isomeric forms are known (a) hypophosphoric acid and hypophosphates in which both P atoms are identical and there is a direct P-P bond (h) isohypophosphoric acid and isohypophos-phates in which 1 P has a direct P-H bond... 

Tbe presence of P-H groups amongst the products of these reactions was one of the earlier sources of confusion in the structures of hypophosphorie and isohypophosphoric acids. 

The structure of isohypophosphoric acid and its salts can be deduced from nmr which shows the presence of 2 different 4-coordinate P atoms, the absence of a P-P bond and the presence of a P-H group (also confirmed by Raman spectroscopy). It is made by the careful hydrolysis of PCI3 with the stoichiometric amounts of phosphoric acid and water at 50° ... 

Isohypophosphoric acid (3/P-0-5/P acid) can be prepared by heating a mixture of phosphorous and phosphoric acids under appropriate conditions (5.249). Isohypophosphoric acid and its salts are readily hydrolysed (reverse of (5.244). The trisodium salt can be prepared by reacting sodium diphosphite and sodium orthophosphate (5.250), and it is stable in the solid or in neutral solution. 

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