パラコート, ジクワット及びその関連化合物に関する還元生成物のガスクロマトグラフィー : NaBH<SUB>4</SUB>-NiCl<SUB>2</SUB>系還元法によるN-アルキルピリジニウム化合物の還元的環開裂について

Abstract

The structures of by-products, observed as weak side peaks on the chromatogram by gas chromatographic analysis, were estimated by gas chromatography (GC)-mass spectrometry (MS) to be 4-(1-methylamino-pent-3'-yl)-1-methylpiperidine (III) arising from paraquat (I) and 1-butyl-2-aza-perhydroquinolidine (IV) arising from diquat (II). These by-products were resulted from the reductive cleavage at C-N bond in pyridine ring of I or II belonged to N-alkylbipyridinium derivatives. In order to confirm the estimated structures of the by-products described above, a preparative scale reduction was carried out on I and II, and we succeeded in the isolation and purification of III and IV by thin-layer chromatography. The structures of both III and IV were supported on the basis of 1H- and 13C-nuclear magnetic resonance spectra. In addition, for the purpose of discussing the regularity in this reductive cleavage reaction, the related compounds such as 1, 4-dimethylpyridinium iodide (V), 1-methyl-4-phenylpyridinium iodide (VI) and 1-dodecylpyridinium chloride (VII) replaced one in two pyridine rings by -CH3, -C6H5 and -H, and 1, 1'-diethyl-4, 4'-bipyridinium dichloride (VIII), i.e. a diethyl derivative of I, were reduced with NaBH4 (or NaBD4)-NiCl2. We elucidated by GC-MS analysis that the reductive cleavage reaction at C-N bond in V, VII and VIII except for VI occurred as side reaction. In the previous paper, we reported that a correlation between the yield of the by-product of I and amounts of reductants NaBH4 and NiCl2 in water was observed, and the yield of the by-product increased in the two-step (NaBH4 and NiCl2-NaBH4) reduction method rather than in the one-step (NiCl2-NaBH4) method.