Gas liquid chromatography-mas spectrometry of paraquat and diquat reduction products. A reductive cleavage of paraquat and diquat by NaBH4 in the presence of a transition metal salt (Ni2+).

Abstract

When herbicide preparations paraquat(I) and diquat(II), based on N-alkylbipyridylium derivatives, were analyzed by gas liquid chromatography (GLC) with sodium borohydride (NaBH4)-nickel(II) chloride (NiCl2) reduction, the chromatograms showed minor side peaks from slight amounts of by-products appearing in front of the main peaks, arising from the respective perhydrogenated products of I or II.Reductive cleavage of a C-N bond within each pyridine ring of I or II was suggested in view of the production of trifluoroacetic acid derivatives prepared from these by-products.The by-products, whose structures were elucidated by GLC-mass spectrometry, were consequently presumed to be p-(N-methylaminopent-3'-yl)-N-methylpiperidine, arising from I, or 1 butyl-2-aza-perhydroquinolizine, arising from II.Correlation was also observed between the amounts of NaBH4 and NiCl2 and the production of by-products; the less NaBH4 and the more NiCl2 in a given volume of water, the greater the increase in side reaction products.The side peaks could not be observed on the gas-chromatogram when perhydrogenated products prepared separately from I and II were treated by NaBH4-NiCl2 reduction. The side peaks could be observed, however, when incomplete reduction products with one or two double bonds, obtained by reduction of I and II by NaBH4 alone, were reduced by NaBH4-NiCl2 reduction. It could therefore be presumed that this reductive cleavage at a C-N bond occurred, the intermediate state being the complex between nickel and incomplete reduction products with one or two remaining double bonds in the pyridine ring.