Functional phenoxazinone synthase models
2004; Elsevier BV; Volume: 215; Issue: 1-2 Linguagem: Inglês
10.1016/j.molcata.2004.01.006
ISSN1873-314X
AutoresTamás Horváth, József Kaizer, Gábor Speier,
Tópico(s)Chemical Reaction Mechanisms
ResumoSeveral copper compounds (CuCl, CuCl2, CuSO4, Cu(NO3)2, Cu(OAc)2, Cu(OCH3)2, and Cu(OCH3)(Cl)) have been used as catalysts for the oxidation of 2-aminophenol with dioxygen at 60 °C in DMF to 2-aminophenoxazine-3-one; a comparison of their activities was made through kinetic measurements. Stronger coordinating donor N-ligands (bpy, phen) accelerate the reaction rate remarkably and the amount of ligand influences the molecularity of the CuCl-catalyzed reaction. The overall second order rate equation was found at CuCl to phen ratio of 1:0 (k2/60°C=11.3±0.5×102 mol−3 l3 s−1), while the reaction is zero order with respect to 2-aminophenol concentration at a CuCl to phen ratio of 1:2 (k0/60°C=13.9±0.7×10−2 mol−3 l3 s−1). The kinetics of the CuCl(phen)-catalyzed reaction measured at 60 °C resulted in a rate equation with first order dependence on copper, dioxygen and 2-aminophenol. The rate constant, activation enthalpy, and entropy at 333.16 K are as follows: kobs=2.42±0.22 mol−2 dm6 s−1, Ea=25±1 kJ mol−1, ΔH‡=22±1 kJ mol−1 and ΔS‡=−170±13 J mol−1 K−1. The catalytic systems investigated can be viewed as functional models of the enzyme phenoxazinone synthase.
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