THERMAL-DECOMPOSITION OF 1,2,3,4-THIATRIAZOLES - QUESTION OF THIOACYL AZIDE AND THIOACYLNITRENE INTERMEDIATES

The kinetics of decomposition of 5-phenyl-1, 2, 3, 4-thiatriazole to benzonitrile, sulfur, and nitrogen were investigated in bromobenzene at 52.2-61, 1 °C and found to be first order with Ea = 118.0 kJ·mol-1 and ΔS⧧ = 11.7 J-mol-1 K-1, A linear Hammett correlation was obtained with substituted phenylthiatriazoles (p ≈ 0). Kinetic isotope effects with 4-, 5N- and 2-15N-labeled phenylthiatriazole were observed to be ~4 and 0%, respectively. The effect of Lewis acids and of dipolarophiles on the decomposition was investigated. The overall observations are interpreted to imply a three-step mechanism via (E)-thiobenzoyl azide. There is no evidence for a thiobenzoylnitrene intermediate. Phenyl isothiocyanate, which is formed from phenylthiatriazole above ~100 °C, is suggested to result from a concerted rearrangement from (Z)-thiobenzoyl azide. © 1978, American Chemical Society. All rights reserved.