NMR Study of the Influence of pH on the Persistence of Some Neonicotinoids in Water  

Valéria Guzsvány, János Csanádi, Ferenc Gaál*

Department of Chemistry, Faculty of Sciences, Trg D. Obradoviĉa 3,
21000 Novi Sad, Serbia and Montenegro
e-mail: gaal@ih.ns.ac.yu (F. F. Gaál)


The influence of the pH on the persistence of four neonicotinoid insecticides: imidacloprid, thiamethoxam, acetamiprid and thiacloprid, was studied by 1H NMR spectrometry at different pH values of Britton-Robinson buffers (4.0, 7.0 and 9.0) at a constant temeprature. Thiamethoxam and imidacloprid, having an identical nitro-guanidine functional group, exhibited low persistence in alkaline media, as their degradation started already after three and five days, respectively. On the other hand, at pH 4.0 and 7.0 they remained unaffected for several months. In contrast to them, thiacloprid and acetamiprid, the compounds with a cyanoimine functional group, were less persistent in acidic solution. In alkaline media, they were stable for about 30 days. The proportion of hydrolyzed pesticide was calculated from the 1H NMR spectra by comparing the integrals of compound signals with the signal of acetate standard.

Key words: imidacloprid, thiamethoxam, acetamiprid, thiacloprid, persistence, 1H NMR-study