High resolution mass spectrometric and high-field nuclear magnetic resonance spectroscopic studies of the herbicide propanil, its N-oxidative decomposition products and related compounds.

Abstract

A number of compounds associated with dichloroaniline-based herbicides were examined by high resolution mass spectrometry and high-field nuclear magnetic resonance spectroscopy. These compounds included the herbicide propanil (N-propionyl-3,4-dichloroaniline) and the related compound N-acetyl-3,4-dichloroaniline. Several possible oxidative metabolic products, including N-hydroxy-3,4-dichloroaniline, nitroso-3,4-dichlorobenzene, N-hydroxy-N-propionyl-3,4-dichloroaniline and N-hydroxy-N-acetyl-3,4-dichloroaniline were also investigated. Mass spectral fragmentation schemes were proposed, based on exact mass measurements for fragment ions from these related compounds. The change in fragmentation behavior upon oxidation of the N-acyl compounds to N-hydroxy-N-acyl derivatives was found to be quite significant. The N-hydroxy-substituted compounds showed extensive fragmentation while the analogous non-hydroxylated compounds and nitroso-3,4-dichlorobenzene showed little fragmentation. Line broadening detected in several of the high-field nuclear magnetic resonance spectra was attributed to cis-trans isomerization. The highly toxic 3,3',4,4'-tetrachloroazobenzene and 3,3',4,4'-tetrachloroazoxybenzene were also examined by high resolution mass spectrometry.