Reactivity of neonicotinoid insecticides with carbonate radicals

Abstract

The reaction of three chloronicotinoid insecticides, namely Imidacloprid (IMD), Thiacloprid (THIA) and Acetamiprid (ACT), with carbonate radicals (CO3 center dot-) was investigated. The second order rate constants (4 +/- 1) x 10(6), (2.8 +/- 0.5) x 10(5), and (1.5 +/- 1) x 10(5) M-1 s(-1) were determined for IMD, THIA and ACT, respectively. The absorption spectra of the organic intermediates formed after CO3 center dot- is approximately equal to attack to IMD is in line with those reported for alpha-aminoalkyl radicals. A reaction mechanism involving an initial charge transfer from the amidine nitrogen of the insecticides to CO3 center dot- is proposed and further supported by the identified reaction products. The pyridine moiety of the insecticides remains unaffected until nicotinic acid is formed. CO3 center dot- radical reactivity towards IMD, ACT, and THIA is low compared to that of HO center dot radicals, excited triplet states, and O-1(2), and is therefore little effective in depleting neonicotinoid insecticides. (C) 2012 Elsevier Ltd. All rights reserved.