Die Tautomeriegleichgewichte von Dihydrochinoxalinen

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Abstract
The primary product of the two step reduction of 2‐phenylquinoxaline is the 1,4‐dihydrocompound which undergoes a tautomeric rearrangement to the thermodynamically more stable 1,2‐dihydro‐3‐phenylquinoxaline. The 1,4‐dihydro compound is an extremely reactive reducing agent whereas the 1,2‐dihydro form is almost inert against oxidizing agents. Both dihydro forms are in a kinetically hindered equilibrium. The rearrangement requires a transfer of a proton from a nitrogen to a carbon atom and is therefore relatively slow even at pH 0.The 1,2‐dihydro compound cannot take part in redox reactions directly. If this compound is oxidized, the rate determining step is always the reversed tautomeric rearrangement.The effect of the kinetics of the tautomeric rearrangement on the polarographic behavior of the 2‐phenylquinoxaline system is discussed.