Reduction of cyclohexanone 2‐nitrophenylhydrazone. Formation of cyclohexane‐3‐spiro‐3,4‐dihydro‐1,2,4‐benzotriazine

The structure of compound C12H15N3, obtained by Perkin and Riley in 1923, through the reduction of cyclohexanone 2‐nitrophenylhydrazone, was reexamined. This compound, considered originally as 3,4‐cyclotetramethylene‐4,5‐dihydro‐1,2,5‐benzotriazepine (I) and later as 2‐aminophenylazocyclohexene (II), is now defined through the nmr spectrum and chemical behaviour as cyclohexane‐3‐spiro‐3,4‐dihydro‐1,2,4‐benzotriazine (V). It is formed by spontaneous oxidation of the cyclic form of cyclohexanone 2‐aminophenylhydrazone (namely, cyclohexane‐3‐spiro‐1,2,3,4‐tetrahydro‐1,2,4‐benzotriazine) obtained through amino group addition on the hydrazone double bond.