A NEW METHOD FOR MEASURING CARBONATE RADICAL REACTIVITY TOWARD PESTICIDES

摘要

The carbonate radical is produced from the scavenging of the hydroxyl radical by carbonate/bicarbonate and is strongly electrophilic toward electron-rich compounds such as aromatic amine and sulfur-containing compounds. Carbonate radical reactivity (CO_3~(.-) ) was measured by setting up a competition between a chemical of known reactivity and a compound with unknown reactivity toward CO_3~(.-). The carbonate radical was produced using a novel method whereby KOONO (potassium peroxonitrite) was dissolved into 0.0l NaHCO_3 solution initially producing a HO', which was rapidly scavenged by HCO_3, yielding CO_3~(.-).CO_3~(.-) production was monitored using a stopped-flow spectrometer at the absorption band for CO_3~(.-) of 600 nm. Results using this competition kinetic method indicated the second-order rate constants for substituted anilines corresponded to reference values with a relative error less than l0. Using σ_(para)~+ values, the rate constants of substituted anilines at pH 9.0 correlated well (R~2 = 0.98) with the Hammett equation yielding p = -0.89. TO measure the reactivity of pesticides toward the carbonate radical, p-nitroaniline (PNA) was selected as the standard competitor. Of the nine pesticides tested, fenthion was the most reactive, followed by phorate, with rate constants above 10~7/M/s. Fluometuron and atrazine were of intermediate reactivity, and methyl parathion was one of the least reactive.