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N5 in Solution: Isotopic Labeling and Further Details of Its Synthesis by Phenyl Pentazole Reduction

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journal contribution
posted on 15.08.2017, 00:00 by Boris Bazanov, Uzi Geiger, Dan Grinstein, Shmuel Welner, Yehuda Haas
The cyclopentazolate anion, N5, has been researched extensively over the years and detected in the gas phase more than a decade ago, but was only recently measured in solution. The process whereby aryl pentazole reduction leads to the production of N5 is still not fully understood. Here, the production of N5 in solution was investigated using isotopic labeling techniques while implementing changes to the synthesis methodologies. 15N labeled phenyl pentazole produced appropriately labeled phenyl pentazole radical anions and N5 which, upon collision induced dissociation, produced the expected N3 signals. Changing to higher purity solvent and less coated Na metal allowed for a much more rapid pace, with experiments taking less time. However, the best yields were obtained with heavily coated metal and much longer reaction times. Utilization of a vacuum line and ultrapure solvents led to no products being detected, indicating the importance of a sodium passivation layer in this reaction and the possibility that sodium is too strong a reducer. These findings can lead to better production methods of N5 and also explain past failures in implementing aryl pentazole reduction techniques.