Synthesis of 2, 3-Disubstituted 5, 8-Diamino-1, 4-naphthoquinones

Abstract

In order to see the bathochromic shift due to the amino group in benzenoid ring, 1, 4-naphthoquinone derivatives [7a∼e] having the amino groups at 5, 8-positions and the additional substituents (Cl, Br, CH₃, OCH₃, NH₂) at 2, 3-positions have been synthesized.5, 8-Diamino2, 3-dichloro-[7 a], 5, 8-diamino-2, 3-dibromo-[7 b] and 5, 8-diamino-2, 3-dimethyl-1, 4-naphthoquinones [7 c] were obtained by nitration, hydrolysis and reduction of the corresponding 2, 3disubstituted 5-acetylamino-1, 4-naphthoquinones [7a∼c] (Scheme 1).5, 8-Diamino-2, 3-dimethoxy [7 d] and 2, 3, 5, 8-teramino-1, 4-naphthoquinones[7 e] were synthesized by the reactions of 5-acetylamino-2, 3-dichloro-8-nitro-1, 4-naphthoquinone [5 a] with CH₃Na and potassium phthalimide, respectively (Schemes 2, 3). For these compounds in ethanol, UV and visible absorption spectra were measured. The strongest bathochromic effect was obtained for [7 b]which showed the longest wavelength band at 636 nm. The bathochromic and hypsochromic shifts were observed for the derivatives having electron-withdrawing and electron-donating groups at 2, 3-positions, respectively.