Peroxodiphosphoric acid

H3B03 orthoboric acid (or boric acid) H4P2O3 peroxodiphosphoric acid... 

Pure peroxodiphosphoric acid [13825-81 -5] has not been obtained, but its properties ia aqueous solution are understood. As iadicated by... 

There are four ionizable hydrogen atoms on the corresponding peroxodiphosphoric acid, for which pifj = —0.3, P-A2 P- 3 — -2, and... 

P-A4 = 7.7 (47). The rates of hydrolysis of the peroxodiphosphate ion are dependent on both pH and temperature, eg, as the hydrogen ion concentration iacreases, the rate iacreases (48). Peroxodiphosphoric acid hydroly2es to peroxomonophosphoric acid according to the foUowiag equation ... 

However, the peroxomonophosphate ion decomposes relatively rapidly ia aqueous solution. A mixture of peroxodiphosphoric and peroxomonophoshoric acids can be produced by treatiag a cold phosphoric acid solution with elemental fluorine (qv) (49). Peroxodiphosphoric acid is not produced commercially. Ammonium, lithium, sodium, potassium, mbidium, cesium, barium, 2iac, lead, and silver salts have all been reported. The crystal stmctures of the ammonium, lithium, sodium, and potassium compounds, which crysta11i2e with varyiag numbers of water molecules, have been determined (50). 

Peroxomonophosphoric acid and peroxodiphosphoric acid have both been used to oxidize sulphoxides to sulphones. 

Peroxodiphosphoric acid (PDPA) may also be used to convert sulphoxides to sulphones in good yields. An initial study of this reaction80 concluded that the mechanism was a free radical process, involving the reaction of a hydroxyl radical with the sulphoxide as shown in equation (26). This was later claimed to be incorrect the reaction actually occurs by the initial decomposition of PDPA to PMPA which then reacts as described above81. 

The less protonated species are relatively insignificant. Crutchfield" " usedan expression which did not include the first term in (3) and consequently achieved best fit with different values of the rate coefficients to those reported by Goh et al. . The equilibrium constants, K, K2, for peroxodiphosphoric acid have been estimated as 2.0 and 0.3 by consideration of the corresponding values for hypo-phosphoric and pyrophosphoric acids. The values of the rate coefficients and the mechanistic interpretation of the kinetics are thus somewhat uncertain. Some data in terms of (3) has been published (Table 20). The activation energies for the overall process vary" from 18.3 (pH 0) to 28 kcal.mole (pH 3). 

Reaction of peroxodiphosphoric acid with fluoride ion appears to be established. 

Peroxoacids, in which -O- is replaced by -0 0-, are similarly distinguished by the prefix peroxo- (peroxy-or simply per- have frequently been used in the past), as, for example, in HNO4 peroxonitric acid and K2SO5 potassium peroxosulphate, HO 0 1 0 peroxonitrous acid, and H4P2O8 peroxodiphosphoric acid. 

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