Mechanisms of thermal decomposition of 1-[2,2-bis(methoxy-NNO-azoxy)ethyl]pyrazole

The previously proposed alternative mechanisms of thermal decomposition of 1-[2,2-bis(methoxy-NNO-azoxy)ethyl]pyrazole were verified by quantum chemical calculations. The main ones are two competitive channels: 1) the transfer of one of the two β-H atoms to the O(1) atom via a 5-membered transition state with an activation enthalpy of ∼160 kJ mol⁻¹ and MeOH and N₂O as the main volatile products; 2) the transfer of an H atom to the pyrazole ring with subsequent elimination of pyrazole and an activation enthalpy of ∼180 kJ mol⁻¹. An alternative mechanism via a zwitterionic intermediate with a three-center hydrogen bond and an activation enthalpy of 263 kJ mol⁻¹ cannot compete with the main channels in the gas phase. However, taking into account a number of factors of thermolysis in the liquid phase and a relatively low barrier of conversion of the zwitterionic intermediate (145 kJ mol⁻¹), the alternative mechanism can make a considerable contribution to the overall process, with its contribution being determined by the stationary concentration of the zwitterionic intermediate.