1,3-Dialkyltriazenes: Tautomeric Equilibria and Rates and Products of Decomposition

Article abstract of DOI:10.1021/jo00266a008

Unsymmetrical 1,3-dialkyltriazenes, RN=NNHR', exist as a tautomeric mixture because of rapid proton exchange between nitrogens 1 and 3.Hydronium ion catalyzed decomposition of these triazenes gives rise to a mixture of alkanediazonium ions, RN2⁺ and R'N2⁺, and the corresponding primary amines.The objective of this study was to determine the factors that influence partitioning between the two pathways originating from the two tautomers.A series of 1-alkyl-3-methyltriazenes, where the alkyl groups were ethyl, n-propyl, n-butyl, isopropyl, tert-butyl, and benzyl, were prepared.A new, and potentially less hazardous, preparation of low molecular weight alkyl azides was developed.The corresponding symmetrical 1,3-dialkyltriazenes were also prepared.The rates of decomposition in aqueous buffers were measured.The general kinetic behavior suggested that the overall mechanism was specific acid catalysis in glycine buffer, in keeping with previously published data on symmetrical dialkyltriazenes (J.Am.Chem.Soc. 1986, 108, 3726-3730).The products of the decomposition of unsymmetrical triazenes were determined quantitatively, with particular reference to the alcohols formed by hydrolysis of the diazonium ions, RN2⁺ and R'N2⁺.The tautomeric distributions of the unsymmetrical triazenes were determined by NMR in various solvents, and it was found that Lewis base solvents (methanol, THF, acetone) capable of forming a hydrogen bond to the triazene gave very similar distributions, which was markedly different from solvents such as dichloromethane or chloroform.For each triazene, the tautomer in which the larger alkyl group is located on nitrogen 1 was favored.It was assumed that the distribution in water was similar to that observed in methanol.The rates of tautomerization were measured by dynamic NMR methods.Quantitative analysis of the combined data indicated that the unsymmetrical triazenes obeyed the Curtin-Hammett principle.Both the rates of decomposition of the triazenes and the ratios of the products are a function of the rates of decomposition of the conjugate acids of the tautomers and the mole fraction and basicity of the individual tautomers.The analysis also provides a means of predicting the ratios of alkanediazonium ions derived from unsymmetrical triazenes.