数種の脂肪酸による2-メチルピリジンのH-D交換反応

抄録

Hydrogen deuterium exchange reaction of 2-methylpyridine has been studied by using several fatty acids as catalysts. The reaction was carried out in a sealed pyrex tube at 120°C, and the contents of the products were determined by mass spectrometry. Reaction of 2--methylpyridine with monodeuteroacetic acid (1 : 1, mol/mol) arrived at a equibrium (d₀_??_d₁_??_d₂_??_d₃) in 2 hr (d₀ 41%, d₁ 42%, d₂ 15%, d₃ 2%). No exchange was observed for the reaction of pyridine with monodeuteroacetic acid. The conversion-time curves of typical series reactions (d₀ → d₁→ d₂ → d₃) were obtained for the fatty acid catalyzed exchange in deuterium oxide. The effect of the fatty acid RCO₂H (substrate fatty acid : D₂O=1 : 0.86 : 276, mol/mol/mol) on the conversion was in the order of R; C₁-C₃<C₄-C₁₀, where the reaction mixtures were homogeneous in the case of C₁-C₃ and were heterogeneous in the case of C₄-C₁₀. The effects of the initial concentration of the substrates and the catalysts (RCO₂H) on the total conversion were studied by using some fatty acids (R; C₂, C₄ and C₉) in deuterium oxide (for 2 hr). The total conversion of the substrate increases with increasing the concentration of the acids. The total conversion decreases in the case of R=C₉, but, increases in the case of R=C₂ with increasing the concentration of the substrate. In the case of reactions with low concentrations of the substrate, the reactivity was in the order of C₉>C₄>C₂, while with high concentrations, the reactivity was in the order of C₄>C₂C₉ and C₉>C₄>C₂ with high and low concentrations of the acids, respectively. A possible reaction mechanism was proposed and discussed.