THEORETICAL-ANALYSIS OF ACETYLTRIAZENE AND THE MECHANISTIC IMPLICATIONS OF ITS REACTION WITH ACID

Theoretical calculations have been carried out on the protonation of 3-acetyltriazene in order to provide insight into the mechanism of the acid-catalyzed decomposition of acyltriazenes. We have previously reported the results of calculations on a series of alkyltriazenes. Ab initio RHF calculations were carried out at the 3-21G level to determine the optimized SCF energies and geometries of the neutral molecule and some site-specific protonated species. This allowed an estimate of the proton affinity at each site. Experimental studies on alkyltriazenes indicated that initial protonation at the N3 site was critical in the acid catalysis mechanism, even though the calculated proton affinities indicated that N1 was a more basic site. In the case of the acyltriazenes, the calculations showed that the proton affinity at N3 was much lower than that at N1 or at the carbonyl oxygens. The geometrical changes produced by protonations at the various sites indicated that the N2-N3 bond shows a propensity for cleavage upon protonation at either N3 or at the carbonyl oxygen. These results suggest that acid-catalyzed decomposition of acetyltriazene would involve the breakage of the N2-N3 bond, rather than the hydrolysis of the acyl group. Subsequent experimental data supported this conclusion. A linear scaling method was applied to the geometric and energetic results from the semiempirical AM1 code to predict the results of the 3-21G calculations with a surprising degree of success. A predictor function to allow AM1 geometries and proton affinities to provide a good estimate of 3-21G results is given, and the limitations are discussed.