In situ photolysis-electron spin resonance study of some reactions of phosphate radicals
Free radical intermediates formed in the reaction of phosphate radicals (PO/sub 4//sup 2 -/ or its protonated forms, HPO/sub 4//sup -/ and H/sub 2/PO/sub 4/) with a number of fundamental organic and inorganic compounds have been studied by the in situ photolysis-steady state ESR method. The phosphate radicals were generated effectively by the photolysis of peroxodiphosphate (P/sub 2/O/sub 8//sup 4 -/) in aqueous solutions. Though the phosphate radical itself could not be detected directly, the ESR spectra of the phosphate radical adducts to fumaric and maleic acids and also the aci-anion of nitromethane were observed successfully. The pK/sub a/ value for the proton dissociation in the phosphate group of the adduct to fumaric and maleic acids, /sup -/OOCCH(OPO/sub 3/H/sup -/)CHCOO/sup -/, has been determined to be 6.7. The reactions of phosphate radicals are rather similar to those of the related active species SO/sub 4//sup -/, e.g., they give rise to hydroxyalkyl radicals from aliphatic alcohols, adduct radicals with unsaturated compounds, and inorganic radicals such as CO/sub 3/ from HCO/sub 3/ and PO/sub 3//sup 2 -/ from HPO/sub 3//sup 2 -/. However, there are notable differences in reactions with aliphatic and aromatic carboxylic acids. From saturated aliphatic mono- and dicarboxylic acids, ..cap alpha..-carbon radicals produced by hydrogen abstraction with phosphate radicals were predominantly detected in neutral aqueous solutions and phenyl-type radicals were not detected from aromatic carboxylic acids. On the contrary the resultant radicals by decarboxylation were mainly observed in SO/sub 4//sup -/ system. Clearly, direct oxidative electron transfer is not the predominant process in the reaction of the phosphate radical (HPO/sub 4//sup -/) with carboxylic acids.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 7282850
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 81:20
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
OXYGEN COMPOUNDS
PHOTOLYSIS
PHOSPHORUS COMPOUNDS
RADICALS
CHEMICAL REACTIONS
ACID PHOSPHATES
ANIONS
ELECTRON SPIN RESONANCE
PHOSPHATES
CHARGED PARTICLES
DECOMPOSITION
IONS
MAGNETIC RESONANCE
PHOTOCHEMICAL REACTIONS
RESONANCE
400500* - Photochemistry