21367-45-3Relevant articles and documents
Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects
Cabelkova-Taguchi, Lubomira M.,Warkentin, John
, p. 100 - 105 (2007/10/02)
A series of 5,5-dimethyl-4-Δ1-1,2,4-triazolin-3-ones (Ar=C6H5, p-C6H4CH3, p-C6H40CH3,p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina.The triazolines decompose in solution to N2,CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148-200 deg C.Average activation parameters are ΔH*=35 kcal*mol-1 and ΔS*=8 cal*K-1*mol-1.Substituent effects are correlated through Σ-constants but the thermolyses are relatively insensitive to substituents, with p=-0.17 at 172.5 deg C.Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation.Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.
