GAS-CHROMATOGRAPHIC ANALYSIS OF REDUCTION PRODUCTS OF PARAQUAT, DIQUAT AND THE RELATED-COMPOUNDS - REDUCTIVE CLEAVAGE OF N-ALKYLPYRIDINIUM DERIVATIVES WITH NABH4-NICL2 REDUCTION SYSTEM

The structures of by-products, observed as weak side peaks on the chro matogram by gas chromatographic analysis, were estimated by gas chroma tography (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 c onfirm the estimated structures of the by-products described above, a preparative scale reduction was carried out on I and II, and we succee ded in the isolation and purification of III and IV by thin-layer chro matography. The structures of both III and IV were supported on the ba sis of H-1- and C-13-nuclear magnetic resonance spectra. In addition, for the purpose of discussing the regularity in this reductive cleavag e reaction, the related compounds such as 1,4-dimethylpyridinium iodid e (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 dieth yl derivative of I, were reduced with NaBH4 (or NaBD4)-NiCl2. We eluci dated by GC-MS analysis that the reductive cleavage reaction at CN bon d in V, VII and VIII except for VI occurred as side reaction. In the p revious paper, we reported that a correlation between the yield of the by-product of I and amounts of reductants NaBH4 and NiCl2 in water wa s 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.