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 ).