Abstract
The kinetics of the thermal rearrangement 4‐ethyl‐3,5‐diphenyl‐4__H__‐1,2,4‐triazoles, 1, to the corresponding 1‐ethyl‐3,5‐diphenyl‐1‐alkyl‐1__H__‐1,2,4‐triazoles, 2, was studied in 15‐Crown‐5 and octadecane at 330 °C. The reaction was very slow in octadecane but proceed well in 15‐Crown‐5. The reaction order for the reaction was not constant but changed from an initial second order rate law towards a first order rate law as the reaction progressed. This was confirmed by the concentration dependent reaction order, n~c~, which was larger than the time dependent rate law, n~t~. The rationale for the observation was, that at high substrate concentrations the reaction order was second order while at lower concentrations a competing solvent assisted reaction plays an increasing important role. The data were in agreement with 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.