| Abstract
| - Kinetic measurements for the degradation of 4-hydroxyphenylpentazole (2a) and its salt 2b-NBu4in CD3OD and in CD2Cl2 provided a set of activation parameters. The resulting free energies ofactivation in methanol (ΔG‡298 = 19.7 kcal/mol for 2a and ΔG‡298 = 20.6 kcal/mol for 2b-NBu4)were compared with previous results for the 4-chloro derivative, 2c, and collectively correlatedwith results of gas-phase calculations at the B3LYP/6-31+G(d,p) level of theory. This, and anotherlinear correlation of the seven computed ΔG‡298 values with the previously reported kinetic data ofUgi and Huisgen, gave the basis for the estimation of the stability of pentazole anion (1) and itsderivatives in solutions. Thus, N5(−) is predicted to have t1/2 = 2.2 d, while the half-lifetime forHN5 is expected to be only about 10 min in methanol at 0 °C. Controlled ozonolysis of 2b-NBu4followed by 1H and 15N NMR spectroscopy shows a preferential destruction of the N5 ring, whichexcludes it from possible methods for preparation of the parent pentazole.
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