The equimolecular condensation of 2-aminobenzenethiol (1) with 4,8-bis(alkylamino)-1,5-naphthoquinones (2) in ethanol in the presence of HCl gave near-infrared-absorbing 1,5-bis(alkylamino)-4H-benzo[a]phenothiazin-4-ones (3), which existed as predominant tautomers in various solvents. The reaction mechanism was proposed to involve pathways through the O-protonation of 2, followed by the attack of 1 on the resulting ion, the subsequent oxidation, and the acid-catalyzed intramolecular cyclization of the quinonoid intermediate. The tautomeric equilibria of 2, 3, and 5,8-dihydroxy-1,4-naphthoquinone favor the formation of an interconverting hydrogen atom of a higher electron density. The solvatochromic effect of 3 was analyzed by means of the linear solvation energy relationships.
2-aminobenzenethiol (1) 与 4,8- 双(烷基
氨基)-1,5-
萘醌 (2) 在 HCl 存在下于
乙醇中发生等分子缩合,生成了近红外吸收的 1,5- 双(烷基
氨基)-4H-苯并[a]
吩噻嗪-4-酮 (3),在各种溶剂中均以主要同分异构体的形式存在。据推测,反应机理包括 2 的 O-质子化、1 对生成离子的攻击、随后的氧化以及
醌类中间体在酸催化下的分子内环化。2、3 和 5,8-二羟基-
1,4-萘醌的同分异构平衡有利于形成电子密度较高的相互转化氢原子。通过线性溶解能关系分析了 3 的溶解变色效应。