Tempo-initiated oxidation of o-phenylenediamine to 2,3-diaminophenazine

The oxidation reaction of o-phenylenediamine (PDA) to 2,3-diaminophenazine (DAP) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of PDA was followed by electronic spectroscopy and the rate constants were determined according to the rate law -dPDA]/dt = k _obsPDA]TEMPO]. The rate constant, activation enthalpy and entropy at 323 K are as follows: k _obs (dm³ mol^-1 s^-1) = (3.60±0.13) × 10^-6, E _a (kJ mol^-1) = 76±11, DH (kJ mol^-1) = 74±10, DS (J mol^-1 K^-1) = -122±31.