1979 Volume 28 Issue 5 Pages 295-299
Deuterated piperidines with various deuterium contents were obtained by a catalytic reduction of pyridine with deuterium gas (99.0 atom %) on platinum oxide and of pyridine-d5 (99.0 atom%) with hydrogen gas or deuterium gas. Mass spectrometric analysis of the deuterated piperidines revealed marked scrambling of deuterium label. After methylation of an equal amount of unlabeled piperidine and the deuterated piperidine with diazomethane, the mixture was injected to gas chromatograph/mass spectrometer. Selected ion monitoring was performed by focussing to the m/z values of parent ions of N-methylpiperidine and deuterated N-methylpiperidine to obtain mass fragmentograms. An isotope effect was observed on the gas chromatographic behavior of deuterio and protio variants. Using a 1.5% OV-1 column, the protio variant was eluted faster than the deuterio variant. On the other hand, the latter was eluted faster than the former on a 5% dinonylphthalate column. In both cases, the difference in the retention time between the deuterio and the protio variants was nearly proportional to the number of deuterium atoms in a piperidine molecule.
These results suggest that, in a stable isotope tracer technique, it is necessary to consider the scrambing of deuterium label in the labeled compounds obtained by a catalytic reduction. Moreover, it should be noted that ion peak intensities on the mass spectrum measured at one point on the gas chromatogram may give an erroneous ratios of unlabeled and labeled compounds.
