The Kinetics of Phosphate Radical Ions in Aqueous Solutions (a)
Janina A. Rosso, Mónica C. Gonzalezb and Daniel O. Mártirec
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas,
Universidad Nacional de La Plata, Casilla de Correo 16, Sucursal 4, (1900) La Plata, ARGENTINA.

FAX: --54 21 25 4642; e-mail: ___________________________________________________________________ a Manuscript in preparation.
b Research member of Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina).
c Research member of Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (Argentina).

Keywords: Phosphate radical ions, flash-photolysis, oxygen adducts.


Phosphate radicals exist in three acid-base forms (PO4H2., PO4H.-, PO4.2-) related by fast equilibria (eq. (1)). These radicals were reported to react with organic and inorganic substrates [1] either by hydrogen abstraction or by electron transfer with different efficiency.

Huber and Hayon [2a] studied the decay kinetics of phosphate radicals generated by VUV photolysis of HPO42- and H2PO4. (e.g. reaction (2)).

These authors observed a second order decay of phosphate radicals in Ar-saturated solutions and a first-order decay kinetics in the presence of molecular oxygen. These results were interpreted in terms of the formation of oxygen adducts with HPO4.- or H2PO4. [2a]. In all other more recent literature reports, phosphate radicals were generated in the absence of molecular oxygen [2b].
Waste-water oxidative procedures based on the generation of HO. or SO4.- [3] radicals initiating organic substrates oxidation, may also form phosphate radicals (PO4H2., PO4H.-, PO4.2-) from the reaction of HO./ SO4.- with phosphate ions contained in high concentrations in the water matrix [1, 4]. However, the information reported in the literature on the reactivity of the phosphate radicals is scarce [1, 5].
We here studied the decay kinetics of PO4H2., PO4H.-, PO4.2- generated by photolysis of peroxodiphosphate ions (reaction (4)) in N2 and O2-saturated solutions, both in the presence and absence of added substrates.