Spectrometric Characterization of Metribuzin and its Metabolites

Abstract

Metribuzin and its three major plant metabolites have been characterized by ultraviolet, infrared, and proton NMR spectroscopy and mass spectrometry. The reported structures for these compounds have been confirmed, except that deaminated Metribuzin (DA) exists mainly in the enol form rather than the keto form usually reported. Evidence is presented concerning the most probable sites of protonation during titration of these compounds. Whereas diketo Metribuzin (DK) does undergo protonation of the amino group, Metribuzin itself apparently does not. Keto/enol tautomerism as a function of pH greatly complicates interpretation of the spectra. Metribuzin appears to form a poorly soluble, hydrogen-bonded dimer (or polymer) when titrated from basic to acidic pH.