Structure and reactivity in highly halogenated ketazines

The azines of acetophenone and its mono- and di-chlorinated derivatives show a bathochronic shift in the yellow region, but the azine of trichloroacetophenone is colorless. Similar trends are observed in the brominated analogs and in the chlorinated propiophenone azines. The colorless tétrachloropropiophénone azine (13) is shown by X-ray analysis to be nonplanar at the azine atoms (N—N torsion angle, 126.7°). Hexachloroacetophenone azine (9) undergoes displacement of all its chlorines with NaOMe to give the hexamethoxy compound 16, also colorless. With acid, 16 gives the yellow planar (X-ray) ketazine diester 20. These reactions appear to be general for the trichloromethyl group in azines, but not for the α,α-dichloroalkyl group, attempts at the sequence 13 to 28 proving unsuccessful.