FACTORS AFFECTING THE RATES OF THERMAL-DECOMPOSITION OF AZIDOTHIOPHENES

The thermolysis rate of 4-methoxy-1-azidobenzene reveals that the methoxy group increases the rate much less than the endocyclic sulfur does in 3-azidothiophene. With 3-azidothiophene, the neighbouring groups 2-acetyl and 2-nitro enhanced the rate in decalin solution only 5- and 17-fold, respectively, whereas in azidobenzene the corresponding enhancements are 413 and 1060. It is argued that the preferred electron distribution in the transition state for decomposition of 3-azidothiophene is not consistent with that required for effective neighbouring group participation. 2-Cyano and 2-methoxycarbonyl substituents, which are not known as effective neighbouring groups in thermal decompositions of azides, have very little effect on the rate for 3-azidothiophene.