Unusual Addition of Hydrogen Chloride to N‐Substituted Quinone Imines.

Addition of hydrogen chloride to quinones and N-substituted quinone imines follows 1,4[1] or 6,3-addition pattern [2], leading to aromatization of the quinoid ring with introduction of chlorine into the aromatic ring. We found that 4-[2-(4-nitrobenzylidene)hydrazono]cyclohexa-2,5-dien-1-one (I) reacts with hydrogen chloride to give 4-[2-(α-chloro-4-nitrobenzylidene)hydrazino]phenol (II). This reaction is unusual, for no chlorine atom is introduced into the aromatic ring, but highly reactive imidoyl chloride II is obtained. 4-[2-(α-Chloro-4-nitrobenzylidene)hydrazino]phenol (II). Concentrated hydrochloric acid, 5 ml, was added to a solution of 1.0 g (4 mmol) of compound I in 100 ml of glacial acetic acid, the mixture was stirred for 45 min, 100 ml of methylene chloride and 150 ml of water were added, the mixture was shaken for 10 min, and the organic phase was separated, washed with a 5% solution of sodium carbonate and water, and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and the brown precipitate was washed with several portions of hexane. Yield 0.81 g (70%), mp 159–162°C. H NMR spectrum, δ, ppm: 10.12 s (1H, NH), 9.11 s (1H, OH), 8.28–8.04 d.d (4H, O2NC6H4, J = 8.9 Hz), 7.24 d (2H, 2-H, 6-H, J = 8.7 Hz), 6.74 d (2H, 3-H, 5-H, J = 8.7 Hz). Found, %: C 53.38; H 4.76; Cl 12.06; N 14.35. C13H10ClN3O3. Calculated, %: C 53.42; H 4.79; Cl 12.12; N 14.38. The H NMR spectra were recorded on a Varian Gemini 2000 spectrometer (400 MHz). The purity of compounds I and II was checked by TLC on Kieselgel 60 F254 plates (Merck) using chloroform–acetone (9 : 1) as eluent.