Kinetics and mechanism of izomerization of N-alkoxycarbonyl-5-aroxytetrazoles

The kinetics and mechanism of the N-2-N-1-isomerization of 2-methoxycarbonyl-5-(p-X-phenoxy)tetrazoles (X = H, CH3, NHCOCH3, Cl, Br, NO,) were studied by H-1 NMR spectroscopy in a DMSO-d(6)-CDCl3 mixture (25: 75). The rate of isomerization of the N-2-isomer into N-1-isomer fit the first-order equation (after three half-conversion periods). The isomerization is accompanied by hydrolysis and decarboxylation. The Hammett plot of ln(k(x)/k(H)) for the isomerization showed a good correlation with sigma(-) values (p(-) = 1.33, r = 0.965). A poor correlation with sigma values was obtained. The kinetic data, the effect of solvent polarity, the substituent effects, and the results of AMI quantum-chemical calculations suggest an ionic mechanism of the isomerization in polar solvents and a concerted mechanism in nonpolar solvents.