A kinetic study of the high temperature rearrangement of 4-ethyl-3,5-diphenyl-4H-1,2,4-triazole

The kinetics of the thermal rearrangement 4-ethyl-3,5-diphenyl-4H-1,2,4-tia zoles, 1, to the corresponding 1-ethyl-3,5-diphenyl-1-alkyl-1H-1,2,4-triazo les, 2, was studied in 15-Crown-5 and octadecane at 330 degreesC. The react ion was very slow in octadecane but proceed well in 15-Crown-5. The reactio n order for the reaction was not constant but changed from an initial secon d order rate law towards a first order rate law as the reaction progressed. This was confirmed by the concentration dependent reaction order, n(c), wh ich was larger than the time dependent rate law, n(t). The rationale for th e observation was, that at high substrate concentrations the reaction order was second order while at lower concentrations a competing solvent assiste d reaction plays an increasing important role. The data were in agreement w ith a mechanism in which the neutral 4-alkyl-triazoles in an intermolecular nucleophilic displacement reaction form a triazolium triazolate, which in a subsequent nucleophilic reaction gives the observed product.