Laser photolysis study on the reaction of nitrate radical with tributylphosphate and its analogues—comparison with sulfate radical

Abstract

Time resolved laser photolysis was carried out to study the reaction of NO₃˙ radical toward a series of organic phosphates (tributylphosphate (TBP) and its analogues) with different length of side alkyl groups such as CH₃, C₂H₅, C₃H₇, CH(CH₃)₂ and C₄H₉ in water, acetonitrile, and the mixtures of water and acetonitrile, respectively. For comparison, a similar investigation on SO₄˙⁻ radical was also conducted. The oxidation reaction of NO₃˙ and SO₄˙⁻ radical with the phosphates was attributed to mainly an H-abstract reaction. The kinetics study shows that the rate constants of the reaction between the two radicals and phosphates increase remarkably with increasing of the length of the alkyl groups, e.g. in the case of NO₃˙ radical in acetonitrile, the rate constant increases by almost 4 orders of magnitude from TMP (–CH₃) to TBP (–C₄H₉). The composition of the solvent also greatly affects the reactivity but it exhibits an opposite effect of the two radicals, the rate constant of NO₃˙ increases with the mole fraction of acetonitrile while that of SO₄˙⁻ decreases. The present study would be helpful for understanding the mechanism of deterioration of TBP in the Purex process.