Characterizing the Sethoxydim-Bentazon Interaction with Proton Nuclear Magnetic Resonance Spectrometry

Abstract

The antagonistic effect of Na-bentazon on sethoxydim absorption and herbicidal activity has been documented. The addition of ammonium sulfate (AMS) with a surfactant overcomes the observed loss of sethoxydim activity. Nuclear Magnetic Resonance (NMR) was used to study the chemical effects of commercially formulated Na-bentazon, NaCl, NaHCO3, Na-bentazon plus AMS, and NaHCO3plus AMS on commercially formulated sethoxydim. Technical grade Li-sethoxydim and sethoxydim were analyzed and1H-NMR spectra were used as comparative standards. Data indicate an association of Na+from Na-bentazon, NaHCO3, and NaCl with the sethoxydim molecule. NH4+from AMS appears to associate spatially with sethoxydim but does not exert the same electronic effect on the sethoxydim ring protons as observed with Na+or Li+. The addition of AMS to sethoxydim plus Na-bentazon or NaHCO3treatments prevents the complexation of Na+with the sethoxydim molecule. The data support the hypothesis that the observed Na-bentazon antagonism and ammonium sulfate reversal of antagonism are chemically based.