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M. S. Akhlaq N. Grossmann E. Pasbrig E. Fanghnel 《Advanced Synthesis \u0026amp; Catalysis》1987,329(2):217-223
On the Coupling of 4-Substituted 2-Pyrazoline-5-ones with Quinone Diimine Cations; Detection of Isokinetic Relations The temperature dependence of the rate constant kK of the coupling reaction between pyrazoline-5-ones 1a – i and quinone diimine cations 2a , b is determined in dependence of the substituents at the coupling position (R3: H, NN Ar, CHAr–pyrazoline-5-one). The activation enthalpies are between 7 and 60 kJ mol−1 and the activation entropies between −132 and −19 J mol−1 K−1. An isokinetic relation with β = 106°C is found and a rate determining combination of the carbanions of 1a – i with 2a , b is proposed. Contrary to this, the 2-pyrazolin-5-ones 1j – l , n (R3: S CNH2NR) obey an isokinetic relation with β = −45°C. Taking into consideration the activation parameters, the low dependence of kK on the ionic strength, and the decrease of kK with the increase of the pK values of the couplers, a rate determining splitting off of R3 is assumed. 相似文献
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