Kinetics of the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione with β‐pinene and 2‐carene: Temperature, high pressure, and solvent effects

The data on temperature, solvent, and high hydrostatic pressure influence on the rate of the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione (1) with 2‐carene (2), and β‐pinene (4) have been obtained. Ene reactions 1+2 and 1+4 have high heat effects: ∆Hr‐n (1+2) −158.4, ∆Hr‐n(1+4) −159.2 kJ mol−1, 25°C, 1,2‐dichloroethane. The comparison of the activation volume (∆V≠(1+2) −29.9 cm3 mol−1, toluene; ∆V≠(1+4) −36.0 cm3 mol−1, ethyl acetate) and reaction volume values (∆Vr‐n(1+2) −24.0 cm3 mol−1, toluene; ∆Vr‐n(1+4) −30.4 cm3 mol−1, ethyl acetate) reveals more compact cyclic transition states in comparison with the acyclic reaction products 3 and 5. In the series of nine solvents, the reaction rate of 1+2 increases 260‐fold and 1+4 increases 200‐fold, respectively, but not due to the solvent polarity.