Interaction of Electron-Deficient 1,2,4-Triazoline-3,5-diones with Electron-Rich Polyalkoxybenzenes

Article abstract of DOI:10.1021/jo00158a025

4-Substituted-1,2,4-triazoline-3,5-diones have been found to form charge-transfer complexes with 1,3,5-trimethoxybenzene, 1,3-dimethoxybenzene, and 1,4-dimethoxybenzene but not with anisole.In the cases of 1,3,5-trimethoxybenzene and 1,3-dimethoxybenzene a reaction occurs to give aromatic substitution; the relative rates are 1,3,5-trimethoxybenzene >1,3-dimethoxybenzene >1,4-dimethoxybenzene.The rate of reaction of 4-butyl-1,2,4-triazoline-3,5-dione (n-BuTAD) with 1,3,5-trimethoxybenzene (TMB) increases with decreasing temperature to give apparent activation parameters: ΔH^* = -5.9 kcal/mol, ΔS^* = -78 cal deg^-1 mol^-1.The rate is also dependent on the length of time that solutions of the n-BuTAD are exposed to ambient light, suggesting involvement of the urazolyl radical.It is suggested that the overall rate expression is - = k₁K_eq(n-BuTAD)(TMB)(Ur.), where (Ur.) is the urazolyl radical concentration, K_eq is the equilibrium constant for charge-transfer complex formation, and k₁ is the rate constant for attack of Ur. on the charge-transfer complex.