Behavior of Hydrochlorides and Methiodides of N-Substituted 4-Piperidones in Methanol

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The behavior of hydrochlorides and methiodides of several N-substituted 4-piperidones in CH_3OH has been studied by ^<13>C nuclear magnetic resonance (NMR) spectroscopy. All the piperidone salts studied were observed to exist as their hemiacetal form at room temperature, in contrast to the case of free piperidones, where an equilibrium mixture of ketone and hemiacetal was obtained. This difference could be accounted for by the effect of the positive charge on nitrogen, which increases the instability of the salt of the keto-form. Acetal formation was observed only in more acidic solutions. The corresponding O- and S-analogs were also examined in CH_3OH, and it was found that they are converted readily to the acetals in the presence of trace amounts of acid. The reaction mechanisms of these compounds and piperidone salts are compared and discussed. ^<13>C NMR techniques were found to be useful for studying the equilibrium system containing both hemiacetal and acetal.
公益社団法人日本薬学会の論文
1980-12-25