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

When N-alkylpyridinium derivatives were reduced with sodium borohydrid e-nickel (II) chloride reduction system, reductive cleavage occurred a t the C-N bond in the pyridine ring of N-alkylpyridinium derivatives t o give a small amount of reductive cleavage product along with the maj or perhydrogenated product. It was presumed in the previous report tha t this reductive cleavage in the pyridine ring proceeded through a com plex of nickel ion and 1,2,3,6-tetrahydropyridine derivatives produced with NaBH4 alone reduction. The abundances of these reductive cleavag e products arising from N-alkylpyridinium derivatives, i.e., paraquat, diquat and so on, are capable of giving a bad effect on the accuracy of gas chromatographic analysis. For the purpose of inhibition of the reductive cleavage in this reduction system, a suitable catalyst was e xamined. In addition, we pursued whether borane-1,2,3,6-tetrahydropyri dine derivative complexes arose from N-alkylpyridinium derivatives by NaBH4 alone reduction or not, and whether these borane-amine complexes were the precursors of reductive cleavage products or not. N-Alkyl-1, 2,3,6-tetrahydropyridine derivatives (III-I, IV-I, VI-I, VII-I and VII I-I) and the corresponding borane-amine complexes (III-II, IV-II, VI-I I, VII-II, and VIII-II) were synthesized by NaBH4 reduction in aqueous solution of N-alkylpyridinium salts, i.e. I, II, 1,4-dimethylpyridini um iodide (III), 1-dodecylpyridinium chloride (IV), 1,1'-diethyl-4,4'- dipyridinium dichloride (V), 1-methyl-4-phenylpyridinium iodide (VI), 1-n-propylpyridinium iodide (VII) and 1-n-butylpyridinium iodide (VIII ). The structure of the borane-amine complexes were proved by the Mass spectrometry and H-1- and C-13-NMR analysis. The NiCl2-NaBH4 reductio n of the borane-amine complexes gave the perhydrogenated products alon e, but not reductive cleavage products. In conclusion, it was recogniz ed that the precursors of reductive cleavage products were not borane- amine complexes, but 1,2,3,6-tetrahydropyridine. Furthermore, it was f ound the reductive cleavage at the C-N bond in the pyridine ring of th ese 1,2,3,6-tetrahydropyridine derivatives was hindered by applying Am berlite-Ni2B, NaBH4 reduction system.