Kinetics of the Azo-Diels-Alder Reaction of Naphthalene with 4-Phenyl-1,2,4-triazoline-3,5-dione in Solution and Solid Phase

The kinetics of the azo-Diels-Alder reaction of 4-phenyl-1,2,4-triazoline-3,5-dione (1) with naphthalene (2) in solution and solid phase without a solvent was studied by manually grinding the reactants with a pestle and mortar. It was found that the 1 + 2 mechanochemical reaction proceeds with an initial induction period, which decreases from 30 to 0 min as the temperature increases from 295 to 314 K. The 1 + 2 solvothermal reaction proceeds without an initial induction period. The duration of the period corresponding to the 1 + 2 chemical reaction under mechanochemical activation conditions is constant (10 min) in the temperature range of 295–314 K. A correlation was found between the duration of the induction period of the 1 + 2 mechanochemical reaction and the rate constant of the 1 + 2 solvothermal reaction in the temperature range of 295–314 K. It was found that the maximum conversion of 2 during the 1 + 2 mechanochemical reaction is constant within the measurement errors in the temperature range of 295–314 K. This behavior of the 1 + 2 reaction under mechanochemical conditions differs sharply from the behavior of the 1 + 2 reaction under solvothermal conditions, in which the maximum conversion of 2 decreases with increasing temperature. The behavior of azo-Diels-Alder reactions between 1 and various polycyclic aromatic hydrocarbons (PAHs) in solution and in solid phase was compared. A correlation was found between the maximum yield of 1-PAHs adducts in the solid phase and the enthalpy of these reactions in solution. For reactions of 1 with anthracene derivatives, a correlation was observed between the duration of the induction period in the solid phase and the rate constant in solution. The point corresponding to the 1 + 2 reaction deviates from this correlation. The results suggest that the duration of the induction period for mechanochemical azo-Diels-Alder reactions depends not only on the reactivity of the reactants but also on their crystal lattice energy.