Zur Umkupplung von 4-Arylazo-2-pyrazolin-5-onen mit p-Chinondiiminkationen

Recoupling of 4-Arylazo-2-pyrazoline-5-ones with p-Quinonediimine Cations

4-Arylazo-2-pyrazoline-5-ones (1a–j) readily undergo coupling reaction with p-quinonediimine cations (2a, b) to form azomethin dyes (3a, b). The dependence of the rate constants k_K of the dye formation on the substituents of 1a–j as well as on the ionic strength show that the rate-determining step of the coupling reaction is the formation of the intermediate 4 in a bimolecular reaction between the carbanions of 1a–j and p-quinonediimine (2a, b).

It became evident that the benzenediazoniumion (5a–j) is eliminated in the reaction of 4 to 3a, b. Under the coupling conditions used, substituted benzene is formed in the reduction reaction of 5a, b by the p-phenylendiamine (7a, b) or by the leuco dye (6a, b).